chemistry required practicals paper 1

Question 1

What is the aim of the soluble salts practical?

Answer 1

-To prepare a pure, dry sample of a soluble salt from an acid and an insoluble base.

Question 2

What type of reaction is used to make soluble salts?

Answer 2

-A neutralisation reaction between an acid and an insoluble base.

Question 3

-Which acid and base are commonly used to make copper sulfate?

Answer 3

-Sulfuric acid and copper oxide.

Question 4

: What is the first step in making soluble salts?

Answer 4

Warm the acid gently using a Bunsen burner – do not boil it.

Question 5

Why do we warm the acid?

Answer 5

• To speed up the reaction with the copper oxide.

Question 6

What is added to the warm acid and why?

Answer 6

-Add the copper oxide until no more dissolves – this ensures all the acid reacts.

Question 7

What is done after excess base is added?

Answer 7

• The mixture is filtered to remove the excess unreacted base.

Question 8

What happens to the filtrate?

Answer 8

-It is the salt solution – this is transferred to an evaporating basin.

Question 9

How do you obtain pure, dry crystals of the salt?

Answer 9

• Gently heat the filtrate to evaporate some water, then leave it to cool and crystallise.

Question 10

Why must the solution be left to crystallise slowly?

Answer 10

-: Slow crystallisation forms larger, purer crystals.

Question 11

How is the final salt dried?

Answer 11

-Crystals are collected and gently dried with filter paper or in a warm place.

Question 12

Give an example of a salt made in this required practical.

Answer 12

• Copper sulfate (CuSO₄) made from copper oxide and sulfuric acid.

Question 13

how do you make soluble salts - required practical

Answer 13

-Gently heat the sulfuric acid using a Bunsen burner – do not boil.
-Add the copper oxide in small amounts and stir.
-Continue adding the copper oxide until no more dissolves – this means all the acid has reacted.
-Filter the mixture to remove excess, unreacted copper oxide
-Gently heat the solution in an evaporating basin to evaporate some water.
-Leave the solution to cool and crystallise, then dry the crystals with filter paper or in a warm place.

Question 14

What is the purpose of a titration?

Answer 14

-To find out exactly how much acid is needed to neutralise a known volume of alkali

Question 15

What type of reaction is a titration based on?

Answer 15

-Neutralisation - acid reacts with alkali to form a salt and water.

Question 16

What piece of equipment is used to measure the acid accurately?

Answer 16

-A burette.

Question 17

What piece of equipment is used to measure a fixed volume of alkali?

Answer 17

-A pipette.

Question 18

What is used to transfer the alkali into the conical flask?

Answer 18

-A pipette and pipette filler.

Question 19

Why is a conical flask used instead of a beaker?

Answer 19

• To reduce splashing when swirling during the titration.

Question 20

How do you fill the burette with acid safely?

Answer 20

• Using a funnel at eye level, and make sure the jet space is filled.

Question 21

What should you do to get precise results in titrations?

Answer 21

• Repeat until you have at least two concordant results (within 0.10 cm³).

Question 22

how do you carry out a titration

Answer 22

-Use a pipette and pipette filler to measure 25 cm³ of alkali into a conical flask.
-Add a few drops of methyl orange indicator to the alkali in the conical flask.
-Fill a burette with acid, making sure the jet space is filled and the burette is clamped vertically.
-Do a rough titration to estimate the endpoint by adding acid while swirling until the indicator changes colour.
-Repeat the titration slowly and accurately, recording the volume when the colour change happens (the endpoint).
-Repeat until you get two concordant results (within 0.10 cm³) and calculate the mean titre.

Question 23

-What is the aim of the temperature changes required practical?

Answer 23

• To investigate the temperature change during an exothermic reaction between a metal and an acid

Question 24

Why is a polystyrene cup used instead of a beaker?

Answer 24

• It acts as an insulator, reducing heat loss to the surroundings.

Question 25

What is the role of the lid in the practical?

Answer 25

-To reduce heat loss and evaporation from the cup.

Question 26

How can you make the practical more reliable?

Answer 26

- Repeat the experiment and calculate a mean temperature change.

Question 27

What safety precautions should be taken?

Answer 27

-: Wear goggles, handle acids with care, and use a lid to avoid splashes.

Question 28

: What does a rising temperature indicate about the reaction?

Answer 28

-It’s an exothermic reaction – heat is being released.

Question 29

What does a falling temperature indicate about the reaction?

Answer 29

- It’s an endothermic reaction – heat is being absorbed.

Question 30

Describe how you would investigate the temperature change of a reaction using the temperature changes required practical.

Answer 30

-Place a polystyrene cup in a beaker for support and insulation. -Add 25 cm³ of HCl to the cup using a measuring cylinder. -Record the starting temperature using a thermometer. -Add the magnesium and stir the mixture. -Record the maximum (or minimum) temperature reached after the reaction. -Repeat the experiment and calculate the mean temperature change for accuracy.

Question 31

What is electrolysis?

Answer 31

-The process of breaking down an ionic compound using electricity.

Question 32

What type of electrodes are used and why?

Answer 32

- Inert carbon electrodes, because they don’t react with the electrolyte.

Question 33

What happens at the cathode during electrolysis?

Answer 33

Reduction – positive ions gain electrons (e.g. Cu²⁺ → Cu).

Question 34

What happens at the anode during electrolysis?

Answer 34

-: What is the half equation for copper at the cathode?

Question 35

What is the half equation for copper at the cathode?

Answer 35

-Cu²⁺ + 2e⁻ → Cu

Question 36

What is the half equation for chloride at the anode?

Answer 36

- 2Cl⁻ → Cl₂ + 2e⁻

Question 37

What observations are made during electrolysis of copper(II) chloride?

Answer 37

-Brown copper forms at the cathode, and bubbles of chlorine gas at the anode.

Question 38

How can you test for chlorine gas?

Answer 38

-It bleaches damp blue litmus paper white.

Question 39

Why must the electrodes not touch each other?

Answer 39

- It would short-circuit the cell and stop electrolysis.

Question 40

What safety precautions should be taken during electrolysis?

Answer 40

: Wear goggles, use a fume cupboard (if available) for chlorine gas, and wash hands after handling solutions.

Question 41

Describe how to carry out the electrolysis required practical using copper(II) chloride solution.

Answer 41

-Pour copper(II) chloride solution into a beaker to act as the electrolyte. -Insert two carbon electrodes into the solution and make sure they do not touch each other. -Connect the electrodes to a low-voltage power supply using crocodile clips and wires. -Switch on the power supply – copper forms at the cathode (brown solid). -Chlorine gas forms at the anode, seen as bubbles; test it with damp blue litmus paper (it turns white). -Record the observations at each electrode and write half equations for the reactions.