past paper questions recent

Question 1

explain what is meant by a saturated solution

Answer 1

• a solution where the maximum amount of solute has been dissolved
  -at a particular temperature

Question 2

state one property of metals

Answer 2

-high melting points
-good conductors of electricity

Question 3

state one observation made during the combustion of magnesium metal

Answer 3

bright white flame

Question 4

state one chemical property of the product of combustion that can be used to classify magnesium as a material

Answer 4

magnesium oxide is a base

Question 5

explain why magnesium sulfide has a very high melting point

Answer 5

1) strong electrostatic forces of attraction
2) between magnesium and sulfide ions
3) therefore lots of energy is required to overcome these forces

Question 6

at the end of the experiment there is no zinc left in the flask

give a conclusion the student could make from this observation

Answer 6

The acid was in excess

Question 7

the student did not make any mistakes in their measurements

explain what could’ve caused the studen’ts value for x to be too low

Answer 7

1) not all of the water had evaporated
2) not heated for long enough

Question 8

describe how the student could improve the method to obtain a more accurate value for x

Answer 8

repeat until constant mass

Question 9

state what is meant by the term covalent bond

Answer 9

an attraction between a shared pair of electrons and both atoms nuclei.

Question 10

a student compares the reactivity of elements bromine, chlorine and iodine.

He mixes these pairs of solutions and observes the reactions that occur

• chlorine solution and potassium bromide solution
• bromine solution and potassium iodide solution

explain how the reactions can be used to show the order of reactivity of the 3 elements

Answer 10

chlorine solution and potassium bromide solution:
1) solution turns orange
2) because chlorine displaces bromine
3) so chlorine is more reactive than bromine

bromine solution and potassium iodide solution:
1) solution turns brown
2) because bromine displaces iodine
3) so bromine is more reactive than iodine

Question 11

explain why it is neccessary to add excess zinc

Answer 11

• to make sure all of the zinc and acid react
• so that a pure zinc sulfate solution is obtained

Question 12

explain two changes that the student should make to his method to obtain a mass of magnesium oxide closer to the expected mass

Answer 12

1) take of the lid to allow air to enter the crucible
2) reheat to constant mass to make sure all the magnesium has reacted

Question 13

explain why the student needs to stir the mixture

Answer 13

1) to keep the same temp throughout the experiment
2) more reactant particles come into contact with eachother

Question 14

describe how the student could identify which solid is pure and which is a mixture by measuring a physical property of each solid

Answer 14

1) test using the melting point
2) if these solids melt at a fixed point
3) if melts over a range of temps, the substance is a mixture

Question 15

state another method of preventing iron from rusting

Answer 15

sacrificial protection

Question 16

explain which substance is the oxidising agent

Answer 16

the substance that loses oxygen

Question 17

identify the ion that makes the sodium hydroxide solution alkaline

Answer 17

hydroxide / OH-

Question 18

suggest a reason why the results might not be as accurate at temperatures higher than 60 degrees

Answer 18

1) the solution would not remain at required temp

Question 19

suggest another reason why the student stirs the solution

Answer 19

to ensure temp same throughout solution

Question 20

give a reason why the crucible and contents are heated for a further 3 minutes

Answer 20

1) to obtain a constant mass
2) to show reaction is complete

Question 21

other than spillages, suggest a possible reason why the student’s yield is less than expected

Answer 21

1) sodium hydrogencarbonate was impure
2) not all sodium hydrogencarbonate reacted

Question 22

describe how the student could obtain a pure dry sample of lead(11) nitrate crystals

Answer 22

1) heat acid in a water bath
2) add the lead oxide to the dilute nitric acid
3) filter off excess solid
4) heat solution gently, using a bunsen burner to evaporate off some of the water
5) leave then solution to cool and allow the salt to crystallise
6) filter off solid salt and leave it to dry

Question 24

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