Core Practicals:

Question 1

Core practical 1: Molar Volume of a Gas -> experimental objective

Answer 1

-> to find the volume of one mole of carbon dioxide gas

Question 2

CP1: method

Answer 2

1. Measure 30cm^3 of 1mol dm^-3 ethanoic acid and transfer to a conical flask
2. Attach conical flask to gas syringe or use collection over water method
3. Measure the mass of a weighing bottle with approx 0.05 g of calcium carbonate
4. Add the calcium carbonate to the conical flask- quickly resealing the bung so no gas escapes
5. Measure the final total volume of gas
6. Reweigh the empty weighing bottle test tube from step 3
7. Repeat the experiment several more times, increasing the mass of calcium carbonate by about 0.05 g each time

Question 3

CP1: reaction equation

Answer 3

CaCO3 (s) + CH3COOH (aq) -> CaCl2 (aq) + H2O (l) + CO2 (g)

Question 4

CP1: conclusion

Answer 4

-the molar volume of carbon dioxide at room temperature (298K) is 24.4 dm^3 mol^-1
-molar volume will change depending on the temperature of the gas
-however most molar volumes are determined at standard temperature and pressure 8STP) which are 100 kPa and 298K

Question 5

CP1: key points

Answer 5

-wait until no effervescence is observed before weighing flask containing acid and marble chips (CaCO3) to minimise gas loss
-don’t use too much CaCO3 so you don’t produce more gas than the measuring cylinder can fit
-a weak acid is used so that the reaction is slower, meaning there is less gas loss between adding marble chips and attaching bung
-an alternative method could involve attaching marble chips on a string to the bung, sealing the test tube with a bung, and then tipping the test tube so that the acid comes to the contact with the marble chip -> this could reduce the loss of product

Question 6

CP1: errors

Answer 6

-for syringes, a plunger may not be free moving so may need lubricant
-CO2 is slightly soluble in water, so the exact volume is not measured
-some gas escapes between addition of marbles chips and sealing the test tube
-bung may not be airtight
-transferring the solid -> it is important to weigh the tube containing marble chips before the addition and reweigh after the addition, this method is ‘weighing by difference’ and ensures the amount og CaCO3 that ends up in the reaction mixture is known

Question 7

Core practical 2: Enthalpy Changes using Hess’s Law -> experimental objective

Answer 7

-> to calculate the molar enthalpy change for two reactions and use Hess’s Law to drtermine the enthalpy change for the reactions

Question 8

CP2: safety

Answer 8

-wear eye protection and suitable chemical resistant gloves
-avoid skin contact with reactants and products

Question 9

CP2: method

Answer 9

1. Place approximately 3 g of solid potassium carbonate in a test tube
2. Accurately wigh the test tube and its contents
3. Use a burette to add 30 cm^3 of 2.0 mol dm^-3 dilute hydrochloric acid into a polysterene cup which is supported by a beaker
4. Measure the temperature of the acid
5. Gradually add the potassium carbonate to the acid, stirring and continuously monitoring the temperature
6. Reweigh the empty test tube
7. Repeat steps 1-6 using approximately 3.5 g of potassium hydrogencarbonate and record the lowest temperature reached

Question 10

CP2: errors and assumptions

Answer 10

-energy can be transferred to the surroundings
-specific heat capacity of HCl (aq) assumed to be the same as water
-ignore energy that is absorbed by the polysterene cup
-density of the HCl (aq) assumed to be the same as water

Question 11

Core Practical 3: Finding the Concentration of a Solution -> experimental objective

Answer 11

-> to find the concentration of a solution of hydrochloric acid

Question 12

CP3: safety

Answer 12

-wear eye protection and suitable chemical resistant gloves
-avoid skin contact with acid, alkali and indicator
-always use a pipette filter; never use your mouth to suck the liquid up
-take care when clamping and filling the burette that it does not crack or topple over

Question 13

CP3: method

Answer 13

1. Wash out a 250 cm^3 volumetric flask with distilled water
2. Use the pipette to add 25 cm^3 hydrochloric acid into the volumetric flask and make the rest up with distilled water
3. Pour a 25 cm^3 sample of the HCl solution into the conical flask and add a few drops of phenolphthalein indicator
4. Prepare your apparatus for the titration- sodium hydroxide in the burette and the hydrochloric acid in the conical flask
5. Titrate the contents of the flask againts the NaOH solution and record the titre to the nearest 0.05 cm^3 (when a permanent pink colour appears)
6. Conduct additional titrations until you have concordant values

Question 14

CP3: key points

Answer 14

-rinse the pipette with the HCl solution before measuring out your sample
-calibrate the pipette by ensuring there are no air bubbles in the tip
-rinse and fill the burette with the solution of your tritrant using a funnel

