Wireless Sensor Networks: Applications and Forms

Wireless Sensor Networks: Applications and Forms 1 Wireless Sensor Network In this chapter, wireless sensor network (WSN) principles are being shortly introduced and discussed. In order to increase the level of understanding for analyzing Wireless Sensor Network (WSN) systems it is useful to study the technology behind them the technologies which are presented in this section. Wireless Sensor Networks (WSNs) are distributed and independent sensors that are connected and worked together to measure quantities such as temperature, humidity, pressure, noise levels or vibrations [5]. WSNs can measure vehicular movement (velocity, location, etc.) and monitor conditions such as lightning condition, soil makeup and motion [5]. Nowadays, WSNs are utilized in many common applications such as vehicle applications. Some of vehicle applications are: vehicle tracking and detection, tire pressure monitoring, vehicle speed detection, vehicle direction indicator, traffic control, reversing aid sensors etc. Such applications can be divided in major categories such as safety, security, environment and logistics. To implement WSN in an application and have an efficient system, first we need to consider about WSN technology, components and communication topology and protocols. Therefore, first, in this chapter, basic information about WSN components, the communication devices and process unit of WSN will be described. Then, the chapter will be followed by a description of the WSN topologies and protocols emphasizing on mesh WSN technology with ZigBee Protocol. 1.1 Wireless Sensor Network component To provide comprehensive view of WSN hardware, understanding of WSN components structure is required. Wireless sensors are small microcontrollers equipped with wireless communication device and an energy supplier. The architecture of WSNs is illustrated in Figure 3à ¢Ã¢â€š ¬Ã¢â‚¬Ëœ1 . As Figure 3à ¢Ã¢â€š ¬Ã¢â‚¬Ëœ1 shows the components of WSNs are sensing unit, processing unit, power supplier and communication device. The sensing unit consists of sensors and Analog to Digital Converters (ADCs). ADCs are responsible for gathering the signals and converting them into digital signals data and transfer them through each other using network topology to the processor unit. In the sensing unit, each sensor is called an ‘end node and varies in size and cost. The mission of these multifunction sensor nodes are to sense, process data and collaborate with other nodes [8]. Wireless sensor network can be positioned in two ways, either using a complex technique with the large sensors far from the object or using several sensors with an engineered design on position and topology [5]. In addition, each node provided with a wireless communication transceiver as a communication component. In the process unit, the controller and small memory storage are responsible for managing the collaboration within the sensors to achieve the assigning task. In addition, the communication device with a transceiver makes the network connection. Above all, the essential component of WSN is the power unit, which supports the power for all units [5]. One of the unique characteristics of sensor networks is that they are equipped with an on-board processor. This feature enables them to locally process some simple computations and broadcast only necessary processed data [5]. Network communication is really complicated and needs years of study [8], but to be able to implement WSN, we need to know some basic primary concepts of communication technology such as; network topologies, network protocol and their standards and specifications. 1.2 Communication technology To cover technical aspects of WSN, network topology and network protocol studying is needed. This study will help to provide information about reliability, robustness, security and stability and of WSNs software aspect to answer the research questions RQ. 1 ,RQ. 2 and RQ. 3 . 1.2.1 Topologies in WSN Communication In network communication, the big issue is how data transfers through nodes and nodes interconnect with each other. Several basic network topologies may be used for transmitting to and receiving from a node. The Alliance for Telecommunications Industry Solutions (ATIS) the standards organization of telecommunication industry explained the network topology as â€Å"The physical, real, logical or virtual arrangement of the nods/elements of a network† [9]. The topology shows the diameter and the number of nodes between any two nodes. Moreover how a data process and the data routing complexities are relied on the chosen topology. Consequently, some characteristics of a sensor networks such as latency, robustness and capacity are changed by their topology [10]. Figure 3à ¢Ã¢â€š ¬Ã¢â‚¬Ëœ2 is a graphic mapping of networks topology which shows the links of one or more nodes and explains the physical topology of the network. Despite having the same topology, two networks can differ in transmission rates because of their physical interaction, signal types and distance between nodes [9]. Table 3à ¢Ã¢â€š ¬Ã¢â‚¬Ëœ1 describes the different types of network topology. Table 3à ¢Ã¢â€š ¬Ã¢â‚¬Ëœ1 Topology TYPES [9]. Since Mesh topology is a main topic in the thesis, it is studied more in-depth in this section 1.2.1.1 Mesh Wireless Network Wireless mesh network is a term used when all wireless nodes are connected to each other within an ad-hoc multi-hob and mesh topology. In this network, any pair of nodes is able to communicate between each other within more than one path. In this network each node is used as a router to forward packets to the neighbor nodes which they have linked to. That means all nodes communicate directly or through other midway nodes without any manual configuration. Therefore, this network also called a self-configuration and self-organized network [11; 12]. As described in Table 3à ¢Ã¢â€š ¬Ã¢â‚¬Ëœ1, there are two types of mesh topology ‘Partially connected and ‘Fully connected (See Figure 3à ¢Ã¢â€š ¬Ã¢â‚¬Ëœ3). In a fully connected topology each node has the ability to communicate with all other nodes in the network and creates an interconnection links. By increasing the number of nodes in a mesh network, the number of links increases as well. On the other hand, in a partially connected topology, instead of direct interconnection between nodes, each node has two or more links to others to provide alternate routing and traffic balancing. Due to more links and indirect connections