C3 - Analysis & Synthesis

Question 1

What are the two main methods for testing for positive ions?

Answer 1

• Flame test

- Reaction with sodium hydroxide.

Question 2

How is a flame test carried out?

Answer 2

• The compound is put on a cleaned wire loop
• The loop is then held in a Bunsen burner.
• The colour of the flame can be used to identify a positive ion.

Question 3

What colour flame does lithium produce?

Answer 3

Crimson

Question 4

What colour flame does sodium produce?

Answer 4

Yellow

Question 5

What colour flame does potassium produce?

Answer 5

Lilac

Question 6

What colour flame does calcium produce?

Answer 6

Red

Question 7

What colour flame does barium produce?

Answer 7

Green

Question 8

What possible elements are present if a white precipitate forms in sodium hydroxide?

Answer 8

Al3+, Ca2+, Mg2+

Question 9

How is it possible to distinguish between Al, Ca and Mg ions?

Answer 9

• Adding more NaOH causes aluminium ions to dissolve.

- Calcium can be identified with a flame test.

Question 10

Which ions produce a blue precipitate with NaOH?

Answer 10

Copper(II)

Question 11

Which ions produce a green precipitate with NaOH?

Answer 11

Iron(II)

Question 12

Which ions produce a brown precipitate with NaOH?

Answer 12

Iron(III)

Question 13

How can negative carbonate ions be identified?

Answer 13

• Adding dilute acid produces CO2 gas.

- Limewater is then turned cloudy.

Question 14

How can negative halide ions be identified?

Answer 14

• Nitric acid then silver nitrate solution is added.

- If a precipitate forms, halides are present.

Question 15

Which ions produce a white precipitate with silver nitrate?

Answer 15

Chloride

Question 16

Which ions produce a cream precipitate with silver nitrate?

Answer 16

Bromide

Question 17

Which ions produce a yellow precipitate with silver nitrate?

Answer 17

Iodide

Question 18

How can negative sulfate ions be identified?

Answer 18

• Hydrochloric acid then barium chloride is added.

- If a white precipitate forms, sulfate ions are present.

Question 19

What is titration used for?

Answer 19

To measure how much acid and alkali react completely.

Question 20

What is the end-point of a reaction?

Answer 20

The point at which the acid and alkali have reacted completely.

Question 21

What is a pipette used for?

Answer 21

Measure out a fixed solution.

Question 22

What is a burette used for?

Answer 22

Measuring the volume added.

Question 23

How is the concentration of a solution calculated?

Answer 23

• Calculate the mass in 1cm3 of solution.
• Calculate mass of solute in 1000cm3 of solution.
• Convert the mass to moles.

Question 24

How is the mass of solute calculated?

Answer 24

• Calculate the mass of the solute in 1dm3.
• Calculate mass in 1cm3.
• Calculate the mass in the given volume.

Question 25

What technique is used to analyse DNA?

Answer 25

Gel electrophoresis

Question 26

Give two examples of chemical analysis in medicine.

Answer 26

- DNA can be matched to find suitable donors. | - Metal concentrations can be analysed to indicate joint failures.

Question 27

What is the point of equilibrium?

Answer 27

When the rate of forward and reverse reactions are equal.

Question 28

What happens when a system of equilibrium is changed?

Answer 28

When a system of equilibrium is subjected to a change then the position of equilibrium will shift to oppose the change.

Question 29

How does changing the pressure affect reversible reactions involving gases?

Answer 29

- Increasing the pressure favours the reaction with the least number of molecules of gas formed. - Decreasing the pressure favours the reaction with the greater number of molecules of gas formed.

Question 30

How does changing the temperature affect reversible reactions?

Answer 30

- Increasing the temperature favours the endothermic reaction. - Decreasing the temperature favours the exothermic reaction.

Question 31

If the forward reaction of a reversible reaction is exothermic, what must the reverse reaction be?

Answer 31

Endothermic

Question 32

Give five examples for the uses of ammonia.

Answer 32

- Dye - Fibre making - Nitric acid - Fertiliser - Explosives

Question 33

What makes the Haber process so efficient?

Answer 33

- Unreacted hydrogen and oxygen are reused. | - Steam is used to turn generators.

Question 34

How is the nitrogen for the Haber process obtained?

Answer 34

Hydrogen is burned with air to give nitrogen and water.

Question 35

How is the ammonia gas collected?

Answer 35

It is condensed into a tank.

Question 36

How can the yield of ammonia be changed?

Answer 36

Increasing the pressure.

Question 37

Why does an increase in pressure increase the yield of ammonia?

Answer 37

There are four molecules going in and two going out meaning the pressure favours the forward reaction.

Question 38

What pressure is the Haber process undertaken at?

Answer 38

200atm

Question 39

Why is the Haber process done at the given pressure?

Answer 39

It gives a high yield at a lesser expense.

Question 40

What temperature is the Haber process carried out at?

Answer 40

200C

Question 41

Why can't the Haber process be carried out at a lower temperature?

Answer 41

The rate of reaction would be too slow.

Question 42

Why can't the Haber process be carried out at a higher temperature?

Answer 42

- The forward reaction is exothermic. | - A lower temperature favours the forward reaction.

Question 43

What is used as a catalyst in the Haber process?

Answer 43

Iron

Question 44

What does the presence of a catalyst do in the Haber process?

Answer 44

- Doesn't increase yield. | - Forms ammonia faster.

Question 45

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Answer 45

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