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AS and A Level: Physical Chemistry

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Meet our team of inspirational teachers Get help from 80+ teachers and hundreds of thousands of student written documents 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)

1. Quantitative Determination of Food Colouring in Jelly Crystals using UV/Vis spectroscopy

The absorption in the visible range affects the perceived colour of chemicals used in food products involved. In this region of the electromagnetic spectrum, molecules undergo electronic transitions from the ground state to the excited state The Beer-Lambert law states that the absorbance of a solution is directly proportional to the concentration of the solution and the path length. Thus, for a fixed path length, UV/VIS spectroscopy can be used to determine the concentration of a solution. It is necessary to know how quickly the absorbance changes with concentration. Therefore the equation used is A=Ecl where A is the absorbance, E is the molar extinction coefficient, c is the sample concentrations in moles/litre and l is the length of light path through the sample.

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2. Objective:-To prepare a buffer solution and observe the properties of a buffer

On the other hand, if a small amount of base is added to the solution, CH3COOH(aq) will react with the base, giving out salt i.e. CH3COONa. This shifts the equilibrium of CH3COONa (aq) CH3COO- (aq) + Na+ (aq) to the right. The increase of [CH3COO-] does not contribute to any change in pH. Therefore, the pH of the solution remains almost constant. Procedures Preparation of Solution A(Buffer) 1. The pH meter was calibrated with a buffer of pH 10. 2. 25 cm3 of 0.1M NaOH was measured with a measuring cylinder and poured into a 100 cm3 beaker.

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3. Analysis of 2 commercial brands of bleaching solution & a determination of the best buy

4. Titrate this mixture against the standard sodium thiosulphate solution provided. Add starch indicator when the solution become pale yellow. 5. Record your results and calculate the molarity of the orginal bleach solution. 6. Determine which bleach has the lowest price per mole of actual bleach. Results : Brand A = ___________KAO_____________ Brand B = _________Best Buy____________ Volume = ___________1.5L______________ Volume = ____________2L_______________ Price = _______\$12.9 / Bottle____________ Price = ________\$10.9 / Bottle____________ Mole = _________0.753 Mol_____________ Mole = ___________1.152 Mol ___________ \$/mole = _______\$17.13 / Mol ___________ \$/mole = __________\$9.46 / Mol__________ Best buy is ________ Best Buy___________ Titration of Brand A against the standard sodium thiosulphate solution Titration 1 2 3 4 Final Burette Reading (ml)

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4. Analysis of Commercial Vitamin C Tablets

Procedures : 1. Accurately weigh out 0.6 to 0.7g of potassium iodate(V). Record the mass.. 2. Dissolve this in deionized water and make up to 250 cm3 in a volumetric flask. 3. Use such iodate(V) solution to standardize the given thiosulphate solution as follows : (a) Pipette 25.0 cm3 of KIO3(aq) into a conical flask, add to it about 5 cm3 of 1 M KI(aq) followed by about 10 cm3 of 0.5 M H2SO4(aq) , then immediately titrate with 0.05 M Na2S2O3(aq)

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5. Analysis of Sulphur Dioxide Content in Wine

In this experiment, the amount of total available SO2 in the wine, irrespective of its actual form in the sample is determined. The method involves first the conversion of all SO2 into SO32-. Acidification of the solution then liberates all SO2 : SO32-(aq) + 2 H+(aq) --> SO2(aq) + H2O(l) SO2 is then titrated with iodine solution : SO2(aq) + I2(aq) + 2 H2O(l) --> 2 HI(aq) + H2SO4(aq) Chemicals : White wine (non-sparkling or non-carbonated), 1M NaOH , 2M H2SO4 , 0.005M I2 , KIO3 , Starch solution (freshly prepared)

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6. Order of Reaction between Iodine and Propanone

312 608 933 1205 1507 1791 Volume of Na2S2O3 added (cm3) 20.10 20.00 19.70 19.30 18.20 17.80 Questions: 1. Write a balanced chemical equation to represent the reaction between iodine and propanone in acidic medium. 2. What is the function of the sodium hydrogencarbonate? Sodium hydrogencarbonate solution is used to quench the reaction in this experiment. When the reaction mixture is transferred into the conical flask containing sodium hydrogencarbonate solution, it neutralizes the sulphuric acid in the reaction mixture. 2NaHCO3 + H2SO4 --> Na2SO4 + 2CO2 + 2H2O At room temperature, without the presence of hydrogen ions (catalyst), the rate of the reaction between propanone and iodine is extremely slow and is practically stopped.