between nodes, traffic can flow through one or more router nodes to the destination [7] and create more reliable interconnections between nodes. Moreover, in partial network, the nodes are connected to either the node with higher rate of data transaction or the nearest neighbor node while in fully connected network all nodes have a direct links with each other. This multiple link path conducts a reliable communication. Therefore, whenever a connection fails or a node breaks down, the packages can automatically change their path by ‘jumping from a disconnected node. This is often called the self-healing of the network. This means that the networks connection stability and reliability are not essentially affected by node failures [11]. Due to the characteristics of wireless sensor network mesh, this network is self-configuring and self-organizing network in which each end-node is also used as a router (dual role- data originator /data router) to forward the signal packages all the way back of the main gateway. Therefore, due to the characteristics of mesh networks, this network is becoming one of the most implemented networks which able to have the flexible architecture for the network, easy self-configuration and robust fault tolerance connectivity [11; 12]. Additionally, the self-configuring characteristic of mesh WSN, bring the ability for the network to connect or disconnect nodes from the network. This brings the ability to grow/decrease the network by adding/removing nodes of a system. Mesh WSN has reliable self-healing and robust fault tolerance. This means if ­Ã‚ ­Ã‚ ­Ã‚ ­Ã‚ ­Ã‚ ­ a node fails or breaks down the signal packages jump from the disconnected node and automatically conducts a new path through the nearest node. However, the new path imposes re-routing and re-organizing to the network [5], which consumes too much power from the system. Therefore, having a power-aware protocol and algorithm is necessary for mesh network. ZigBee protocol is one of the protocols which provides this ability for WSN. 1.2.2 Protocols in WSN Communication WSN systems include variety of protocols for communication. Protocols need to program in different architectural layers. One of these architectural standard is OSI (Open System Interconnection) framework. In this session a brief introduction of each protocol and OSI are delineated. Figure 3à ¢Ã¢â€š ¬Ã¢â‚¬Ëœ4 shows the graphic overview of all wireless network technologies. This figure illustrated IEEE PAN/LAN/MAN technologies and clearly shows how these standards and protocols can be used in different conditions. For instance, 3G protocol is used to cover a long range of audio information in a wide area network (WAN) while for the same information in a short range and personal area network (PAN), Bluetooth is better. The standard conceptual rules set for data representation, data communication and error detection across two ends in telecommunication, are called communication protocols. These abstract rules represent in different layers of communication. There are different protocol stacks introducing different architectures for these layers such as AppleTalk, Distributed Systems Architecture (DSA), Internet protocol suite (TCP/IP) and Open Systems Interconnect (ISO/OSI). Figure 3à ¢Ã¢â€š ¬Ã¢â‚¬Ëœ5 (a) illustrates the different layers of an OSI Model and their functionalities. The OSI model has seven layers and each layer provides services for the upper layer and requests services from the lower layer. Figure 3à ¢Ã¢â€š ¬Ã¢â‚¬Ëœ5 (b) shows the typical communication protocols layers. Each of these layers has to deal with different issues regarding the communication procedure. As the typical protocol stack model shows in Figure 3à ¢Ã¢â€š ¬Ã¢â‚¬Ëœ5 the communication protocols should implement all layers from bottom to top. In addition, a management protocol needs to be applied in each layer to manage power efficiency, robust connectivity and connection reliability (see: Figure 3à ¢Ã¢â€š ¬Ã¢â‚¬Ëœ5 b). Below, rules and functionality for each layer are described: * Physical layer: is responsible for signal processing and physical interface connectivity between a device and physical medium and used bit stream in its data unit. It acted as communication channel for sensing and actuation in cost-efficient and reliable manner. Some examples of this layer are: IEEE 802.11b/g Wi-Fi, IEEE 802.15.1 Bluetooth, IEEE 802.15.4 ZigBee, etc. [7] * Data link layer: provides functionality toward channel sharing, Medium Access Control (MAC-Layer), timing (e.g. data time arrival), local link and capacity. It is responsible for detecting and correcting the data errors in physical layer and control the locality data comparison. It follows the protocols such as point-to-point protocol (PPP) and IEEE 802 Local Link Control (LLC). [7] * Network layer: is responsible for network routing functionality, network security, energy and power efficiency and reliability of the communication. It includes the network topology management and manages the information and detects errors in data transfer from router to router. A number of protocols is address in this layer such as: Internet protocol (IP), Threshold Sensitive Energy Efficient Sensor Network Protocol and etc. [7]. * Transport layer: provides end-to-end transportation (distributing and gathering) of data between end users. It includes storage and responds for caching and controlling the data to recover them back to the initial message that has been sent. Best-known protocols for this layer are Transmission Control Protocol (TCP) and User Datagram Protocol (UDP) [7]. * Upper layers: The Upper Layers are responsible for application processing, external query processing and etc. Upper layers include presentation layer session layer and application layer [7]. The summary of these standards and protocols are shown in Figure 3à ¢Ã¢â€š ¬Ã¢â‚¬Ëœ6 Among all the standard and protocols, IEEE PAN/LAN/MAN technologies are the ones applied in the majority of commercialWSNs to support physical layer and link-data layer signal transmission. As SOHRABY and ZNATI (2007) mentioned, the most common best-known protocols are:† (1) the IEEE 802.15.1 (also known as Bluetooth); (2) the IEEE 802.11a/b/g/n series of wireless LANs; (3) the IEEE 802.15.4 (ZigBee); (4) the MAN-scope IEEE 802.16 (also known as WiMax); and (5) radio-frequency identification (RFID) tagging† [7]. Each of these protocols has their own benefits and constraints. The comparisons between IEEE technologies are