Practicals

Question 1

Describe the method of making up a standard volumetric solution for an acid-base titration

Answer 1

1. Calculate the mass of required substance needed to produce
   250 cm3

of a 0.100 mol dm-3 solution.
2. Weigh a clean dry weighing bottle (or weighing boat) on a 2dp
balance.

3. Place the weighing bottle on the pan of a digital balance and
   zero the balance. Using a spatula, place (approximately) the
   calculated mass of required substance into the bottle.
4. Remove from the balance, set to zero and re-weigh the weighing
   bottle and its contents, recording the value.
5. Pour the contents of the weighing bottle into a clean, glass
   beaker and re-weigh the weighing bottle, recording the value
6. Calculate the mass of required substance that you have
   transferred to the beaker [difference in two mass values].
7. Add approximately 100 cm3
   of deionised (or distilled) water to
   the beaker containing the solid. Use a glass rod to stir the
   contents of the beaker until all the solid has dissolved.
8. Using a funnel, pour the contents of the beaker into a 250 cm3
   volumetric flask. Using further deionised (or distilled) water in a
   wash bottle, wash out the beaker and funnel, transfering all
   washings into the volumetric flask.
9. Make the volumetric flask up to the graduated mark by carefully
   adding deionised water from a wash bottle.
10. Stopper the volumetric flask and invert to combine thoroughly (shake)

Question 2

How would you do a titration?

Answer 2

1. Pour approximately 100cm3
   of the standard
   solution of known concentration into a beaker.
2. Fill the burette with the standard solution of
   known concentration.
3. Pour approximately 100cm3
   of the solution with
   unknown concentration into a second beaker.
4. Using a pipette filler and pipette to transfer
   exactly 25cm3
   of solution into a 250cm3
   conical
   flask.
5. Add two to three drops of phenolphthalein
   indicator to the solution in the conical flask and
   note the initial colour of the indicator.
6. Record the initial burette reading (bottom of meniscus)
7. Titrate the contents of the conical flask by
   adding solution to it from the burette until the
   indicator undergoes a definite, permanent
   colour change. Record the final burette reading
   in your table of results. Calculate the titre
   volume (change in volume in the burette).
8. Repeat, calculate and record the volume of
   solution used in the titration in a table (titre
   volume). Repeat until two concordant results
   are obtained. Record all of the results that you obtain.

Question 3

Describe the method of ‘measuring and enthalpy change’

Answer 3

For: anhydrous copper sulfate + aq&raquo_space;> copper sulfate solution

1. Weigh out anhydrous copper sulfate (e.g. 4g)
2. Make a time against temperature table with minute intervals, up to 15
3. Use a measuring cylinder to measure out 25cm3 of deionised water
4. Pour this water into a polystyrene cup
5. Record waters initial temperature
6. Stir continuously and record temp every minute
7. at the 4th min, add anhydrous copper sulphate and continue to stir (don’t record temp at this point)
8. Record temp every min from 5-15, still sitring
9. weigh out a sample of hydrated copper sulfate and repeat steps 2-8
   ( add 24cm3 not 25cm3 of water)

Question 4

What are 6 considerations of the calorimetry (Enthalpy change) practical?

Answer 4

1. Weigh in stoppered bottles:
   if exposed to air for a while, may absorb water form atmosphere.
2. Wear gloves:
   anhydrous copper sulfate is an irritant
3. Carry out reaction in a polystyrene cup:
   thermal insulator, prevents heat escaping
4. Dissolve hydrated in less water than anhydrous:
   as hydrated already contains some water
5. Stir contents continuously:
   so temp reading is accurate
6. Dispose of safely:
   Copper sulfate is toxic to aquatic life, should not go down the sink

Question 5

Describe the method of temperature effects rate

Answer 5

1. Add hot and cold water to plastic container (one with 2 holes and an X), so that temp is around 25 degrees
2. Add 10cm3 of hydrochloric acid to a test tube and place this in the hole without the cross underneath
3. Add 10cm3 of sodium thiosulfate solution to a test tube, place this on ein the hole with a cross underneath, and add a thermometer and wait until temp is stable
4. Use a pipette to get 1cm3 of HCl and add to sodium thiosulfate test tube, immediately start a stopwatch
5. Look over tube from above, when solution becomes so cloudy that you can no longer see the cross, stop stopwatch and record time, and note down final temp
6. Dispose of this safely by pouring into a beaker of sodium carbonate solution
7. Repeat at 35, 45, 55, and room temp (15)

Question 6

What are some considerations of the temp effecting rate practical?

Answer 6

1. Cannot perform reaction above 55 degrees:
   will increase rate of SO2 gas to possibly dangerous levels
2. Disposing of reaction mixture in sodium carbonate solution:
   neutralises HCl to stop reaction, no production of SO2 gas
3. Looking at mixture from above tst tube:
   to ensure we look from the same angle each time, as angle can obscure view of cross.

