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41 Cards in this Set
- Front
- Back
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What is thermal pollution: |
Some industries, especially coal-burning or nuclear power stations produce large amounts of waste heat. In some places, these plants(power stations) are situated beside lakes or the sea so that the water can be used for cooling the equipment. Typically, lake water is pumped through the equipment, then hot water discharged back into the lake. This is thermal pollution, and is very destructive to aquatic habitats |
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Why is thermal pollution so destructive to aquatic habitats |
The main problem is a matter of solubility Oxygen, and other gases, are sparingly soluble in water. Aquatic organisms are totally dependant on this low concentration of dissolved gases for their survival. The problem is, that the solubility of gases decrease as the temperature rises. If the water temperature rises by as little as 5 degrees, the dissolved oxygen concentration drops by 20% and fish begin to suffocate. Not only that, but increases temperature can interfere with the normal breeding cycles and alter the delicate balance between populations of food plants, disease, microbes, parasites, etc. Habitat destroyed! |
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What is calorimetry
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Is a technique used to measure the energy change occurring during chemical processes. The word is device from the 'calorie'. The equipment used to make energy measurements is called a 'calorimeter'
Since many chemical processes occur in water, and because water has such a high Specific Heat Capacity (i.e. it can absorb lots of energy with little temperature change) calorimetry often uses water as the 'working fluid' or medium used ot absorb the heat energy |
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Specific heat capacity |
Is a measrue of how much heat energy (in joules) is required to change the temperature of 1 gram of substance, by 1 degree celsius. The units of Heat Capcity, therefore, joules per degree per gram (J/degree/gram) |
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What is an endothermic reaction? draw diagram |
(Endo=to go in) are the reactions that absorb energy...those where you must supply energy to make it happen |
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What is an exothermic reaction? draw diagram |
(Exo=to go out) are the reactions that produce and release energy The amount of energy involved in the 'delt-H' for the process, and is measured per mole of the substance(s) involved. When the chemicals lose energy, the temperature in the calorimeter rises, becuase the erngy release heats up the water in the calorimeter. This is why, when the temperature rises, the energy quantity is considered negative... the chemicals involved have LOST this amount of heat energy |
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Heat of solution: |
Is the common name for the energy change that occurs when 1 mole of a solute dissolves in water 'delta Hsol' is negative if energy is released (exothermic: the calorimeter temperature rises) examples: soluable hydroxides (e.g. NaOH, KOH) 'delata H' is postive if energy is absorbed (endothermic: the calorimeter temperature falls) examples: ammonium nitrate(NH4NO3), ammonium chloride(NH4CI) |
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Limitations of calorimetry |
- assumed calorimeter iteself does not absorb a singifcant amount of heat energy error minised by using copper reaction vessel, since the very low Specific Heat Capacity of copper means it absorbs little energy - no heat lost or gained between the calorimeter and the surroundings error minimised by good heat insulation of the calorimeter - Specific heat capacity of solution reacting is same as water for many solutions this is not quite true, but (generally) the error this causes is very small) |
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Limitation of calorimetry experiments in school lab |
- Poor precision of usual lab thermometers. Usually these can only be read to the nearest 0.5 degrees, and if the temperature changes is only a few degrees, the percent error is huge. Serious calorimetry needs thermometers with a precision of at least 0.1 degrees |
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How can the quantity of heat energy(in joules) absorbed or released when changes occur be measured? |
The quantity of heat energy (in joules) absorbed or released when changes occur can be measured by a calorimeter. This consists of an insulated vessel in which a measured quantity of water is either warmed or cooled by the change being studied. |
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Write aim and method - measure the heat of solution |
Aim: to compare the heat of solution in water for two substances - ammonium nitrate and sodium hydroxide Method: - approx. 10g ammonium nitrate - approx. 10g sodium hydroxide - polysterene cups (2) - electronic balance - 100mL measuring cylinder - thermometer |