Question 15

CP3: errors

Answer 15

-allow the titrant time to drain down the walls of the burette before reading the volume
-diluting the solutions may produce a reading with a smaller percentage error
-phenolphthalein can turn back to colourless if left to stand because the NaOH reacts with the CO2, in the air to make Na2CO3

Question 16

Core Practical 4: Standard Solutions and Titrations -> experimental objective

Answer 16

-> to make a solution of a known concentration of an acid and use it to find the concentration of a solution of sodium hydroxide

Question 17

CP4: safety

Answer 17

-wear eye protection and suitable chemical resistant gloves
-avoid skin contact with reactants and products
-always use a pipette filler; never use your mouth to suck the liquid up
-take care when clamping and filling the burette that it does not crack or topple over

Question 18

CP4: method

Answer 18

1. Weigh an empty test tube and then add aporixmately 2.5 g sulfamic acid into it
2. Accurately reweigh the test tube and its contents
3. Dissolve the sulfamic acid in 100 cm^3 of distilled water
4. Transfer the solution and washings to a volumetric flask and use distilled water to make it up to the graduation mark
5. Prepare the apparatus for titrations and use a pipette to measure out a 25.0 cm^3 sample of the acid solution into a conical flask with a few drops of methyl orange indicator
6. Titrate the contents of the flask against the NaOH and record the resulsts to the nearest 0.05 cm^3
7. Repeat the titration until you have concordant results

Question 19

CP4: key points

Answer 19

-the acid used must have a high molar mass to reduce weighing errors
-the sample must be pure and impurities can affect the calculated concentration
-the sample must not be air sensitive or react with any air components (e.g. absorbing CO2 or H2O)

Question 20

CP4: errors

Answer 20

-be careful not to lose any solid when transferring from the weighing bottle to the beaker
-when weighing out a solid, wight by difference and then calculate the mass of a solid in a beaker
mass of bottle + beaker - mass of empty bottle

Question 21

Core Practical 5: Hydrolysis of Halogenoalkanes -> experimental objective

Answer 21

-> to investigate the relative rates of hydrolysis of primary, secondary, tertiary halogenoalkanes and of chloro, bromo and iodoalkanes

Question 22

CP5: safety

Answer 22

-wear eye protection and suitable chemical resistant gloved
-avoid skin contact with reactants and products
-there must be no naked flames in the vicnicity as halogenoalkanes and ethanol are flammable
-the laboratory needs to be well ventilated to prevent the inhalation of fumes

Question 23

CP5: method

Answer 23

1. Set up a water bath using a 250 cm^3 beaker with water around 50 ºC
2. Take three test tubes and add 5 cm^3 of ethanol to each one
3. Add four drops of 1-iodobutane to the first test tube, 1-bromobutane to the second test tube and 1-chlorobutane to the third test tube
4. Loosely place bungs in the test tubes and place them in a water bath
5. Take three clean test tubes and pour 5 cm^3 of silver nitrate solution into each one and also place in the water bath
6. When the halogenoalkane-ethanol solutions have reached the temp. of the water bath, add a silver nitrate to each tube and measure the time taken for the precicipitate to form
7. Repeat step 6 using the primary, secondary and tertiary halogenoalkanes

Question 24

CP5: key points

Answer 24

-this is a nucleophilic substitution reaction where water acts as the nucleophile- it is also known as hydrolysis
-the equation for the formation of the precipitation is:
RX + H2O -> ROH + H+ + X-
X- (aq) + Ag+ (aq) -> AgX (s)
-the variables that are independently controlled are the nature of the halide (chloro,bromo or iodo) or the type of alkane (primary, secondary or tertiary)

Question 25

CP5: expected results

Answer 25

-Chloroalkane -> white precipitate forms slowly -Bromoalkane -> cream precipitate forms faster than chloro but slowed than iodo -Iodoalkane -> yellow precipitate forms quickly -this is due to the relative strength of the C-X bond -C-I is the wekest bond so it is the easiest one to break therefore the precipitate forms the quickest -C-CL is the strongest bond so it is the hardest one to break therefore the precipitate forms the slowest

Question 26

CP5: errors

Answer 26

-ensure that the water bath is at the correct temperature to control the temperature of the halogenoalkane -use lower temperatures to reduce the rates of reaction as it makes the time difference between the halogenoalkanes larger, giving a lower uncertainty