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7. SIMPLE CALORIMETRY TO FIND THE ENTHALPY OF COMBUSTION OF ALCOHOLS

i.e. temperature increased of water, mass of water, specific heat capacity of water, mass of the alcohol used and molar mass of the alcohol are needed to collect to work out the enthalpy of combustion of the alcohol. Chemicals Ethanol, ? = -1367 kJ mol-1 Propan-1-ol, Butan-1-ol Materials and apparatus Safety spectacles 12-oz. aluminium beverage can with cut out top Bench mat Digital balance (to 0.001g) Stand, boss, clamp Spirit burners Thermometer 100 cm3 measuring cylinder III. Data Combustion of Ethanol: Final Initial Temperature increase Temperature of water: 36.0?

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8. To Estimate the Purity of Commercial Nitrite

The sodium nitrite powder was dissolved in distilled water in volumetric flask of 250cm3 where the molarity was about 0.05M. 3. 25cm3 0.02M potassium permanganate solution was pipette into a conical flask, 15cm3 dilute sulphuric acid was added for acidification. 4. Sodium nitrite solution was transferred to burette for titration. 5. The initial burette reading was taken. 6. Sodium nitrite solution was slowly added to the acidified permanganate solution with continual swirling until the colour of the permanganate solution was just become colourless.

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9. The order of the decomposition of hydrogen peroxide

24.05 10 43.55 25.20 18.35 15 16.45 1.60 14.85 20 28.30 16.45 11.85 25 37.35 28.30 9.05 30 44.40 37.35 7.05 Let Vo cm3 be the potassium permanganate solution required for the oxidation of hydrogen peroxide at the beginning of the reaction to, and Vt cm3 required after

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10. Analysis of Brick cleaner Aim: To find the percentage by mass of hydrochloric acid present in brick cleaner by doing an acid-base titration.

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11. To study the effect of dilution, concentration of water and temperature on the rate of the chemical reaction between methanal (HCHO), sodium sulphite (Na2SO3) and sodium hydrogensulphite (NaHSO3).

3. 2 drops of phenolphthalein were added into the boiling tube. 4. 5.0 cm3 of solution B was measured using another clean 10.0 cm3 measuring cylinder and was poured it into the boiling tube. 5. The stop watch was started immediately. 6. The reaction mixture was quickly stirred with a clean and dry glass rod. 7. Any colour change was observed against a white tile. 8. The time for the pink colour to appear was recorded in Table 1. 9. The boiling tube was washed. 10. Steps 1-9 were repeated for the other sets of experiments mentioned in step 1. 11. A graph of volume of water added was plotted against time.

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12. Aim: To determine the conecentrations of hychloric acid and ethanoic acis by thermometric titration and find the enthalpy of neutralization.

The procedure was the same as HCL except CH3COOH was used. Results and Calculations: (I) Titration of HCL Volume Added/ cm3 1.0 5.0 10.0 15.0 20.0 25.0 30.0 35.0 40.0 45.0 50.0 Temp /oC 25.0 27.5 28.5 30.0 30.5 31.0 30.0 29.0 28.5 27.5 22.5 (II) Titration of CH3COOH Volume Added/ cm3 0.0 5.0 10.0 15.0 20.0 25.0 30.0 35.0 40.0 45.0 50.0 Temp /oC 23.0 24.5 24.5 24.5 24.5 24.5 24.5 24.5 24.5 24.0 24.0 Calculations: 3. Concentration of HCl: (1)(50) = m (25) m = 2M Concentration of CH3COOH: (1)(50) = m (5) m = 10M 4. By E=mc?T For HCL: E = [(100)/1000](4180)[(32) - 25] E = 2926 J dm-1 K-1 ?

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13. To determine enthalpy change of hydration of magnesium sulphate(VI)

During the addition, the following occurs: CaCO3(s) + 2H+(aq) --> Ca2+(aq) + CO2(g) + H2O(l) With the help of the data of heat change of the solution mixture, the average heat evolved by one mole of calcium carbonate during the reaction can be calculated. After that, by using a suitable energy-cycle diagram, and applying Hess's law, the heat formation of formation of calcium carbonate can be calculated. 5) Procedure: Please refer to the lab. manual 6) Data: 1st Part: Reaction of calcium with dil. Hydrochloric acid Experiment No: 1 2 Mass of Ca used / g 0.53 0.51 Volume of hydrochloric acid used: 100cm3 2nd Part: Reaction of calcium carbonate with dil.