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Measuring the heat of solution Procedure: + safety |
SAFETY: Wear safety glasses. Sodium hydroxide is corrosive so avoid contact with skin. If contact occurs wash well with soap and water 1. Calculate the mass of 0.1 mole of ammonium nitrate, NH4NO3(s) 2. Add approximately this mass to an accurately weighed polystyrene cup and accurately re-weigh it. Record the exact mass of NH4NO3 3. Add exactly 100mL of distilled water to the measuring cylinder and measure its temperature. Record this value 4. Pour the water into polystyrene cup and stir with thermometer until all the solid has dissolved. Record the lowest or highest temperature reached 5. Use a new polysyrene cup and repeat this process using 0.1 mole of solid sodium hydroxide |
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Aim for 'comparing the solubility of different substances in water' - equipment - safety procautions |
Aim: To determine what type of substances are soluble in water Equipment: - test tubes (one for each solute) - pipettes or droppers - numerous substances to determine solubility of -distilled water - test tube rack - spactula SAFETY: Wear safety glasses. Iodine is harmful so avoid contact with skin. If contact occurs wash thoroughly with soap and water. All organic solvents such as kerosene, ethanol and hexane are poisonous to different degrees. Ensure that room is weel ventilated and avoid breathing vapours. Do not use near open flames as these chemicals are flammable. Do not dispose of hexane or kerosene down the skin |
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Procedure for 'comparing the solubility of different substances in water' |
Procedure: 1. Add 2-3 mL distilled water to each test tube 2. Add approximately 0.1 - 0.2 g of sodium chloride to one test tube and shake gently. Record your observations 3. Repeat this procedure with each of the test substances |
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Aim for 'precipitation reactions' - safety procedures |
Aim: To compare the solubility of a range of ionic substance through precipitation reactions Equipment: - test tubes(6) - test tube rack - cations (all 0.1mol L-1) in dropper bottles - Anions (all 0.1 mol L-1) in dropper bottles Safety: Wear safety glasses. Lead an barium salts are poisonous so avoid contact with skin. If contact occurs wash throughly with soap and water. Dispose of as directed by your teacher. Consult 'chemical safety in schools' booklet (CSIS) |
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Procedure for 'precipitation reactions' |
Procedure: 1. Put a 5mL of chemical containing each anion into each of six test tubes. Take care not to mix droppers 2. Add 5mL of chemical containing the first cation to each. Record your observations 3. Clean all test tubes thoroughly as incorrect results can arise from contamination of solution 4. Repeat steps 1 to 3 for the next cation. Continue until all cations have been tested. |
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What is density? |
Density of water: The density of a material is its madd per unit volume and is given by, Density=mass/volume - when the volume solidifies the molecule rearranges in the crystal structure, thereby taking up more room. So the volume increases |
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Is ice or water more dense, explain |
Density of ice is less than that of water. - as the temperature of water drops from room temperature to 4 degrees liquid water becomes denser, just like other substances. The density increases as the molecules become more closely packed. - ice floats on water |
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What is boiling elevation |
- boiling point of a liquid is raised when another compound is added - a solution has a higher boiling point than a pure liquid e.g. salty water =higher boiling point than pure water - called boiling elevation - adding solutes also can decrease freezing point - common antifreeze is car radiators is ethylene glycol. |
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Types of molecular structure + reason |
- Electrons spatially(large amount of space) arrange themselves as far apart as possible to minimise repulsion between the electrons - tetrahedral (methane) - trigonal pyramidal (ammonium) - bent (water) - linear (hydrogen fluoride) - shape of molecule depends on the elements joined together and the distribution of the electrons |
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Differentiate between intramolecular forces and intermolecular forces |
Intramolecular forces: - covalent bonds within molecules are strong and are only broken in chemical reactions. These covalent bonds are also called intramolecular(inside the molecules forces) Intermolecular forces: - weak attractive forces between seperate molecules - when a compound has strong intermolecular forces then the separation of the individual is more diffcult and the melting and boiling points of the compound are raised - Three types of intermolecular forces: - dispersion forces - dipole-dipole forces - hydrogen bonding |
