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AS and A Level: Physical Chemistry

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The dynamic equilibrium and 'Le Chatelier Principle'

  1. 1 Le Chatelier Principle states “If a system that is in dynamic equilibrium is subjected to a change, the position of equilibrium will shift to minimise that change”. Put simply- if you do something, the system will try and reverse what you’ve done!
  2. 2 Adding a catalyst does not change the concentration, pressure or temperature of a system. Therefore adding a catalyst has no effect on the position of equilibrium.
  3. 3 If you increase the concentration of one side of an equation, the position of equilibrium will shift to the other side (to try and return the concentration back to its original value).
  4. 4 If you increase the pressure of the system, the position of equilibrium will shift to the side of the reaction with less moles of gas (to try and reduce the pressure back to its original value).
  5. 5 If you increase the temperature the position of equilibrium will shift in the direction of the endothermic reaction (to try and reduce the temperature back to its original value).

Top equations for acid / base chemistry (A level only)

  1. 1 For a strong acid the acid concentration is equal to the H+ concentration. This is because strong acids fully dissociate their H+ ions. [acid] = [H+]
  2. 2 For a weak acid, because they only partially dissociate their H+ ions, to find the H+ concentration we must use the following equation: [H+] = √ka[acid]
  3. 3 For a buffer, we calculate the value of H+ by using: [H+] = Ka[acid] / [salt] (where Ka is the acid dissociation constant)
  4. 4 For a strong base, we calculate the H+ value by using: [H+] = Kw / [base] (where Kw is the ionic product of water = 1 x 10-14)
  5. 5 To convert [H+] into pH, we would use the equation: pH = -log[H+]

Top tips for ionisation energy

  1. 1 One of the factors which will affect ionisation energy is electron shielding. This is how many inner shell electrons an atom has. The more electron shielding, the lower the ionisation energy. Electron shielding stays the same across a period and increases down a group.
  2. 2 The second factor affecting ionisation energy is the proton number / nuclear charge. The higher the nuclear charge the higher the ionisation energy. Nuclear charge increases across a period and down a group.
  3. 3 The third factor affecting ionisation energy is the atomic radius (size of the atom). The higher the atomic radius the lower the ionisation energy. Atomic radius decreases across a period (as the increased number of protons pulls the electron shells closer) and increases down a group.
  4. 4 All three of these factors combine to have an effect of increasing the ionisation energy as we go across a period (eg F has a higher ionisation energy than O)
  5. 5 All three of these factors combine to have an effect of decreasing ionisation energy as we go down a group (eg K has a lower ionisation energy than Na)

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  1. Peer reviewed

    Investigate the Properties of Ionic and Covalent substances

    3 star(s)

    Apparatus/Materials: Sodium Chloride Test Tubes Sucrose Glass Rods Naphthalene Beaker (2- 100cm3) Copper (II) Sulfate Battery Calcium Carbonate Connecting wires Calcium Oxide Electrodes Spatulas Bunsen burner Tongs Method(1): Heating Substances Approximately two spatulas of sodium chloride was placed into a test tube and its contents were gently heated at first then heated strongly until no further change occurred.

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    Gas Behaviours and the Weather

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    Air pressure also relates to the density of the air and the height above the Earth's surface from where it is being measured (see Passante, 2006). The lines on the weather map (Fig. 1) represent the variations in pressure from region to region shown in 'isobars'. Temperature is a measurement of the speed of the molecules' movement in a substance. The more energy the molecules have, the faster they move and the higher the temperature is. When measuring the temperature of the air, it is the speed of the molecules that is being measured (Bureau of Meteorology, 2010).

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    The Electromagnetic Spectrum White light (what we call visible or optical light) can be split up into its constituent colours easily and with a familiar result - the rainbow. All we have to do is use a slit to focus a narrow beam of the light at a prism. This set-up is actually a basic spectrometer. The resultant rainbow is really a continuous spectrum that shows us the different energies of light (from red to blue) present in visible light.

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    Atmospheric Pollution

    3 star(s)

    The output pollutants produced by coal fired stations are, sulphur oxides, nitrogen oxides and carbon dioxide. Sulphur is found in coal. When coal burns the sulphur compounds are oxidised so convert into sulphur oxide gases. Nitrogen oxide emissions can be produces in two ways. Firstly, most fuels contain compounds of nitrogen as it is formed by proteins. When nitrogen combusts, the nitrogen compounded are oxidised giving us NOx gases. The other way is that at high temperatures of combustion atmospheric nitrogen and oxygen combine to produce thermal NOx gases. Carbon dioxide is formed by the carbon in the coal reacting with the oxygen, making carbon dioxide when combusted.

