Analysis and Synthesis

Question 1

Which metals can be identified using flame tests?

Answer 1

Group 1 and 2 metals

Question 2

What colours do different metals turn the flame in a flame test?

Answer 2

• Lithium - Crimson red
• Sodium - Yellow
• Potassium - Lilac
• Calcium - Red
• Barium - Green

Question 3

Which types of metal hydroxides are insoluble in water?

Answer 3

Those of most metals that have ions with 2+ and 3+ charges

Question 4

What happens when sodium hydroxide is added to solutions of metals ions with 2+ and 3+ charges?

Answer 4

A precipitate of the metal hydroxide forms

Question 5

Which metals form white precipitates?

Answer 5

Aluminium, calcium, and magnesium

Question 6

What happens when excess sodium hydroxide solution is added to the precipitate/solution of aluminium hydroxide?

Answer 6

It dissolves

Question 7

State the colours of:

Copper_(II) hydroxide

Iron_(II) hydroxide

Iron_(III) hydroxide

Answer 7

• Copper_(II) hydroxide is blue
• Iron_(II) hydroxide is green
• Iron_(III) hydroxide is brown

Question 8

Why might you test lithium and calcium ions with sodium hydroxide solution as well as a flame test?

Answer 8

They both produce red flames which can be difficult to tell apart from a single test

Calcium ions form a white precipitate when sodium hydroxide is added but lithium does not

Question 9

Write an equation for testing Iron_(III) with sodium hydroxide

Answer 9

Fe³⁺_(aq) + 3OH^- → Fe(OH)_3(s)

This is a balances ionic equation (i.e. don’t include the sodium)

Question 10

What are the three types of negative ions you might test for?

Answer 10

• Carbonate ions
• Halide ions
• Sulfate ions

Question 11

How would you test for carbonate ions?

Answer 11

Add dilute hydrochloric acid to the substance to see if it fizzes

If it does and the substance produced turns limewater milky, the substance contains carbonate ions

This is because a salt, water, and CO₂ are produced

Question 12

How would you test for halide ions?

Answer 12

Add dilute nitric acid and then silver nitrate solution

• Chlorine ions give a white precipitate
• Bromine ions give a cream precipitate
• Iodine ions give a yellow precipitate

AgNO_3(aq) + NaCl_(aq) → AgCl_(s) + NaNO_3(s)

Question 13

How would you test for sulfate ions?

Answer 13

Add dilute hydrochloric acid and then barium chloride solution

If a white precipitate forms, sulfate ions are present

BaCl_2(aq) + MgSO_4(aq) → BaSO_4(s) + MgCl_2(aq)

Question 14

What is a titration?

Answer 14

A method for measuring the volumes of two solutions that react together

Question 15

What is the end-point?

Answer 15

The point at which an acid-base/neutralisation reaction is complete

Question 16

How would you perform a titration?

Answer 16

• Use a pipette to accurately measure the volume of alkali into a conical flask
• Add an indicator to the alkali
• Fill a burette with acid
• Use the burette to gradully add the acid to the alkali. Stop when the idicator changes colour (at the end point)
• Take the burette reading
• Repeat this several times

Question 17

What is concentration measured in?

Answer 17

g/dm³ or mol/dm³

Question 18

How much is 1dm³ in cm³?

Answer 18

1000cm³

1 X 10 X 10 X 10

1dm³ = 1L

Question 20

Why have large databases of the results of analyses been built up? (What are they used for)

Answer 20

• To identify substances in samples
• To identify individuals
• To monitor the cganges in amounts of substances over time

Question 21

What is equilibrium?

Answer 21

The point in a reversible reaction in which the forward and backward rates of reaction are the same

Therefore, the amounts of substances remains constant but not the same

Both reactions continue to occur, but the amounts of products + reactants remains the same

Question 22

What conditions must there be for equilibrium to be achieved?

Answer 22

The reversible reaction must happen in a closed system

This means no products can escape

Question 23

How can the amounts of reactants and products in a reversible reaction be changed?

Answer 23

By changing the reaction conditions

Think of equilibrium as a see-saw, if you take something off one side, the other side will try and make more of it to balance the see-saw!

Question 24

If the forward reaction produces more molecules of gas, what effect does changing the pressure of the reaction have?

Answer 24

An increase in pressure decreases the amount of products formed

A decrease in pressure increases the amount of products formed

Question 25

If the forward reaction produces fewer molecules of gas, what effect does changing the pressure of the reaction have?

Answer 25

An increase in pressure increases the amount of products formed

A decrease in pressure decreases the amount of products formed

Question 26

If the forward reaction is exothermic, what effect with temperature have on the amount of products formed?

Answer 26

An increase in temperature decreases the amount of product formed

A decrease in temperature increases the amount of product formed

Question 27

If the forward reaction is endothermic, what effect with temperature have on the amount of products formed?

Answer 27

An increase in temperature increases the amount of product formed

A decrease in temperature decreases the amount of product formed

Question 28

Which type of reaction does increasing the temperature favour?

Answer 28

Endothermic

Question 29

Which type of reaction does decreasing the temperature favour?

Answer 29

Exothermic

Question 30

What happens if the pressure is increased?

Answer 30

The position of equilibrium will shift to try and reduce the pressure

Question 31

What is the Haber process used to manufacture and what can this be used to make?

Answer 31

Ammonia

This can be used to make fertilisers and other chemicals

Question 32

Describe the Haber process

Answer 32

• Nitrogen from the air and hydrogen (usually from natural gas) are purified and mixed in the correct proportions
• The gases are passed over an iron catalyst at a temperature of 450°C and a pressure of 200 atmospheres
• Some ammonia produced breaks down into nitrogen and hydrogen, so the yield of ammonia is only about 15%
• The gases that come out of the reactor are cooled so the ammonia condenses
• The liquid ammonia is seperated from the unreacted gases. These are then recycled so they are not wasted

Question 33

What is the equation for the Haber process?

Answer 33

N_2(g) + 3H_2(g) ⇌ 2NH_3(g)

Question 34

Why is a pressure of 200 atmospheres used in the Haber process?

Answer 34

• The products have fewer molecules of gas than the reactants, so the higher the pressure the greater the yield of ammonia
• However, the higher the pressure, the more energy is needed to compress the gas.
• Higher pressures also need stronger reaction vessels and pipes which increase costs
• 200 atmospheres is a compromise

Question 35

Why is a temperature of 450°C used in the Haber process?

Answer 35

• The forward reaction is exothermic, so the lower the temperature the greater the yield of ammonia
• However, the reaction rate decreases as the temperature is lowered
• The iron catalyst also becomes ineffective so it would take longer to produce any ammonia
• A compromise temperature of 450°C is used to give a reasonable yield in a short time