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14. To study the factors which affect the rate of the methanol clock reaction.

Then a known amount of sodium hydrogensulphate(IV) and sodium sulphate(IV) solution was added to the mixture at different temperature. By measuring the time taken for the color of the solution to tuen pink inder different conditions, factors which determine the rate of the reaction can thus be studied. 5) Procedures: please refer to the lab. manual 6) Observations: (a) After the addition of solutions A and B, the solution mixture changed color from nearly colorless to pink. (b) In part (A), the more color methanol solution used, the shorter time required for the color change of the mixture. (c) In part (B), the hotter the solution used, the shorter time required for the color change of the mixture. 7)

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15. To determine the heat of formation of calcium carbonate

( H2) After that, by constructing a suitable enthalpy cycle, i.e. MgSO4(s) + 7H2O(l) MgSO4 . 7H2O(s) MgSO4(aq) and applying Hess's law, the molar enthalpy change of hydration of magnesium sulphate(VI) ( H) can be calculated. ( H = H1 - H2) 5) Data: Anhydrous MgSO4(s) MgSO4(s)-7-water Molar mass / g mol-1 120.4 246.4 Mass of copper(II) sulphate / g 3.01 6.16 Initial temp. of water / oC (T1) 25 24 Highest/Lowest temp. attained / oC (T2) 34 22.5 Change in temperature / oC (T2-T1)

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16. Enthalpy Change of the Hydration of Magnesium Sulphate

Step 1 to step 15 were repeated but 0.025 mole of magnesium sulphate-7-water was used to replace anhydrous magnesium sulphate. Results Anhydrous MgSO4 Hydrated MgSO4 Initial mass of weighing bottle with magnesium sulphate/ g 13.30 16.74 Final mass of weighing bottle with magnesium sulphate/ g 10.51 10.70 Actual mass of magnesium sulphate added/ g 2.79 6.04 Initial temperature of water / ? 25.00 26.00 Highest/lowest temperature attained/ ? 29.00 24.00 Change in temperature / ? 4.00 2.00 Specific heat capacity of water = 4200 J kg-1K-1, specific heat capacity of polystyrene foam cup = 1300 J kg-1K-1, density of water = 1.0 g cm3 Questions 1.

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17. Comparison of Reactions of Aldehydes and Ketones

Where the product is formed, it separates as white crystals. In the case of ethanal, the equation is: With propanone, the equation is: B: Add either a few drops of the aldehyde or ketone, or possibly a solution of the aldehyde or ketone in methanol, to the a solution of the 2,4-dinitrophenylhydrazine in methanol and sulphuric acid. A bright orange or yellow precipitate shows the presence of the carbon-oxygen double bond in an aldehyde or ketone. The overall reaction is given by the equation: R and R' can be any combination of hydrogen or hydrocarbon groups (such as alkyl groups).

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18. The purpose of this experiment is to examine the flame colour of selected s-block metal chlorides and the solubility of selected Group II metal sulphates and hydroxides.

Discussion Flame colour: Most s - block elements give a characteristic flame colour in the flame test. The test is done by putting a sample of the elements or their compounds into a non - luminous Bunsen flame. Since the outermost shell electrons of atoms of both Groups I and II elements are weakly held by the nucleus, the electrons are easily excited to higher energy levels upon heating. When these electrons return to their ground states, radiation is emitted. For many Groups I and II elements, the emitted radiation falls into the visible light region of the electromagnetic spectrum.

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19. Analysis of vinegar. Comparing the concentration of different samples of vinegar.

The restaurant use Ethanoic acid (vinegar) for preservative and food flavouring. The Ethanoic acid's pH = 3. References: Applied science book and websites: http://en.wikipedia.org/wiki/Acetic_acid, http://chemistry.about.com/od/acidsbases/a/aa082304a.htm and http://en.wikipedia.org/wiki/Sodium_hydroxide Risk assessment: Chemical/instruments Symbols / Concentration Hazard Precaution In case of contact/emergency Sodium hydroxide solution NaOH / 0.100 moldm-3 Fire hazard, poison, danger, Safety goggles, lab coat, avoid contaminate with skin Rinse immediately and seek medical attention Ethanoic acid Standard vinegar Restaurant vinegar Take-away vinegar CH3COOH 22.767 cm3 30.267 cm3 41.867 cm3 Contact with the eyes can cause serious long-term damage Always wear safety glasses. Do not allow the solution to come into contact with your skin.

