Question
Nitrogen dioxide, NO2, is an atmospheric pollutant and is formed in car engines.
(a) Explain how nitrogen dioxide is formed in car engines. [2]
(b) Nitrogen dioxide causes respiratory problems.
State one other adverse effect of nitrogen dioxide.[1]
(c) Nitrogen dioxide emissions can be reduced by adding an aqueous solution of urea, (NH2)2CO, to car exhaust gases.
The heat of the exhaust gases breaks down the urea into simpler substances.
(i) Name the type of reaction which occurs when a substance is heated and breaks down into simpler substances.[1]
(ii) One molecule of urea breaks down to form one molecule of ammonia and one other molecule.
Complete the chemical equation to show the formula of the other molecule formed in this reaction.
(NH2)2CO → NH3 + [1]
(iii) State the test for ammonia.[2]
test
observations
(d) The ammonia formed reacts with nitrogen dioxide to form nitrogen and water.
(i) Balance the equation for this reaction.
NO2 + NH3 → N2 + 12H2O [2]
(ii) State how the equation shows that the nitrogen in nitrogen dioxide is reduced.[1]
(iii) This reaction is a redox reaction.
State the meaning of the term redox.[1]
(e) 135 moles of urea, (NH2)2CO, is stored in the tank of a car.
Calculate the mass, in kg, of the stored (NH2)2CO.
mass of (NH2)2CO = kg [2]
(f) Another oxide of nitrogen formed in car engines is nitrogen monoxide, NO. A catalytic converter removes NO by reacting it with a gas formed by incomplete combustion of the fuel. Two non‑toxic gases are formed.
(i) Name the gas formed by incomplete combustion of the fuel.[1]
(ii) Name the two non‑toxic gases formed. and [1] [Total: 15]
Answer/Explanation
Ans:
3(a) nitrogen (from air) and oxygen (from air) react
react due to high temperatures (of engine)
3(b) acid rain
3(c)(i) (thermal) decomposition
3(c)(ii) HCNO
3(c)(iii) (damp red) litmus
(litmus) turns blue
3(d)(i) 6NO2 8NH3 7N2
either 6NO2 or 8NH3
all three balanced
3(d)(ii) (nitrogen) loses oxygen
3(d)(iii) reduction and oxidation occur
3(e) Mr urea = 60
135 × 60 = 8100 and g to kg conversion = 8.1(00) kg
3(f)(i) carbon monoxide
3(f)(ii) carbon dioxide and nitrogen
Question
A student adds excess large pieces of magnesium carbonate, MgCO3, to dilute hydrochloric acid, HCl, and measures the volume of carbon dioxide gas, CO2, given off.
(a) Add the missing state symbols to the chemical equation for the reaction.
MgCO3 ….. + 2HCl….. → MgCl 2(aq) + H2O ….. + CO2 ….. [1]
(b) Complete the dot-and-cross diagram to show the electron arrangement of the ions in magnesium chloride.
The inner shells have been drawn.
Give the charges on the ions.[3]
(c) Complete the dot-and-cross diagram to show the electron arrangement in a molecule of carbon dioxide.
Show outer shell electrons only.[2]
(d) The graph shows how the volume of carbon dioxide gas changes with time.
(i) Describe how the graph shows that the rate of this reaction decreases as time increases.[1]
(ii) Explain, in terms of particles, why the rate of this reaction decreases as time increases.[2]
(iii) The student repeats the experiment using powdered MgCO3 instead of large pieces.
All other conditions stay the same.
On the grid, draw the line expected when powdered MgCO3 is used instead of large pieces. [2]
(e) Determine the volume of CO2 gas given off when excess MgCO3 is added to 25.0cm3 of 0.400mol/dm3 HCl at room temperature and pressure.
MgCO3 + 2HCl → MgCl2 + H2O + CO2
Use the following steps.