mentioned in Table 3à ¢Ã¢â€š ¬Ã¢â‚¬Ëœ2. As Table 3à ¢Ã¢â€š ¬Ã¢â‚¬Ëœ2 shows the IEEE 802.15.4 standard provides data rate of 20 to 250 kbps and operates in the 2.4-GHz ISM band. This standard covers signals in range of 10 m and requires the lowest power among other IEEE class. While IEEE 802.11a/b/g/n transmits the data in the rate of 54 Mbps ideal for wi reless internet connections and operates in the 2.4-GHz ISM (Industrial, Scientific and Medical) radio band as well as the 5-GHz ISM / 5-GHz U-NII (Unlicensed National Information Infrastructure) radio band. However, it requires much higher power consumption than IEEE 802.15 [7]. Recently, researchers put much effort to develop â€Å"a cost-effective standards-based wireless networking solution that supports low-to medium data rates, has low power consumption, and guarantees security and reliability† [7]. ZigBee Alliance is an association of companies which aims to provide such a standard for WSN consumers. Their mission is to have a simple, reliable, low-cost, low-power and standards-based wireless platform 1.2.2.1 ZigBee standard The ZigBee standard builds on IEEE 802.15.4 and is suitable for remote monitoring and controlling applications. Although it has lower-data-rates than the other standards, its reliability, security, long life battery with less complexity mechanism make it ideal for building automation in industrial network applications. The architecture of the ZigBee stack is established on the Open System Interconnection (OSI) model. The IEEE 802.15.4 defines the physical layer (PHY) and medium access control (MAC) sub-layer and In addition, ZigBee Alliance defines other functionalities for upper layers [7]. Figure 3à ¢Ã¢â€š ¬Ã¢â‚¬Ëœ7 is a graphic overview of ZigBee protocol stack and shows the responsibility areas of IEEE 802.15.4, ZigBee Alliance platform and users applications [7]. This picture also shows the basic functionality of each layer. The data transmission service is provided by PHY layer and the protocol in this layer enables the connection between data units and the physical radio channel. ZigBee provides three different frequency band options for PHY layer. First, the transmission data-rate of 250kbps in 16 channels at 2.45GHz (Global) frequency. Second, with 40Kbps in 10 channels at 915MHz (Americas). And the last one, with 20kbps in 1 channel at 868MHz (Europe). The higher data-rate causes a higher order in modulation design and the lower frequency cause a larger cover area and better sensitivity. Depending on the power output, the transmission distance rate can change from 1 to 100 meters. (For more detail information see: Table 7à ¢Ã¢â€š ¬Ã¢â‚¬Ëœ1 in Appendix A) ZigBee WSN has the ability to have static or dynamic network/component with either star or mesh topology and it has three types of nodes: a ZigBee Coordinator (ZC), ZigBee Routers (ZR), and ZigBee End-Devices (ZED). In order to have a communication protocol and physical connection both PHY layer and MAC sub-layers of the architecture should be defined upon agreement between server and clients. These layers require manual administrative procedures setting for server/client gateway. The next three levels namely: the network layer, security protocol and transport layer are defined by ZigBee alliance platform automatically. The last layer, application layer, has to interact with the user-interface and other applications; it ought to be programmed with high-level language so that integration with any existing devices applications becomes more conveniently practical. The ZigBee stack in gateway is responsible for all the network functionality such as network process management, authentication of the joined nodes, binding nodes and routing the messages throughout the network. ZigBee stack as a standard protocol, has clusters and libraries for improving the implementation process, therefore, using ZigBee compare to other protocols makes the system (including both hardware and software) development process much faster and easier. On the other hand, such standardisation provides easiness of adopt with third party sensors regardless of manufacturer, which might be attached to the network later. 2 Software Aspects To address the research question regarding the reliability, robustness, and security of any WSN application, it is essential to investigate the software architecture of that network. For convenience in description of the architecture of a WSN application, it is divided into three segments: Physical devices (such as lamps, sensors, nodes), Communication Protocol (terminals and servers, bridge, switch, network topology and standard) and Carried Information (application, functions, etc.). Any attempts to retain a precise design on software architecture for each part will cause an effective data transmission, which ensures reliability and security of the system [7]. Hence achieving any desired data transmission precision level in a WSN, network management (NM) techniques are applicable. Such techniques assist in network status monitoring, reliability and security amendment, and cooperation supervision between components [7]. NM techniques could also detect and resolve network faults in addition to restoring the system respectively [7]. In practice, designing WSN application necessitates tailoring NM techniques for each architectural segment. Various NM techniques regarding each segment are summarized as follows [7; 12; 5]: a) Physical architecture: Sensing and processing management, operation and administration, fault tolerance, maintenance, energy efficiency management, configuration management, performance management, security management, network element management. b) Communication architecture: Network management, networking protocols, network topology, function management, monitoring functions, fault management, performance management, security management, service management and communication, maintenance management, network configuration and organization, network behavior, data delivery model, sensor mobility, naming and localization, sensing coverage area, communication coverage area energy efficiency management c) Information architecture: Real-time information management, mapping management, service management, analyze information, control application, business application management report management, sending and receiving commands or response, naming, localization, maintenance, fault tolerance Aforementioned NM techniques enhance quality of the system. According to ISO 9126-1 software quality model Table 4à ¢Ã¢â€š ¬Ã¢â‚¬Ëœ1 [13; 14; 15], the quality characteristics of a system could be divided into six fundamental properties: functionality, reliability, usability, efficiency, maintainability, and portability. According to the same documentation, these characteristics are broken to sub-characteristics such as suitability, security, maturity, fault tolerance, adaptability, analyzability, stability, testability and so on [13]. However, focusing on all subcategories collectively exceeds the time horizon of this research, from this stance three dimensions namely reliability, robustness and security are brought into attention. This section will be divided to two subsections describing the architecture issues and NM techniques for (1) Reliability and Robustness, (2) Security, of WSN and other characteristics is relegated to future studies. 