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    Chemical Bonding

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    The energy required to remove electrons from metals to attain a noble gas structure is considerably low. Ionic bonds also occur in non-metal atoms which gain electrons the reason for this is the group 7 atoms have a strong electron affinity. Covalent Bond A covalent bond is formed by the sharing of valence electrons rather than by transfer, the bonds are formed between non-metal atoms. An example of this is hydrogen. Hydrogen atoms have one outer electron. In the hydrogen molecule each atom contributes one electron to the bond.

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    How does aspirin work?

    3 star(s)

    Salicin was concerted into Salicylic acid by the Italian chemist Piria in 1839. It was synthesised by a process discovered by Kolbe and Lautemann in 1860 which led to the introduction of Salicylic acid and sodium salicylate (forerunners of aspirin) for treatment of fever and arthiritis. However, these compounds were toxic to the stomach and caused diarrhoea and vomiting. German chemist Felix Hoffmann was set the task by Arthur Eichengrun of Friedrich Bayer & Co in 1893, to find a less toxic alternative.

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  7. Use available evidence to gather and present data from secondary sources and analyse progress in the development and use of a named biopolymer.

    Biopolymers A biopolymer is a naturally occurring polymer generated using natural resources like plants and micro-organisms. Biopolymers are polymers that are generated from renewable natural sources, are often biodegradable, and not toxic to produce.4 Starch, proteins and peptides, DNA, and RNA are all examples of biopolymers, in which the monomer units. The polymer primary structure is the chemical composition and the sequence in which these units are arranged in. Many biopolymers spontaneously "fold" into characteristic shapes, which determine their biological functions.2 Biodegradability and other plastic properties strongly depend on the polymer structure.

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  8. Electrolysis of Aqueous and Molten Ionic substances

    The anion is attracted to the anode, and the cation is attracted to the cathode. The electrolyte is the substance which undergoes electrolysis. The current flows from the cathode to the anode. The electrons are pumped to one of the electrodes, which is the cathode (so it is negative), and away from one electrode, which is the anode (so it is positive). So the cathode is full of electrons, so cations (positive ions) go there to gain electrons, get reduced. And the anode has less electrons, so anions (negative electrons) go there to loose electrons, get oxidised.

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  9. Science at Work Research . Dulux Paints, a Hospital, a leisure centre and a GPs surgery.

    Exterior products: Products made for exterior: Main range: non-drip gloss, professional liquid gloss. Once: Gloss. Weathersheild: smooth masonry paint, textured masonry paint, ready to roll smooth masonry paint, exterior gloss, exterior satin, exterior one coat gloss, exterior undercoat, exterior stablishing primer, multi-surface fungicidal wash, exterior preservative primer. What Science is involved? Paint is manufactured with mineral fillers (clay and limestone) and pigments from various minerals. Paint contains four basic ingredients pigments, resin solvents and additives. Each has a different purpose. The pigment is for colour, resin is a binder, the solvent carries the pigment and resin from the paintbrush to the wall, the additive is added to change or improve its characteristics, in paint it is added to help the paint stick better.

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  10. In this experiment, the rate of decomposition is calculated by measuring the volume of the product gas using water displacement.

    The reaction can be described as follows: 2 Co2+ (aq) + ClO- (aq) + 2H2O (l) --> Co2O3 (s) + 4 H+(aq) + Cl-(aq) Purpose The objective of this experiment is to determine the rate of decomposition of bleach by measurement of gas production at several different temperatures. Hypothesis The decomposition rate will increase if the surrounding temperature increases. If the surrounding temperature increases by 10�C, the reaction rate will double. If the temperature decreases by 10�C, then the reaction rate will decrease by half.

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  11. Antacid Lab. Are name brand antacids better than generic brand antacids to neutralize stomach acids that may cause diseases? Which antacid is more effective? Are both brands equally effective?

    Brand name antacids may be a bestseller compared to generic brands due to advertising and seemingly low prices. However it is questionable if brand name antacids are more effective that generic brand antacids. They may even be equally effective but people are not aware of the fact because generic brands are not well known before a crowd. It is important for people to know which brand they must use especially if one is stronger and may act quickly than the other.

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  12. Finding the energy given off from various fuels

    Place the Logger Pro inside of the can 4. Light the spirit burner of the fuel under the can. 5. Close the container around the ring stand and the spirit burner 6. Stir the Water inside of the can constantly. 7. Record the temperature of the water for 3 minutes. 8. Repeat the steps for each type of fuel. 9. Find the number of kilojoules released by each of the fuels 10.