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What are dispersion forces: |
Dispersion forces: - caused by attraction between negatively charged electrons of one molecule and the positively charged nuclei of the atoms of another molecule - the larger the molecule, the greater this attraction. The dispersion forces are greater, the larger the surface area of the molecule |
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Dipole-dipole forces: |
Non-polar bonds - when covalent bonds form between the same element, for example oxygen(O=O), the bond is non polar as the electrons are shared equally - Hydrogen H-H and Nitrogen also have non-polar bonding |
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What are polar bonds |
When covalent bonds form between different elements there is unequal sharing of electrons, one electron get the greater share of electrons - chlorine is more electronegative than hydrogen, so when a pair of electrons is shared in gaseous HCI, the CI atom has a greater share of the electrons - this makes the CI atom slightly negatively charged, and the H slightly positive - bond polar due to unequal charge distibution - degree of polarity depends on electronegativity between the two bonded atoms |
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Polar molecules |
- greater attraction between molecules - caused by attraction between slightly postive part on one molecule and slightly negative part of different molecule - intermolecular force call dipole-dipole force - these substances have higher melting and boiling points |
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Non-polar molecules: |
- Sometimes dipoles of polar bonds cancel due to symmetry in the molecule - carbon dioxide is a linear molecule and the two dipoles cancel - oxygen and hydroxide are also non-polar molecules and these elements have only dipole bonds - water molecule has two polar O-H bonds, molecule is bent and dipoles do not cancel - therefore water is a polar molecule and has dipole-dipole forces between the individual molecules |
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Hydrogen bonding |
- Water has hydrogen bonding - Special type of attraction between slightly positive H atoms in one water molecule and the very electronegative O atom in another water molecule - strongest type of intermolecular force, stronger than other dipole-dipole interactions - occurs where hydrogen is bonded to F,O or N as these are small electronegative elements |
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Effects of intermolecular forces on water are due to: |
- density changes with temperature - ice floats on water - many insects can walk on water - a lot of heat is needed to melt ice and boil water - a droplet of water has an almost spherical shape and so on |
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Solubility of ionic substances: |
Soluble - All group 1 - All NH3 and NH4 except silver - All barium except silver and mercury - All iodine except silver, mercury,lead - All sulfates except mercury, lead,barium, strontium - All CH3OOH - All Nitrate Insolubleions: - All carbonates except for ammoniumand group 1 which are water soluble - All phosphate except group 1 - All hydroxides except ammonium andbarium - All sulfides except group 1 and 2ions and ammonium All oxides except groups 1 ions, ammonium,barium and calcium and strontium |
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name of ion and formula |
ammoniumnitrate NH4
hydroxideion OH-1 nitrate ionNH3-1nitrite ionNH2-1 sulfite ionSO2-3 sulfate ionSO3-4 carbonateion CO3-2 hydrocarbonateion HCO3-1 Phosphateion PO4-3 Acetate ionCH3OOH-1 |
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Investigating some of the properties of water SURFACE TENSION: - aim - equipment - method |
Aim: To investigate the surface tension of water, by comparing it to different surface tensions of water: Equipment: - 5 cent piece - eyedropper - water - water with detergent added - methylated spirits 1. Using the eyedropper see how many drops of water can be place on the coin without the water flowing over 2. Repeat separately with detergent - water mixture and methylated spirits 3. Put them in order from least drops to most drops |
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Investigating some of the properties of water: SURFACE TENSION: - equipment - procedure |
Equipment: - test tube - water - eyedropper - paper clips Procedure: 1. Fill the test tube with water until it nearly overflows 2. Carefully add the paper clips one at a time to the test tube until the water overflows 3. Count how many can be added until it overflows 4. Describe what happens to the water level |
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Investigating some of properties of water: VISCOSITY: - equipment - procedure |