Question 7

Describe the method for inorganic ions practical: group 2 cations with dilute sodium hydroxide

Answer 7

1. add 10 drops of 0.1 mol dm3 magnesium chloride to a test tube
2. Add 10 drops of 0.6 mol dm3 sodium hydroxide to this solution
3. Continue adding sodium hydroxide solution, dropwise with gentle shaking, until in excess (test tube should not be more than half full)
4. When done, dispose contents by putting test tube in a bowl of cold water
5. Repeat with calcium bromide, barium chloride, and strontium chloride.

Question 8

What would you observe with the group 2 cations and dilute sodium hydroxide?

Answer 8

Barium chloride:
Initial- colourless
10 drops- colourless
Excess- colourless

Calcium Bromide:
Initial- colourless
10 drops- slight white ppt
Excess- slight white ppt

Magnesium chloride:
Initial- colourless
10 drops- slight white ppt
Excess- white ppt

Strontium Chloride:
Initial: colourless
10 drops- slight white ppt
Excess- slight white ppt

Question 9

Describe the method of group 2 cations with dilute sulphuric acid

Answer 9

1. 10 drops of 01. mol dm3 barium chloride in a clean test tube
2. Add 10 drops of 1.0 mol dm3, mix well
3. Continue adding dropwise and gentle shaking until in excess (not more than half full)
4. Dispose in water
5. Repeat with calcium bromide, magnesium chloride, and strontium chloride

Question 10

what would you observe with the group 2 cations and dilute sulphuric acid?

Answer 10

Barium chloride:
10 drops- white ppt
Excess- white ppt

Calcium bromide:
10 drops- slight white ppt
Excess- slight white ppt

Magnesium chloride:
10 drops- slight white ppt
Excess- colourless

Strontium chloride:
10 drops- white ppt
Excess- white ppt

Question 11

Explain the method for testing for ammonium ions

Answer 11

1. 10 drops of ammonium chloride into test tube
2. Add 10 drops of sodium hydroxide and shake
3. Warm mixture gently using a water bath
4. Test fumes using forceps to hold a piece of damp red litmus paper in mouth of test tube
5. Dispose by placing test tube in boiling water

Question 12

What should we observe in the testing for ammonium ions practical?

Answer 12

Damp red litmus paper should turn blue

As ammonium ions are basic

Question 13

Explain the method for testing for hydroxide ions in aqueous solution

Answer 13

Test 1cm3 of 0.4 mol dm3 sodium hydroxide in a test tube with red litmus paper .

Will turn damp red litmus paper blue

Question 14

Explain the method for testing for hydroxide ions: ammonia
(hydroxide ions form when it comes into contact with water)

Answer 14

1. Take 5 drops of 1 mol dm3 ammonia solution and place on a filter paper and place inside a petri dish with lid
2. Dampen red litmus paper with distilled water and place on the other side of the petri dish.
3. replace lid and observe over a few minutes
4. ammonia solution vapours will turn damp red litmus paper blue.

Question 15

Describe the method of testing for carbonates in aqueous solution

Answer 15

1. Add an equal, small vol of dilute HCl to sodium carbonate in a test tube.
2. Use a delivery tube to transfer the gas produced into a second test tube containing a small vol of calcium hydroxide (limewater).
3. Put a stopper into the test tube containing the calcium hydroxide solution, shake slightly.
4. The limewater will go cloudy if carbonate ions are present.

Question 16

Describe the test for sulfate ions in aqueous solution

Answer 16

1. 1cm3 of 0.1 mol dm3 magnesium sulphate in a test tube, add equal vol of dilute HCl and equal vol of 0.1 mol dm3 barium chloride.

White ppt

Question 17

What should we do when working with barium chloride?

Answer 17

It is very harmful so wear gloves and a lab coat

Question 18

Describe the method of testing for halide ions in aqueous solution

Answer 18

1. Add a small volume of dilute nitric acid to the solution of potassium chloride
2. Add 2cm of silver nitrate to the solution
3. Swirl tubes to ensure ppts formed are even distributed then divide the contents of each tube in half
4. To one half of the contents add an excess of dilute aqueous ammonia solution and observe
5. To the other half, working in a fume cupboard, add excess of conc ammonia and observe.
6. Repeat with solutions of potassium bromide, and potassium iodide.

Question 19

What are the observations of the halides in aqueous solution?