2.1 Reliability and Robustness In WSNs context, the probability that a network functions properly and aggregates trustworthy data without any interruption continuously, is usually referred to as reliability characteristic of the network [23; 20]. According to ISO 9126-1 software quality documentation, reliability characteristic shows the capability of a network to maintain or re-built (re-start) the service in certain period of time [13]. So, it is important that during long sensing, the network has to service up continuously. Reliable service of a network includes precise and proper sensing, delivering and sending acceptable data to the base station. In other words as Taherkordi et al. (2006) put: â€Å"The less loss of interested data, leads us to higher reliability of a system†. Systematic approach perceives reliability as probability of data delivery to the base station rather than point-to-point reliability [16]. Robustness defined by Sohraby et al. (2007) as: â€Å"a combination of reliability, availability, and dependability requirements†, reflects the degree of the protocol insensitivity to errors and misinformation†. Achieving system robustness in WSN, necessitates system capability to detect, tolerate and confine errors as well as reconfigure and restart the network respectively [7]. According to the given definition by Sohraby et al. (2007), it is apprehensible that reliability and robustness share commonalities with each other; this is the main rational behind discussing these two attributes together in this section [7]. Considering the nature of communication in WSN, a network is unpredictable and prone to fail caused by any physical damages in hardware devices, energy depletion, communication link error, information collapses in packages and etc. [17; 16]. Therefore, one of the critical issues in design phase of WSN is applying fault tolerance techniques to optimize the network so that reliability and robustness attained [17]. These techniques enable the network to withstand and recover any upcoming failure and restart operation [13]. Liu et al. (2009) categorized fault tolerance techniques into: node placement, topology control, target and event detection, data gathering and aggregation, and sensor surveillance. Reminding from the beginning of this chapter architecture design divided into three segments. Table 4à ¢Ã¢â€š ¬Ã¢â‚¬Ëœ2 depicted a summary of the plausible related faults and their solutions in each segment. In the following, each aforementioned fault tolerance techniques are being discussed in each design segment. Table 4à ¢Ã¢â€š ¬Ã¢â‚¬Ëœ2 The most probable fault and their fault tolerance solutions in WSN [17; 7; 18] 2.1.1 Reliability and Robustness of Physical Architecture: Fault: any physical interruption in sensor surveillance Solution: Node placement management and signal-effect management First item that should be considered in designing physical components architecture for reliability and Robustness is: physical placement and signal-effect management. As it is mentioned in section 3, although the mesh network communication is self-organize topology and does not need any manual configuration to bind the network for mobile sensors, the physical architecture and the location schema of the hardware components, sensors and gateways need to be designed carefully [7]. As a characteristic of mesh WSN, the sensors in network are free of any installation restrictions, even though, the placement should be far from any physical destruction or hostile locations. Inappropriate physical placement of sensor transmitters and gateway antenna can cause noise or significant lost in signals [7]. In addition, the signal coverage is decayed by surrounding objects and materials such as metal wall and the like. (E.g. exterior wooden, concrete, brick or gypsum frame, block or wall). Especially in the case of vehicles, the main body can impose such problem and henceforth installation of the sensors in this manner would be delicate. Moreover, the signal waves might be faded and affected during the transmission, due to various physical phenomena such as reflection, diffraction or scattering [7]. These effects would cause significant interruption in sensor surveillance. Therefore, it is important to manage these signal-effects in early stage of WSN physical architecture design. Reflection occurs when electromagnetic wave of signals is duplicated due to impinge of the wave on large object or surface such as walls, buildings and the Earth [7]. Therefore, all the reflection of the walls and also the Earth should be acknowledged in physical architecture design. Diffraction refers to any defection and obstruction in waves caused by irregular sharp edges during the data transmission between the transmitter and receiver [7]. In this case, designers have to be prudent in sensors placements in the proximity of sharp edges and corner angels. Scattering refers to any deviation from straight line. Environmental obstacles in the propagation path affect passing waves from their original structure. Even small irregular object such as street signs, and lampposts might encounter and scatter the wave. Hence WSN should be design to face with any irregular scattering during the wave transmission. Above all, the mobility of sensors and surrounding objects might fade the signals and add noises that should be considered in architecture design [7]. These issues are the basic physical factors, which cause major fault in data aggregation of WSN and cut down reliability and robustness. These destructive signals need to be subtracted from the received signal paths [7] before sending the data to gateway. Therefore, reflection, diffraction and scattering should be considered not only by designers in the physical components placements, but also by programmers in network development. Fault: Sensors failure Solution: Hardware replacement The next issue that needs to be considered in designing the physical architecture of a WSN is hardware failure. Sensors energy suppliers or any damages to the sensors and/or their transmitters are the sources of hardware failure. Regardless of source of failure, the WSN must be capable of functioning as well as replacing and switching sensors when necessary. Additionally, any changes in the physical components, on one hand, needs an explicit and well-defied consideration on security issue to prevent any potential threats, and on the other hand, needs an adaptable and configurable communication connection network [18]. 