- Calculate the number of moles of HCl in 25.0cm3 of 0.400mol/dm3 of acid.
mol
- Determine the number of moles of CO2 gas given off.
mol
- Calculate the volume of CO2 gas given off in cm3.
cm3 [3] [Total: 14]
Answer/Explanation
Ans:
2(a) MgCO3(s) + 2HCl(aq) → MgCl2(q) + H2O(l) + CO2(g)
2(b) eight crosses in second shell of Mg
7 dots and 1 cross in third shell of both Cl
2+ charge on Mg and – charge on both Cl ions on correct answer line
2(c) C atom double bonded to 2 O atoms
4 non-bonding e– on each O and no non-bonding e– on C and both octets complete
2(d)(i) gradient (of line) decreases
2(d)(ii) concentration of particles (of acid) decreases
lower rate of collisions of particles
2(d)(iii) a new line steeper than printed line and starts at origin and levels off earlier than printed line
levels off at the same volume
2(e) M1 mol HCl = 0.400 × 25.0 / 1000 = 0.01(00)
M2 mol CO2 = M1 / 2 = 0.0100 / 2 = 0.005(00)
M3 volume CO2 = M2 × 24000 = 120 (cm3)
Question
This question is about salts.
(a) Salts that are insoluble in water are made by precipitation.
● Lead(II) iodide, \(PbI_2\), is insoluble in water.
● All nitrates are soluble in water.
● All sodium salts are soluble in water.
You are provided with solid lead(II) nitrate, \(Pb(NO_3)_2\), and solid sodium iodide, NaI.
Describe how you would make a pure sample of lead(II) iodide by precipitation.
Your answer should include:
● practical details
● a chemical equation for the precipitation reaction.
(b) Nitrates decompose when heated.
(i) When hydrated zinc nitrate is heated, oxygen gas is given off.
Describe a test for oxygen.
test ……………………………………………………………………………………………………………………..
observations ………………………………………………………………………………………………………..
(ii) Complete the equation for the decomposition of hydrated zinc nitrate.
\(2Zn(NO_3)_2•6H_2O → …..ZnO + …..NO_2 + O_2 + …..H_2O\)
(c) Some sulfates are hydrated.
When hydrated sodium sulfate crystals, Na2SO4•xH2O, are heated, they give off water.
\(Na_2SO_4•xH_2O(s) → Na_2SO_4(s) + xH_2O(g)\)
A student carries out an experiment to determine the value of x in \(Na_2SO_4•xH_2O\).
step 1 Hydrated sodium sulfate crystals are weighed.
step 2 The hydrated sodium sulfate crystals are then heated.
step 3 The remaining solid is weighed.
(i) Describe how the student can check that all the water has been given off.
(ii) In an experiment, 1.61g of \(Na_2SO_4•xH_2O\) is heated until all the water is given off. The mass of \(Na_2SO_4\) remaining is 0.71g.
\([M_r : Na_2SO_4,142; H_2O,18]\)
Determine the value of x using the following steps.
● Calculate the number of moles of \(Na_2SO_4\) remaining.
………………………… mol
● Calculate the mass of \(H_2O\) given off.
………………………… g
● Calculate the number of moles of \(H_2O\) given off.
………………………… mol
● Determine the value of x.
x = …………………………
Answer/Explanation
Answer:
(a) (add) water (to both salts) (1)
dissolve both salts / make solutions (1)
filter (lead(II) iodide)(1)
wash (residue of lead(II) iodide) with water AND dry e.g. with filter paper / description of washing and drying (1)
\(Pb(NO_3)_2 + 2 NaI → 2NaNO_3 + PbI_2\)
OR \(Pb^{2+} + 2I^– → PbI_2\) (1)
(b) (i) glowing splint (1)
relights / rekindles (1)
(ii) 2ZnO(s) and \(4NO_2\)(g) (1)
\(12H_2O\)(g) (1)
(c) (i) heat again and weigh again / repeat steps 2 and 3 (1)
until mass is constant (1)
(ii) 0.005 (1)
0.9 (1)
(0.9 ÷ 18 =) 0.05 (1)
(0.05 ÷ 0.005 =) 10 (1)