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20. Chromatography Trail and Investigation

Distilled Water Capillary Tube Ruler Hairdryer Method: 1) First get a ruler and pencil and then a pencil line 1cm from the bottom of the chromatography paper. Put four crosses on the line just made. 2) Using the pencil write the name of each colour dye by the matching spot. 3) Take a Capillary tube and dip it into one of the dyes, using a clean capillary tube for each dye (We do this to make sure that they do not get mixed up). 4) We then get the chromatography paper and place it into the beaker; we then get the distilled water and fill it up to the 1cm line.

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21. Objective: To determine the concentration of a solution of sodium hydroxide by titration against a standard solution of potassium hydrogen phthalate

+ OH-(aq) --> H2O From the above equation No of moles of H+ (aq) = 1 No of moles of OH-(aq) 1 The determination of the concentration of NaOH can be determined by the following equation: Molarity of C8H5O4K � Volume of C8H5O4K = mol ratio of C8H5O4K Molarity of NaOH �Volume of NaOH mol ratio of NaOH Molarity of C8H5O4K � Volume of C8H5O4K = 1 Molarity of NaOH �Volume of NaOH 1 The volume Of NaOH can be determined by the titration result. Results: trial 1 2 3 4 Burette readings Final: 36.9 34.4 34.8 34.4 34.1 Initial: 11.1 8.7 9.5 9.4 8.3 Volume used(titre)/cm3 25.8 25.7 25.3 25 25.8 Mean titre/cm3

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22. Titration. The aim of this investigation was to find out the accurate concentration of an acid solution, which is thought to have a concentration between 0.05 and 0.15mol dm in concentration.

* Funnel * Test tube * Small beaker for waste solution * Wash bottle and distilled water * White tile Making a standard solution The sodium carbonate and sulphuric acid react in a 1:1 ratio. The sodium carbonate solution was made to a concentration of 250cm 0.1 mol dm because this amount is between 0.05 and 0.15mol dm which is thought to be the concentration of the sulphuric acid. The next step was to calculate how much sodium carbonate was needed to make a 0.1 mol dm solution:- First the relative atomic mass of sodium carbonate was calculated: (Relative Atomic Masses: Na = 23, C = 12, O = 16)

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23. Determining activation energy (Ea) of a reaction potassium between peroxodisulphate and iodine

to its early stage when the concentration time curve is almost linear. The Na2S2O3 (aq) acts as a gatekeeper. If Na2S2O3 was absent. After mixing the solution, the reaction will take place immediately. The iodine produced will immediate react with starch to form blue complex .The time taken for the appearance of blue colour of each 5 temp reading will be would be too quick and immeasurable The reaction between peroxodisulphate (VI) ions and iodide ions in solution forms sulphate (VI) ions and iodine. The equation for this reaction is as follows: S2O82- (aq) + 2I- (aq) ? 2SO42- (aq)

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24.  Determining an Equilibrium constant

flame * Keep the stopper on the bottle as much as possible Hydrochloric acid -General Hazards * irritant * wear gloves and safety googles Sodium hydroxide -General Hazards * corrosive * wear gloves and safety googles Special Handling Information * Eye protection (safety goggles) must be worn at all times. * Wear gloves * Avoid skin contact with the chemicals Apparatus and Reagents Used (Part A) * Safety spectacles * 10 specimen tubes with well-fitting caps * Labels for tubes and stoppers * Access to a balance * Pipette, 5 cm3, and safety filler * Dilute hydrochloric acid, 2M HCl * 2 measuring cylinders, 10 cm3 * Distilled water * Ethyl ethanoate, CH3COOC2H5 Procedures :( PART A)

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25. Analysis of commercial vitamin C tablets

De-ionized water was added to reach the graduated mark. 8. 10cm3 of vitamin C solution (with dilute H2SO4) was pipetted into a conical flask 9. 5cm3 of 1M KI solution was added into the conical flask. 10. 25cm3 of standard KIO3 solution was pipetted into the conical flask which contained a mixture of vitamin C, H2SO4 and KI solution. 11. The mixture was then titrated immediately with standard Na2S2O3 solution 12. The steps were repeated for 2 times. Results Standardization of Na2S2O3 solution Weighing :Mass of solid (potassium iodate(V) ) used = 0.6808 g Titration : Burette contained : Na2S2O3 Conical flask contained : KI,KIO3, H2SO4 Burette readings: Volume (cm3)

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