2.1.2 Reliability and Robustness of Communication Architecture Fault: communication link errors Solution:Topology control and event detection , Replicated services in communication model, Communication link error is an important concern in dealing with reliability and robustness of a network in communication architecture. The sensors in WSN are prone to fail and make link errors in point-to-point reliability of communication protocol. Therefore, it is the network topology responsibility to detect the errors and guarantee the overall reliability of the syste

Factors Affecting Solubility

There are three main factors that control solubility of a solute. (1) Temperature (2) Nature of solute or solvent (3) Pressure EFFECT OF TEMPERATURE Generally in many cases solubility increases with the rise in temperature and decreases with the fall of temperature but it is not necessary in all cases. However we must follow two behaviours: In endothermic process, solubility increases with the increase in temperature and vice versa. For example: solubility of potassium nitrate increases with the increase in temperature. In exothermic process, solubility decrease with the increase in temperature.For example: solubility of calcium oxide decreases with the increase in temperature. Gases are more soluble in cold solvent than in hot solvent. NATURE OF SOLUTE AND SOLVENT Solubility of a solute in a solvent purely depends on the nature of both solute and solvent. A polar solute dissolved in polar solvent. Solubility of a non-polar solute in a solvent is large. A polar solute has low solubil ity or insoluble in a non-polar solvent. EFFECT OF PRESSURE The effect of pressure is observed only in the case of gases. An increase in pressure increases of solubility of a gas in a liquid.For example carbon dioxide is filled in cold drink bottles (such as coca cola, Pepsi 7up etc. ) under pressure. Properties of Solution Concentration The concentration of a solution is the measure of how much solute and solvent there is. A solution is concentrated if it contains a large amount of solute, or dilute if contains a small amount. Molarity Molarity is the number of moles of solute per litre of solution. It is abbreviated with the symbol M, and is sometimes used as a unit of measurement, e. g. a 0. 3 molar solution of HCl. In that example, there would be 3 moles of HCl for every 10 litres of water (or whatever the solvent as). Molality Molality is the number of moles of solute per kilogram of solvent. It is abbreviated with the symbol m (lowercase), and is sometimes used as a unit of me asurement, e. g. a 0. 3 molal solution of HBr. In that example, there would be 3 moles of HBr for every 10 kilograms of water (or whatever the solvent was). Mole Fraction The mole fraction is simply the moles of solute per moles of solution. As an example, you dissolve one mole of NaCl into three moles of water. Remember that the NaCl will dissociate into its ions, so there are now five moles of particles: one mole Na+, one mole Cl-, and three moles water.The mole fraction of sodium is 0. 2, the mole fraction of chloride is 0. 2, and the mole fraction of water is 0. 6. The mole fraction is symbolized with the Greek letter (chi), which is often written simply as an X. Dilution Dilution is adding solvent to a solution to obtain a less concentrated solution. Perhaps you have used dilution when running a lemonade stand. To cut costs, you could take a half-full jug of rich, concentrated lemonade and fill it up with water. The resulting solution would have the same total amount of sugar a nd lemon juice, but double the total volume. Its flavour would be weaker due to the added water.The key concept is that the amount of solute is constant before and after the dilution process. The concentration is decreased (and volume increased) only by adding solvent. Thus, the number of moles of solute before and after dilution are equal. moles1 = moles2 By definition of molarity, you can find the moles of solvent. M x V = moles Substituting the second equation into the first gives the dilution equation. M1 x V1 = M2 x V2 To determine the amount of solvent (usually water) that must be added, you must know the initial volume and concentration, and the desired concentration.Solving for V2 in the above equation will give you the total volume of the diluted solution. Subtracting the initial volume from the total volume will determine the amount of pure solvent that must be added. Ionic Solutes When ionic compounds dissolve in water, they separate into ions. This process is called diss ociation. Note that because of dissociation, there are more moles of particles in the solution containing ions than there would be with the solute and solvent separated. If you have two glasses of water, and you dissolve salt into one and sugar into the other, there will be a big difference in concentration.The salt will dissociate into its ions, but sugar (a molecule) will not dissociate. If the salt were NaCl, the concentration would be double that of the sugar. If the salt were MgCl2, the concentration would be triple (there are three ions). Solubility Rules Not all ionic compounds are soluble. Some ionic compounds have so much attractive force between their anions and cations that they will not dissociate. These substances are insoluble and will not dissolve. Instead, they clump together as a solid in the bottom of solution. Many ionic compounds, however, will dissociate in water and dissolve.In these cases, the attractive force between ion and water is greater than that between cation and anion. There are several rules to help you determine which compounds will dissolve and which will not. Solubility Rules 1. All compounds with Group 1 ions or ammonium ions are soluble. 