Answer 19

Potassium Chloride:
silver nitrate - white ppt
dilute ammonia- colourless
conc ammonia- colourless

Potassium Bromide:
silver nitrate- cream ppt
dilute ammonia- cream ppt
conc ammonia- colourless

Potassium Iodide:
silver nitrate- yellow ppt
dilute ammonia- yellow ppt
conc ammonia- yellow ppt

Question 20

describe the method for testing halide ions in solid salts using conc sulphuric acid

Answer 20

1. Place a small spatula measure of solid potassium chloride in a test tube.
2. Working in a fume cupboard, add a few drops of conc sulphuric acid, and record what happens
3. Test any gas evolved with moist blue litmus
4. Repeat with solid potassium bromide and potassium iodide

Question 21

What are the observations for halide ion salts with conc sulphuric acid?

Answer 21

Potassium chloride:
Conc sulphuric- white, steamy fumes
Blue litmus- turns red

Potassium bromide:
Conc sulphuric- orange fumes
Blue litmus- turns red

Potassium iodide:
Conc sulphuric- purple fumes and purple solid
Blue litmus- turns red

Question 22

Describe the method of the distillation practical

Answer 22

1.

Question 23

Describe the test for alcohol using a metal

Answer 23

1. Add a small piece of metallic sodium to alcohol
2. Produces hydrogen gas which is shown by a squeaky pop test
3. Dispose of excess sodium safely using beaker of ethanol

Question 24

Describe the test for alcohol using potassium dichromate

Answer 24

1. Add acidified potassium dichromate
2. Primary and secondary will be reduced from orange to green

Question 25

Describe the test for an aldehyde

Answer 25

1. In a test tube mix equal vol of Fehling's solution A and Fehling's solution B, should be clear dark blue. 2. Add 5 drops of this to a test tube along with some anti-bumping granules, then add aldehyde 3. Warm gently for 2 min in water beaker 4. Brick-red ppt will form if aldehyde is present

Question 26

Describe the test for an alkene

Answer 26

1. Add 1cm3 of bromine water to 2 drops of alkene 2. Shake vigorously from side to side 3. Bromine water decolorises from orange to colourless is alkene is present.

Question 27

Describe the test for a carboxylic acid

Answer 27

1. Place a spatula of solid sodium carbonate in a test tube and add about 2cm3 of dilute ethanoic acid using a pipette. 2. Collect gas produced and bubble through limewater, turns cloudy if carboxylic acid is present as CO2 is produced

Question 28

Explain how you test for a halogenoalkane

Answer 28

1. Using a teat pipette add 5 drops of 1-bromobutane to 1cm3 of sodium hydroxide solution. 2. Warm contents in a beaker of water of 60 degrees 3. Acidify contents by adding 2cm3 of dilute nitric acid and add 1cm3 of silver nitrate solution Silver bromide ppt forms

Question 29

Explain the method of the 'iodine clock' (initial rate)

Answer 29

1. Rinse burette with potassium iodide then fill burette with 50cm3 of potassium iodide 2. Transfer 10cm3 of hydrogen peroxide solution from a burette to a 100cm3 beaker 3. Use a 50cm3 measuring cylinder to add 25cm3 of sulphuric acid to a 250cm3 video 4. use 25cm3 measuring cylinder to add 20cm3 of distilled water into 250cm3 beaker 5. use plastic dropping pipette to add 1cm3 of starch solution to the beaker 6. Use burette to add 5cm3 of potassium iodide solution to the mixture in the 250cm3 beaker. 7. Add 5cm3 of sodium thiosulfate solution from a burette into 250cm3 beaker. 8. Stir this mixture and pour the hydrogen peroxide solution from 100cm3 beaker into 250cm3 beaker and immediately start timer 9. Stop timer when mixture turn blue/black. 10. Rinse beaker with deionised water and dry 11. Repeat all but change conc of potassium iodide 12. Plot graph of initial rate against conc to determine order

Question 30

Continuous monitoring method

Question 31

Describe the method for the EMF of an electrical cell: zinc and copper

Answer 31

1. Clean a piece of copper and zinc using emery paper or sandpaper. 2. Degrease the metal pieces using cotton wool and propanone. 3. Place copper into a 100cm3 beaker with about 1 mol dm3 CuSO4 solution. 4. Place zinc into 100cm3 beaker with about 50cm3 of 1 mol dm3 ZnSO4 solution. 5. Lightly plug one end of a plastic U-tube with cotton wool and fill the tube with solution of 2 mol dm3 sodium chloride solution, plug the other end. 6. Join the two beakers with the U-tube 7. Connect half cells with crocodile clips on the metal and leads, include a voltmeter.

Question 32

Describe the method of comparing electrode potentials of different metals

Answer 32

1. clean piece of copper using emery paper 2. Connect positive terminal of voltmeter using a crocodile clip and one of the leads 3. Cut a piece of filter paper to about the same area as the copper and moisten with sodium chloride solution and place it on top of the metal 4. Connect a second lead to the voltmeter and use the crocodile clip to a different piece of metal 5. Hold metal against filter paper and record voltage 6. Repeat with different metals