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  13. Determination of Ksp of copper(II) iodine by emf measurement

    Zn Zn2+ + 2e- Cu2+ + 2e- Cu ? n=2 For the Zn(s)/Zn2+(aq) half-cell, = -0.76V For the Cu(s)/Cu2+(aq) half-cell, Ecell = ER - EL = {(+0.34) + 0.0295 log [Cu2+(aq)]} - {(-0.76)} = (1.10) + 0.0295 log [Cu2+(aq)] When the voltage of the cell system is measured, the concentration of Cu2+ can be determined by the above equation. Therefore, the solubility product can be calculated by the above principle. Purposes: To determine the solubility product of copper(II) iodate(V)

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  14. Analysis of Oxygen Absorber. How can the oxygen absorber absorb oxygen in the food package? What is the composition of the oxygen absorber? In this activity, we will plan and carry out an investigation to find out the chemical nature of the oxygen absorb

    Besides, oxidation of food can cause the colour change of food. If the colour of foods changes, people will have a lower longing to have these food. Using oxygen absorber can prevent the change of colour. When people discovered that oxygen can be the main cause of degeneration of food, scientists started to find out the solutions. This caused the fast development of oxygen absorber in the 20th century. Scientists combined two simple ideas: "Irons absorbs oxygen when it rust." and "Prevent oxidation by eliminating oxygen.", and then iron powder package was first acted as oxygen absorber.

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  15. Analysis of Two Commercial Bleaches

    first, then one was washed by potassium iodide solution, one was washed by sulphuric acid), 1 pipette filler, 2 250cm3 volumetric flasks (Washed by deionized water only), 1 conical flask (Washed by deionized water only), 1 burette (Washed by deionized water first, then washed by standard thiosulphate solution), 1 washing bottle (Filled with deionized water), and 1 dropper Reagents used: "Kao" Bleach, "Clorox" Bleach, 1.0 M potassium iodide solution (KI), 1.0 M sulphuric acid (H2SO4), Standard thiosulphate solution(S2O32-) with conc.

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  16. Determining an equilibrium constant. The aim of this experiment is to calculate the equilibrium constant (kc) of the reaction: CH3CO2C2H5(l) + H2O(l) C2H5OH(l) + CH3CO2H(l)

    For part B: 5 conical flasks, deionized water, a few cm3 of phenolphthalein, burette with stand, about 150 cm3 of approximately 1M standard sodium hydroxide solution Procedure: Part A Step 1. 5 boiling tubes were labeled with 1A, 1B, 2, 3 and 4 respectively and their corresponding stoppers were also labeled as the same as their boiling tubes. 2. Each stopper was wrapped with plastic films. 3. Each tube with its stopper was weighed using an electronic balance. 4. 5.0 cm3 of 2M hydrochloric acid were added to each tube.

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  17. The titrimetric determination of the concentration of sodium hydroxide

    The scale can be read to an accuracy of half a division e.g. to 0.05 cm3. Bulb Pipette: used to deliver an accurate volume of a solution. This can be 10cm3 or 25 cm3. Conical flask: used to hold chemicals and to make chemicals, substances can be stirred and swirled without the risk of spilling and reduces the loss of the evaporation due to the narrow neck. Methyl Orange Indicator: a pH indicator frequently used in titrations. It is often chosen to be used in titrations because of its clear colour change. Titration: The technique of titration is used to find out accurately how much of a chemical substance is dissolved in a given volume of a solution, that is, the concentration of the solution.

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  18. Determination of the content of Mg (OH)2 in an indigestion remedy by back titration

    as stated in the B.P. Key Words Burette: a long vessel with a tap at the bottom which is used to measure accurately the volume of a solution added. The scale can be read to an accuracy of half a division e.g. to 0.05 cm3. Bulb Pipette: used to deliver an accurate volume of a solution. This can be 10cm3 or 25 cm3. Conical flask: used to hold and to make chemicals, substances can be stirred and swirled without the risk of spilling and reduces the loss of the evaporation due to the narrow neck.

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  19. Separation of Amino Acids by Paper Chromatography

    Assume that the edges of chromatographic paper are not touch the sides of the beaker since the solution at edges will move faster due to capillary action. The spots will bend and Rf value is affected 3. Assume that the beaker is saturated with the solvent before putting the chromatographic paper inside. As the atmosphere is not saturated, there is a diffusion gradient between chromatographic paper and air, some solvent may vapourize from chromatogram and result in long tail of spots. 4. Assume that the temperature remains constant, as the temperature may affect Rf values.