2. Nitrates, acetates, and chlorates are soluble. 3. Compounds containing a halogen are soluble, except those with fluorine, silver, or mercury. If they have lead, they are soluble only in hot water. 4. Sulfates are soluble, except when combined with silver, lead, calcium, barium, or strontium. . Carbonates, sulfides, oxides, silicates, and phosphates are insoluble, except for rule #1. 6. Hydroxides are insoluble except when combined with calcium, barium, strontium, or rule #1. Sometimes, when two different ionic compounds are dissolved, they react, forming a precipitate that is insoluble. Predicting these reactions requires knowledge of the activity series and solubility rules. These reactions can be written with all ions, or without the spectator ions (the ion that don't react, present o n both sides of the reaction), a format known as the net ionic equation.For example, silver nitrate is soluble, but silver chloride is not soluble (see the above rules). Mixing silver nitrate into sodium chloride would cause a cloudy white precipitate to form. This happens because of a double replacement reaction. Electrolytes When solutes dissociate (or if a molecule ionizes), the solution can conduct electricity. Compounds that readily form ions, thus being good conductors, are known as strong electrolytes. If only a small amount of ions are formed, electricity is poorly conducted, meaning the compound is a weak electrolyte.A strong electrolyte will dissolve completely. All ions dissociate. A weak electrolyte, on the other hand, will partially dissociate, but some ions will remain bonded together. Colligative Properties Some properties are the same for all solute particles regardless of what kind. These are known as the colligative properties. These properties apply to ideal solut ions, so in reality, the properties may not be exactly as calculated. In an ideal solution, there are no forces acting between the solute particles, which is generally not the case. Vapor PressureAll liquids have a tendency for their surface molecules to escape and evaporate, even if the liquid is not at its boiling point. This is because the average energy of the molecules is too small for evaporation, but some molecules could gain above average energy and escape. Vapor pressure is the measure of the pressure of the evaporated vapor, and it depends on the temperature of the solution and the quantities of solute. More solute will decrease vapor pressure. The vapor pressure is given by Rauolt's Law, where X is the mole fraction of the solvent.Notice that the vapor pressure equals that of the pure solvent when there is no solute (X = 1). If X = 0, there would be no vapor pressure at all. This could only happen if there were no solvent, only solute. A solid solute has no vapor pressure . P solution = P pure solvent (X solvent) If two volatile substances (both have vapor pressures) are in solution, Rauolt's Law is still used. In this case, Rauolt's Law is essentially a linear combination of the vapor pressures of the substances. Two liquids in solution both have vapor pressures, so this equation must be used. P solution = P1 (X1) + P2(X2)The second equation shows the relationship between the solvents. If two liquids were mixed exactly half-and-half, the vapor pressure of the resulting solution would be exactly halfway between the vapor pressures of the two solvents. Another relation in Henry's Law, which shows the relationship between gas and pressure. It is given by Cg = k Pg , where C is concentration and P is pressure. As the pressure goes up, the concentration of gas in solution must also increase. This is why soda cans release gas when they are opened – The decrease in pressure results in a decrease in concentration of CO2 in the soda.Boiling Point Elev ation A liquid reaches its boiling point when its vapor pressure is equal to the atmosphere around it. Because the presence of solute lowers the vapor pressure, the boiling point is raised. The boiling point increase is given by: ?T solution = Kb X m solution The reduced vapor pressure increases the boiling point of the liquid only if the solute itself is non-volatile, meaning it doesn't have a tendency to evaporate. For every mole of non-volatile solute per kilogram of solvent, the boiling point increases by a constant amount, known as the molal boiling-point constant (Kb).Because this is a colligative property, K2 is not affected by the kind of solute. Freezing Point Depression A liquid reaches its freezing temperature when its vapor pressure is equal to that of its solid form. Because the presence of the solute lowers the vapor pressure, the freezing point is lowered. The freezing point depression is given by: ? T solution = K f X m solute Again, this equation works only for non- volatile solutes. The temperature of the freezing point decreases by a constant amount for every one mole of solute added per kilogram solvent. This constant (K f) is known as the molar freezing-point constant.Osmosis If you studied biology, you would know that osmosis is the movement of water through a membrane. If two solutions of different molarity are placed on opposite sides of a semipermiable membrane, then water will travel through the membrane to the side with higher molarity. This happens because the water molecules are â€Å"attached† to the solvent molecules, so they cannot travel through the membrane. As a result, the water on the side with lower molarity can more easily travel through the membrane than the water on the other side. The pressure of this osmosis is given in the equation. ? = MRTWhere pi is the pressure, M is molarity, R is the gas constant, and T is temperature in Kelvin. Electrolytes and Colligative Properties When one mole of table salt is added t o water, the colligative effects are double those that would have occurred if sugar were added instead. This is because the salt dissociates, forming twice as many particles as sugar would. This dissociation, called the Van't Hoff Factor describes how many particles that are dissociated into the solution and must be multiplied into the Boiling Point Elevation or Vapor Pressure Lowering equations. Different ways of expressing the concentration of solutionsMass Percentage The mass percentage of a component in a given solution is the mass of the component per 100g of the solution. For e. g. , if WA is the mass of the component A, WB is the mass of the component B in a solution. Then, Example: A 10% solution of sodium chloride in water (by mass) means that 10g of sodium chloride are present in 100g of the solution. Volume percentage This unit is used in case of a liquid dissolved in another liquid. The volume percentage is defined as the volume of the solute per 100 parts by volume of s olution. For e. g. , If VA is the volume of component A present is Vsol volume of the solution.Then, For e. g. , a 10% solution of ethanol C2H5OH, in water (by volume) means that 10cm3 of ethanol is present in 100cm3 of the solution. Strength of a solution is defined as the amount of the solute in gms, present in one litre of the solution. It is expressed as gL-1. Mathematically, Molarity Molarity of a solution is defined as the number of moles of solute dissolved per litre of solution. Mathematically, For e. g. , If ‘a' is the weight of the solute (in gms) present in VCC volume of the solution. Then, Molarity is expressed by the symbol M. It can also be expressed as, NormalityNormality of a solution is defined as the number of gram equivalents (gm. e) of a solute dissolved per litre of the given solution. Mathematically it is, For e. g. , If a is the weight of the solute (in gms) present in VCC volume of the solution. Then, Normality is expressed by the symbol N. It can also be expressed as, Relationship between molarity and normality The molarity and normality of a solution is related to each other as follows: Molality Molality of a solution is defined as the number of moles of solute dissolved in 1000g of a solvent. Mathematically, it is expressed as Molality is expressed by the symbol m.Molality does not change with temperature. Formality In case of ionic compounds like KCl, CaCO3 etc. Formality is used in place of molarity. It is the number of gram formula masses of solute dissolved per liter of the solution. It is denoted by the symbol F. Mathematically it is given as, Mole Fraction It is the ratio of number of moles of one component (solute or solvent) to the total number of moles of all the components (solute and solvent) present in the solution. It is denoted by the symbol X. Let us suppose that a solution contains two components A and B and suppose that nA moles of A and nB moles of B are present in the solution then,Adding eq (i) and (ii) we g et XA + XB = 1 Parts per million (ppm) When a solute is present in very small amounts, its concentration is expressed in parts per million. It is defined as the amount of the solute present in one million parts of the solution. It may be noted that the concentration units like molarity, mole fraction etc. are preferred as they involve the weight of the solute and solvent, which is independent of the temperature. But units like, molarity, normality etc. , involve volume of the solution, hence changes with temperature.

Ideas, Formulas and Shortcuts for Persuasive Essay Topics 2016

Ideas, Formulas and Shortcuts for Persuasive Essay Topics 2016 The Upside to Persuasive Essay Topics 2016 Persuasive essays are an excellent approach to encourage the reader to check at a particular topic in a different light. Exactly like an argumentative essay, a persuasive paper demands an adequate degree of expertise and knowledge of a particular field. In general, you can observe that writing a persuasive essay isn't a brain surgery. Always remember an ideal persuasive essay needs to be persuasive. Naturally, giving a wonderful persuasive speech requires more than simply selecting a fantastic topic. You should make sure you've picked among the best ideas for persuasive speech and that you've used the proper words to demonstrate your opinion. Then it gets even more difficult to find out your speech topic. For instance, a terrific speech topic may not be in a position to hold an audience's attention if it's not structured and organized properly. The direction you deliver your speech facing the audience will also play an extremely major role on how funny it's going to be and how it is able to impact your audience. To begin with, if you're arranging a persuasive speech, you ought to think about a topic that may create mental pictures in the minds of your audience. By understanding your audience it will be simpler that you explain yourself, and it'll be simpler for your audience to understand you. What's more, the audience was served and they win. There are lots of interesting persuasive speech topics that you are able to use in your next academic assignment, but you ought to make sure your essay is pertinent to the subject you're studying. You should utilize APA reference tools to aid in writing your essay the right way or seek the services of an expert essay writer that may write the essay working with the APA reference tools. Before students begin to write, it is a fantastic idea for them to earn a list of the points they would like to make to their readers. A student ought to keep in contact with the hottest trends and know which persuasive essay topics are related to sound convincing in regards to defending personal opinions. As a way to prevent that from happening, here are a few pointers about how to opt for the very best persuasive speech topics. Our topics are good since they won't leave listeners indifferent. If you're unable to think of an intriguing topic, your readers may not be tempted to listen to you till the very end. When choosing persuasive speech topics, you also need to think about where you're comfortable. Get the Scoop on Persuasive Essay Topics 2016 Before You're Too Late A few of the topics also fall into other categories and we've posed the topics as questions so that they are easily adapted into statements to fit your own viewpoint. Well, first, you are going to want to find good persuasive speech topics. Take notes concerning all prospective topics you'll be able to consider. There are several persuasive essay topics to pick from to finish your high school or college assignment. Once you're able to narrow your audience, reflect in their views you are now able to select your topic. Define the key points that you wish to get across and set them in a persuasive topic. For instance, if you're writing about the subject about elite athletes, you could argue that Michael Jordan is an elite athlete due to the skills which he has. Choosing Persuasive Speech Topics A persuasive speech can't be effective in the event the speaker chooses the incorrect topic. Textbooks ought to be free. Students ought to be permitted to pray in school. Language should not be permitted to change.