Question 27

Core Practical 6: Chlorination of 2-methylpropan-2-ol -> experimental objective

Answer 27

-> to produce and purify a sample of 2-chloro-2-methylpropane

Question 28

CP6: safety

Answer 28

-this procedure requires the use of a working fume cupboard -wear eye protection- goggles are preferred -avoid skin contact with the reactants and products - wear gloves -avoid inhaling vaopurs -the product of the distillation process is flammable -the fumes from the concentrated hydrochloric acid are toxic and corrosive and must not be inhaled, especially by anyone with a respiratory problem

Question 29

CP6: method

Answer 29

1. Pour 10 cm^3 of 2-methylpropane-2-ol and 35 cm^3 of concentrated hydrochloric acid into a large conical flask and swirl 2. Place the bund in the mouth of the flask and swirl again, remove the bund to release the pressure 3. Continue this for approx. 20 minutes until two layers begin to appear 4. Add approx. 6 g of anhydrous calcium chloride and swirl until dissolved- this will ensure all unreacted alcohol goes into the bottom aquous layer and not the top organic layer 5. Transfer the reaction to a separating funnel and allow it to settle into two layers, run off and discard the lower layer but keep the upper layer

Question 30

CP6: method 2.0

Answer 30

6) Add aprox. 10 cm^3 sodium hydrogencarbonate solution to the separating funnel and swirl whilst releasing the pressure, run off and discard the lower aqueous layer and repeat 7. Run off the organic layer into a small conical flask and add a spatula of anhydrous sodium sulfate, swirl and leave until the mixture looks completely clear 8. Decant the organic liquid into a 50 cm^-3 pear-shaped flask and set up for distillation 9. Collect the fraction boiling between 50ºC and 52ºC 10. Analyse the sample by adding 5 cm^3 ethanol and 1 cm^3 sodium hydroxide and warm in a water bath 11. Add excess nitric acid and a few drops of silver nitrate and record the observations

Question 31

CP6: key points and errors

Answer 31

-a weaker base is used to prevent hydrolysis of the halogenoalkane -if sodium hydroxide was used, it could react with the product via nucleophilic substitution -the equation for the reaction is: (CH3)3COH + HCl -> (CH3)3CCl + H2O -be aware that some product may be lost when transferring liquids between the different vessels used

Question 32

Core Practical 7: Oxidation of Porpan-1-ol -> experimental objective

Answer 32

-to oxidise propan-1-ol to produce propanal by heating and distillation -to oxidise propan-1-ol to produce propanoic acid by heating under reflux and distillation

Question 33

CP7: safety

Answer 33

-wear goggles and chemical resistant gloves -propan-1-ol and propanal are flammable -avoid skin contact with reactants and products

Question 34

CP7: method -propanal

Answer 34

1. Add 20 cm^3 acidified potassium dichromate(VI) to a pear-shaped flask and cool using an ice water bath 2. Set the flask for distillation and add some anti-bumping granules (for smoother boiling) 3. Measure 1.5 cm^3 propan-1-ol into a measuring cylinder and add 5 cm^3 distilled water 4. Using a pipette, add the propan-1-ol solution slowing into the pear shaped flask 5. When the propan-1-ol is added, cool the flask to room temperature 6. Light a burner under the flask and gently heat 7. Collect the colourless liquid given off in a test tube that is immersed in cold water

Question 35

CP7: testing for propanal -> Silver Mirror

Answer 35

-Silver Mirror- Tollens Reagant: 1. add 5 drops pf sodium hydroxide solution to 2 cm^3 of silver nitrate solution 2. add just enough ammonia solution to dissolve the precipitate 3. add 10 drops of this to the distillate, if a silver mirror appears it is a positive test

Question 36

CP7: testing for propanal -> Magnesium Ribbon

Answer 36

1. add a small piece of magnesium ribbon to the distillate 2. propanol does not react so ther should be no effervescence

Question 37

CP7: testing for propanal -> Sodium hydrogencarbonate

Answer 37

1. add a spatula of sodium hydrogencarbonate to the distillate 2. propanol does not react so there should be effervescence

Question 38

CP7: testing for propanal -> Fehling's solution

Answer 38

1. add 1 cm^3 Fehling's solution to 1 cm^3 of the distillate and place in hot water 2. if a colour change to red-brown is seen, propanal has been formed

Question 39

CP7: method- propanoic acid

Answer 39

1. Add 20 cm^3 acidified potassium dichromate(VI) to a pear-shaped flask and cool using an ice water bath 2. Set the flask for reflux and add some anti-bumping granules (for smoother boiling) 3. Measure 1.5 cm^3 propan-1-ol into a measuring cylinder and add 5 cm^3 distilled water 4. Using a pipette, add the propan-1-ol soliton slowing into the pear shaped flask 5. When the propan-1-ol is added, cool the flask to room temperature 6. Light a burner under the flask and gently heat under reflux for 30 mins 7. Distil the product using the distillation apparatus, collect the colourless liquid given off in a test tube that is immersed in cold water