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  20. The iodination of propanone is a reaction with interesting kinetics. The reaction is acid-catalysed.

    One can say that [CH3COCH3] is effectively constant, and so that b can be found. Solutions of known concentration of (a) propanone, (b) iodine in potassium iodide, and (c) an acid buffer of known pH are prepared and brought to the required temperature in a thermostat bath. The reaction is started by pipetting volumes of the three solutions into a flask, and a stop watch is started. After a few minutes, a sample of the reacting mixture is pipetted from the solution into a sodium hydrogencarbonate solution.

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  21. Experiment Objective. To determine the approximate strength of hydrogen bond formed between ethanol molecules by measuring the enthalpy change on mixing it with cyclohexane.

    4.> A thermometer is then put into the test-tube. 5.> Pipette 4 cm3 of ethanol into the test-tube. 6.> Pipette about 9 cm3 of cyclohexane into the same test-tube. 7.> The mixture is stirred gently & carefully with the thermometer and the lowest temperature is recorded. Results Mass of the test-tube: 14.44 g Table 1 shows the temperature change after mixing two substances: ethanol cyclohexane test-tube Initial temperature /? 15.5 16.5 18 Lowest temp. after mixing /? 13.8 ?T /? - 1.7 - 2.7 - 4.2 Table 2 shows the data of the substances: Molecular mass Density /kgdm-3 Specific heat capacity kJkg-1K-1 Volume of solution added /cm3 ethanol 46 0.81 2.44 4 cyclohexane 84 0.78 1.83 9 test-tube / / 0.78 / Energy absorbed to break hydrogen bond = energy absorbed from test-tube (E1)

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  22. Acid-base titration. Objective To determine the concentration of sulphuric acid (H2SO4) using sodium carbonate (Na2CO3) as the primary standard in volumetric analysis.

    Filter funnel x 1 Dropper x 1 50.0 cm3 burette x 1 Stand x 1 Burette clamp x 1 White tile x 1 Procedure A. Preparation of Standard Sodium Carbonate Solution 1. The mass of the weighing bottle was weighed using an electronic balance. 2. Sodium carbonate was added to the weighing bottle carefully with a spatula. The mass of the weighing bottle with sodium carbonate was weighed. The masses weighed were recorded. By weighing by difference, 1.3 g of sodium carbonate could be measured accurately. 3. The weighed sodium carbonate was poured into a clean dry 100 cm3 beaker.

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  23. Objective: The purpose of this experiment is to determine the composition of a mixture of solutions of NaOH and Na2CO3 by double indicator method.

    and Na2CO3(aq). Solution mixture of reaction (1) at the equivalence point is alkaline, while that of reaction (2) is acidic and that of reaction (3) is neutral. Therefore the whole titration should have three breaks in the pH curve, corresponding to the above three stages. Reactions (1) and (3) can be indicated by phenolphthalein and that of reaction (2) can be indicated by methyl orange. III. Procedure: 1. All apparatus should be rinsed properly with corresponding solution 2. 25cm3 of the mixture of NaOH(aq) and Na2CO3(aq) was pipetted into conical flask. 3. Burette was filled with standardized 0.1M hydrochloric acid 4.

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  24. Objective : To determine the concentration of an unknown diprotic acid using acid-base titration.

    Since the products of an acid-base reaction may be acidic, basic or neutral, it is important to choose an indicator so that the end point matches the equivalence point. An appropriately chosen indicator will show a colour change(end point) when the reaction is complete(equivalence point). For example, phenolphthalein, an acid-base indicator turns pink in neutral or slightly basic solutions. When a very slight pink colour is seen in the presence of phenolphthalein, equimolar amounts of acidic protons and base are present.

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  25. Explain what is meant by the following terms: i) Oxidising agent: ii) Displacement reaction: iii) Electronegativity

    Though their ability and strength as oxidising agent alters as the group is descended- more on this later. Oxidising agents become reduced in the process of a reaction. Take the following reaction as our example: 2 Na + Cl2 = 2 Na Cl 2 Na + Cl2 = 2 Na Cl 0 0 +1 -1 0 = neutral oxidation state, uncharged. +1 = the oxidation state has risen, Na has become oxidised -1 = the oxidation state has reduced, Cl has become reduced Therefore, because chlorine has been reduced, it has accepted electrons from the sodium, it is said to

    • Word count: 1717

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