How To Kill a Mockingbird showed Americans new perspectives on racism, sexism, and the Great Depression - Free Essay Example

Sample details Pages: 3 Words: 871 Downloads: 1 Date added: 2019/02/20 Category Literature Essay Level High school Topics: To Kill a Mockingbird Essay Did you like this example? To Kill A Mockingbird by Harper Lee seemed like the perfect book for this analysis because it is a classic and it is full of symbolism. The setting of the book is about the town Maycomb, Alabama in the 1930’s from the perspective of an eight year old tom-boy like girl, Scout Finch. This paper discusses how the novel portrays the time period and how it showed Americans new perspectives on issues like racism, sexism, and the Great Depression. In the 1930’s African Americans were still very segregated from the rest of the population and treated differently. This is one of the main issues that is covered in the book through the trial of an African American man Tom Robinson. Mayella Ewell is a young girl that accuses Tom of hitting and later raping her. When Tom goes on trial he is given a public defender which is Scout and Jem’s father, Atticus Finch. Because of the society that they live in Atticus knows that there is no hope for Tom, even though he will try his absolute best to convince the judge and jury of his innocence. When Tom does go to jail there is no surprise there because of all the racism of the time period his trial never stood a chance. The racist South had so many regulations and rules in place to limit the rights of any and all African Americans, like Jim Crow laws and the â€Å"separate but equal† case. The civil war led to the freedom of all African American slaves and indentur ed servants, but that was federal law. Soon after the war Southern states and local governments found a loophole and started enforcing Jim Crow laws, meant to limit the rights of African Americans. These laws entirely segregated the population once again by giving African American people separate drinking fountains, schools, parks, public transportation, and the list goes on; these laws did not end until 1965 when Lyndon B. Johnson signed the civil rights act. Another one of the biggest sectors revolving around racism at the time was the idea that â€Å"separate but equal† was a justifiable and fair practice that could be applied to society. This doctrine was obviously false and unsuccessful, just like the Jim Crow laws, it separated the nation even more and only caused more tension. These two laws were few of many, but they all led to lives, similar to the fictional one of Tom, being destroyed for unjustifiable reasons. Don’t waste time! Our writers will create an original "How To Kill a Mockingbird showed Americans new perspectives on racism, sexism, and the Great Depression" essay for you Create order The next big issue that Lee tackles in her novel was the high level of sexism in the south during the 1930’s. Sexism was an issue everywhere in the nation at the time, but it was definitely more prominent in the South. An example in the book would be how Scout loves to be a tom-boy and play outside and participate in sports, but then when she has to go to church or be presented in front of the town Calpurnia makes her wear proper girls clothing. Even when she is playing with Dill and Jem the boys will say mean things about her gender, or they’ll leave her behind to go do something else, for example skinnydip in the lake(pg 125). Even the women in her community judge her for how she acts, walks, and talks(pg 126). It is very evident that in the South women are held to a certain standard and they are supposed to fulfill the role of being dainty and dependent on the man for their sole source of survival. The time period of this book lines up directly with the time of the Great Depression. This may not show within the Finch household because they are so well off, but it certainly shows throughout the rest of the town. The small town is described as â€Å"sagging† and â€Å"the streets turning into red slop† whenever it rained, describing this rundown town as if it were falling apart(pg 67). The imagery gives the reader a feel for what the Great Depression did to the South, it essentially destroyed it. People and buildings of the town seem like they’re all falling apart and with a gust of wind they just might collapse, because people could barely afford the basic necessities during this time. Many families had one or two sources of income and they were probably left unemployed at this time. With a lack of money they had to find cheaper alternatives to entertainment, people turned to radios, stamps and card collections, or sports. In the novel Scout and Jem wo uld play with anything that they could find outside, this may not have been a necessity for them, but they probably did not have that many toys considering the circumstances(pg 170). Also the â€Å"gifts† left by Boo Radley were often very simple pleasures like pocket change or strips of gum, because things like that were often considered luxuries(pg 126). This novel was an excellent choice and opened up so many issues with history. It brought to the table issues about sexism, racism, and what people went through in the Great Depression. Making the protagonist an eight year old girl opened up the perspectives and allowed readers to see a new side of the story.