Equipment: - 30 cm long piece of board - waxed paper - water, glycerol, honey, acetone(or nail polish remover), lubricating oil - eyedroppers - stopwatch Procedure: 1. Cover the board with waxed paper 2. Draw a starting line at the top and a finishing line at the bottom of the paper. (About 15cm between the two lines is a good distance) 3. Place the board on an angle of 45 degrees 4. Place a drop of one liquid at the line on the top of the board 5. Time how long it takes for the drop to move from the starting line to the finishing line 6. Repeat the experiment with one drop of each of the different liquids 7. Place the liquid in order from the fastest to the slowest |
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Investigating the effect of salt on the boiling point of water - aim - equipment - Procedure |
Aim: To investigate the change to the boiling point of water when salt is added Equipment: - 250mL beaker - 50g sodium chloride - Bunsen burner - Tripod and gauze mat - Retort stand, boss head and clamp - Matches - Thermometer - Scales - distilled water - Beaker tongs Procedure: 1. Weigh five 10 g samples of sodium chloride. 2. Measure 150cm3of distilled water into a beaker. 3. Heat the beaker of water using a Bunsen burner, using the thermometer as a stirrer to make sure thatthe energy is evenly distributed throughout the liquid. 4. Continue heating the water until the temperature does not increase any more. When this point isreached take the beaker off the heat. Allow the water to cool slightly and then heat up again, recordingthe highest temperature reached. Repeat one more time giving a total of 3 readings for the boilingpoint of distilled water. Record in a table together with any observations. 5. To the beaker of water add 10g of salt, stir to dissolve and mix thoroughly. 6. Place the solution back onto the Bunsen burner, continue mixing and record the highest temperaturethat it reaches. |
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Experiment: Preparing and dilution solutions - aim - equipment - procedure |
Aim: To prepare a solution of known concentration and dilute it to a specified concentration Equipment: - approx. 0.1g potassium permanganate - 250mL beaker - 25mL volumetric flasks (4) - 25mL pipette - stirring rod - filter funnel - water Procedure: 2. Add just enough water to dissolve the crystal of potassium permanganate and transfer the solution to a 250mL volumetric flask 3. Fill the flask to the 250mL mark with water and mix throughly 4. Complete the table for this first solution (solution 1) 5. Pipette 25mL of the first solution into a clean volumetric flask and fill to 250mL 6. Complete the table for this second solution (solution 2) 7. Repeat steps 5 and 6 using the second and third solutions so you have successive dilutions (solutions 3 and 4) |
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Experiment: Investigating the density of water and ice |
Density = mass(g)/volume(mL) Equipment: - 100mL beaker - wide diameter measuring cylinder - electronic balance - distilled water - ice cubes - 10mL pipette - forceps or glass rod - thermometer 1. Accurately measure the mass of the empty beaker. Record this in the table below 2. Add a known volume of distilled water (use the pipette) to the beaker and reweigh. Record this in the table 3. Measure the temperature of the water 4. Repeat this procedure until you have at least 5 measurements (use 10mL increments from the starting volume). Record all measurements in the table |
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What is dissolution |
- When an ionic compound such as NaCI dissolves in water, it dissociates into ions - When covalent molecules dissolve in water, there are no change to the molecule unless they form ions the rate at which dissolution occurs depends on: - the nature of the compound - the temperature of solution - stirring or shaking - how finely divided the solution is |
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How can molarity be measured? |
the molarity of a solution is the number of moles per liter of solution(concentration) molarity = number of moles of solute/number of liters of solution or c=n/V |
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Explain endothermic and exothermic reactions: |
Endothermic: Reactants: Have less heat Products: Have more heat (because they absorb heat during reaction) 'delta H' = products - reactants = more - less = +ve Exothermic: Reactants: have more heat Products: have less heat (release heat during reaction) 'delta H' = products - reactants |
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How check for the following: - reliability: - accuracy: |
Validity: How correct is your method and conclusion Reliability: - If repeated, you should get the same results - not reliable as it was done only once Accuracy: - Only for results - when compared with reported values ti should be similar results |
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What are: - independant variables - dependant variables - controled variables |
Independant variable that is manipulated to determine the value of a dependent variable s
Dependent variable is what is being measured Controlled |
