(a) Sulfur dioxide is a pollutant in the air.
(i) State one source of sulfur dioxide in the air
(ii) Sulfur dioxide is oxidised to sulfur trioxide in the air.
Oxides of nitrogen act as catalysts for this reaction.
What is meant by the term catalyst?
(iii) Sulfur trioxide dissolves in rainwater to form acid rain.
Which one of the following pH values could be the pH of acid rain?
Draw a circle around the correct answer.[1]
pH 4 pH 7 pH 9 pH 13
(iv) State one adverse effect of acid rain on buildings.
(b) Sulfur dioxide melts at –73 °C and boils at –10 °C.
What is the physical state of sulfur dioxide at –20 °C?
Explain your answer
(c) Excess sulfuric acid reacts with ammonia to make a salt which can be used as a fertiliser.
State the name of the salt formed when excess sulfuric acid reacts with ammonia
(d) The table shows some observations about the reactivity of four metals with dilute sulfuric acid.
Use the information in the table to put the four metals in order of their reactivity. Put the least reactive metal first.
▶️ Answer/Explanation
(a)(i) Burning fossil fuels (coal/oil) or volcanic eruptions are primary sources of sulfur dioxide emissions.
(a)(ii) A catalyst is a substance that increases the rate of a chemical reaction without being consumed in the process.
(a)(iii) pH 4 (acid rain is weakly acidic, with pH typically between 4-5).
(a)(iv) Acid rain reacts with calcium carbonate in limestone/marble buildings, causing erosion and deterioration.
(b) Liquid state. At -20°C (between melting point -73°C and boiling point -10°C), sulfur dioxide exists as a liquid.
(c) Ammonium sulfate – formed when 2 moles of ammonia react with 1 mole of sulfuric acid.
(d) Tungsten < nickel < iron < magnesium. Reactivity increases as we observe more vigorous reactions (from no reaction to slow/fast fizzing).
The table shows the masses of some of the ions in 1000 cm3 of fruit juice.
(a) Answer these questions using only the information in the table.
(i) State which negative ion has the highest mass in 1000 cm3 of fruit juice.
(ii) Give the formulae of the ions in ammonium sulfate.
(iii) Calculate the mass of sodium ions in 200 cm3 of fruit juice.
mass = ………………………… mg
(b) Describe a test for lithium ions.
(c) Ions of the element potassium, K, are present in most fertilisers.
State the names of two other elements that are in most fertilisers.
(d) Orange juice is acidic.
Draw a circle around the pH of orange juice.
pH 4 pH 7 pH 10 pH 13
(e) Some soils are acidic.
Give the names of two compounds that are used to make soils less acidic.
(f) Hydrogen chloride is an acidic gas produced when concentrated hydrochloric acid evaporates.
(i) Describe the arrangement and separation of the molecules in hydrogen chloride gas.
(ii) A long glass tube is set up as shown.
At first, the blue litmus paper does not turn red.
After a short time, the litmus paper turns red.
Explain these observations using the kinetic particle model.
▶️ Answer/Explanation
(a)(i) Ans: Cl– (chloride)
The table shows chloride has the highest mass (142 mg) among negative ions.
(a)(ii) Ans: NH4+ and SO42-
Ammonium sulfate (NH4)2SO4 contains ammonium (NH4+) and sulfate (SO42-) ions.
(a)(iii) Ans: 24 mg
Calculation: (120 mg ÷ 1000 cm3) × 200 cm3 = 24 mg
(b) Ans: Flame test (1), red flame observed (1)
Lithium ions produce a characteristic crimson-red flame in the flame test.
(c) Ans: Nitrogen (1) and Phosphorus (1)
Most fertilizers contain NPK – Nitrogen (N), Phosphorus (P), and Potassium (K).
(d) Ans: pH 4 circled
Orange juice is weakly acidic with a typical pH around 3.5-4.5.
(e) Ans: Any two from: calcium carbonate (1), calcium oxide (1), calcium hydroxide (1)
These alkaline compounds neutralize soil acidity by reacting with H+ ions.
(f)(i) Ans: Random arrangement (1), far apart (1)
Gas molecules have no fixed arrangement and are widely spaced compared to liquids/solids.
(f)(ii) Ans: Key points (any 3 for full marks):
• HCl molecules evaporate and diffuse through the tube (1)
• Molecules move randomly in all directions (1)
• Movement causes gradual spread from high to low concentration (1)
• When HCl reaches litmus, it dissolves and forms acidic solution (1)