Question 40

CP7: testing for propanoic acid -> Silver Mirror

Answer 40

-Silver Mirror- Tollens Reagent 1. add 5 drops of sodium hydroxide solution to 2 cm^3 of silver nitrate solution 2. add just enough ammonia solution to dissolve the precipitate 3. add 10 drops of this to the distillate, if propanoic acid has been made a silver mirror will not appear on the walls of the test tube

Question 41

CP7: testing for propanoic acid -> Magnesium Ribbon

Answer 41

1. add a small piece of magnesium ribbon to the distillate 2. propanoic acid will react with magensium to produce effervescence

Question 42

CP7: testing for propanoic acid -> Sodium hydrogencarbonate

Answer 42

1. add a spatula of sodium hydrogencarbonate to the distillate 2. propanoic acid will react with sodium hydrogencarbonate to produce effervescence

Question 43

CP7: testing for propanoic acid ->Fehling's Solution

Answer 43

1. add 1 cm^3 Fehling's solution to 1 cm^3 of the distillate and place in hot water 2. if no colour change is seen, propanoic acid has been formed

Question 44

CP7: key points

Answer 44

-when oxidising alcohols, it is important to control the conditions as these will dictate the products that are formed -the equation for these reactions is: CH3CH2CH2OH + [O] -> CH3CH2CHO + H2O CH3CH2CHO + [O] -> CH3CH2COOH -carboxylic acids are weak acids however they still react in the same way as other acids such as hydrochloric acid

Question 45

Core Practical 8: Analysis of Unknown Substances -> experimental objective

Answer 45

-> to identify several unknown colourless liquids and inorganic solids

Question 46

CP 8: safety

Answer 46

-wear eye protection -avoid skin contact with reactants and products -ammonia solution gives off ammonia gas which should not be inhaled by anyone, especially those with respiratory problems -ethanol is flammable

Question 47

CP8: Method Chemical Tests

Answer 47

1. Flame test to identify cations 2. Sodium hydroxide test to identify cations 3. Silver nitrate test to identify halide ions 4. Barium nitrate test to identify sulfate ions 5. Hydrochloric acid test to identify sulfate ions 6. Use the results to identify each unknown inorganic substance 7. Bromine water test for alkenes 8. Tollens/Fehling's/Potassium dichromate(VI) for aldehydes 9. Hydrochloric acid or ethanol test for carboxylic acids 10. Use the results to identify each unknown organic substance

Question 48

CP8: results -> inorganic tests -> Flame Tests

Answer 48

-flame tests may be carried out by using a clean nichrome wire to mix a smaple of a solid compound with a few drops of concentrated hydrochloric acid -the wire is then held at the edge of a hot Bunsen flame and the colour observed -yellow -> sodium -lilac -> potassium -yellow-red -> calcium -pale green -> barium -red* -> lithium, strontium -red-violet -> rubidium

Question 49

CP8: results -> Silver Nitrate Solution

Answer 49

-aqeuous nitrate is used for the presence of halide ions in solution -anions such as carbonate that would form precipitates with silver nitrate are removed by adding dilute nitric acid before the silver nitrate -the identity of the halide may be confirmed by adding aquous ammonia to the silver halide -chloride, Cl- -> white, AgCl, soluble (dilute) -bromide, Br- -> cream, AgBr, insoluble (dilute), soluble (concentrated) -iodide, I- -> pale yellow, AgI, insoluble (dilute), insoluble (concentrated)

Question 50

CP8: results -> Bariumd chloride solution

Answer 50

-aqeuous barium chloride forms precipitate with a number of anions but is usually used as the test for the sulfate(VI), SO42- anion -when dilute hydrochloric acid is added to the anion solution before the addition of aqueous barium chloride then only the sylfate(VI) anion will form a precipitate -sulfate(VI), SO42-, white, BaSO4, precipitate is insoluble -sulfate(IV), SO32-, white, BaSO3, precipitate dissolves -carbonate, CO32-, white, BaCO3, precipitate dissolves

Question 51

CP8: results -> Concentrated sulfuric acid

Answer 51

-when a few drops of concentrated sulfuric acid are added to be a solid halide the observed products may be used to identify the halide ion -the test must be carried out on a small scale and in a fume cupboard -the gaseous products in brackets will not be observed since they are colourless -chloride, Cl-, steamy fumes, HCl (products) -bromide, Br-, steamy fumes, brown vapour, Hbry, Br2, (SO2) (products) -iodide, I-, steamy fumes, purple vapour, black solid, yellow solid, HI, I2, S, (H2S) (products)