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Year 7 foundation: C1.13 Chemical formulae and balancing
37 questions · 202 marks, in lesson order.
Chemical reactions
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A student says fizzing proves that a chemical reaction has happened.
What does fizzing show?
(2)Evaluate the claim. Suggest stronger evidence.
(2)Total for this question: 4 marks
Chemical reactions
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A teacher heated a mixture of yellow sulphur and grey iron filings on a metal tray in a fume cupboard. The mixture glowed very brightly. She turned off the Bunsen burner and the glow spread through the mixture. When it cooled, a black solid called iron sulphide was left.
From this information, give one way you can tell that a chemical reaction took place.
(1)What type of substance is each chemical?
(2)Raj held a magnet near each chemical. Iron sulphide was not magnetic. Was each of the other chemicals magnetic?
(1)Name the solid formed when zinc is heated with sulphur.
(1)When fuels containing sulphur burn, the sulphur reacts with oxygen. Complete the word equation.
(1)sulphur + oxygen →
Total for this question: 6 marks
Word equations
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Construct the word equation for the reaction.
(3)sulfuric acid + → +
Identify the gas produced.
(1)Total for this question: 4 marks
Burning fuels
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A carbon-fuel heater is used in a room with poor ventilation.
Explain what happens to the combustion of the fuel.
(3)Explain why carbon monoxide is dangerous.
(2)Total for this question: 5 marks
Burning fuels
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The table gives information about three fuels that can be used in cars. A tick shows that a substance is produced when the fuel burns; a cross shows it is not.
| fuel | physical state | energy released / kJ per kg | carbon monoxide | sulphur dioxide | water |
|---|---|---|---|---|---|
| petrol | liquid | 48 000 | ✓ | ✓ | ✓ |
| hydrogen | gas | 121 000 | ✗ | ✗ | ✓ |
| ethanol (alcohol) | liquid | 30 000 | ✓ | ✗ | ✓ |
Which fuel releases the least energy per kilogram?
(1)Some scientists say that burning hydrogen as a fuel causes less pollution. Use the table to give one reason why.
(1)Which of the three fuels can be compressed into a small container?
(1)Which gas in the air is needed for fuels to burn?
(1)Petrol is made from oil, which could run out in 100 years. Ethanol can be made from sugar cane. Explain why sugar cane will not run out.
(1)Total for this question: 5 marks
Burning fuels
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George burned methanol under a funnel. Air was drawn from the funnel through a U-tube surrounded by ice cubes, then through limewater. Two different gases were produced as the methanol burned.
One of the gases condensed in the cold U-tube to give a colourless liquid. Name this liquid.
(1)The other gas turned the limewater cloudy. Name this gas.
(1)Methanol is used in antifreeze. The label on the bottle shows two hazard symbols: flammable and toxic. Which two precautions should you take when using this antifreeze? Tick both.
(1)Water freezes at 0 °C. The label shows that 10% antifreeze lowers the freezing point to –6 °C, 20% to –12 °C and 30% to –21 °C. Terry used 10% antifreeze in his car’s wash-bottle. One night the temperature fell to –14 °C and the wash-bottle burst. Explain why.
(2)Total for this question: 5 marks
Burning fuels
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Burning fossil fuels causes air pollution.
Give the names of two fossil fuels.
(1)and
Some fossil fuels contain sulphur. Complete the word equation.
(1)sulphur + oxygen →
Acid rain has collected in a lake. A helicopter drops calcium hydroxide into the lake; it dissolves to form an alkaline solution. What effect does the alkali have on the pH of the lake?
(1)Calcium hydroxide reacts with sulphuric acid in the lake. Which salt is formed?
(1)Trees damaged by acid rain lose their leaves and die. Explain why leaves are needed for a tree to grow.
(1)What effect does acid rain have on buildings made from limestone?
(1)Total for this question: 6 marks
Burning fuels
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The shuttle is a spacecraft used to take satellites into space. It has a separate fuel tank containing liquid hydrogen and liquid oxygen.
Explain why hydrogen and oxygen are carried as liquids rather than as gases.
(1)Oxygen is needed to burn the fuel. Vehicles on Earth do not need an oxygen tank. Why does the shuttle need one?
(1)The graph shows the upward force and the total weight of the shuttle and fuel for the first 20 seconds after the fuel is lit. Why does the total weight decrease?
(1)Use the graph. At 20 seconds, give the upward force and the total weight.
(1)upward force millions of N total weight millions of N
At 20 seconds, what is the resultant force on the shuttle?
(1)Use the graph to explain why the shuttle cannot take off before 10 seconds.
(1)Total for this question: 6 marks
Thermal decomposition
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Copper carbonate is heated in an open test tube. The mass of the tube and its contents goes down.
Name the type of reaction and the two products.
(3)Explain why the mass goes down, even though mass is conserved.
(2)Total for this question: 5 marks
Thermal decomposition
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Pure limestone is calcium carbonate. When calcium carbonate is heated above 825 °C it produces calcium oxide and carbon dioxide.
Complete the symbol equation for this reaction.
(2)CaCO₃ → +
Some gases that pollute the air dissolve in rainwater to form acids, which damage limestone statues. Name a gas that dissolves in rainwater, leading to sulphuric acid.
(1)Complete the word equation for the reaction between calcium carbonate and sulphuric acid.
(2)calcium carbonate + sulphuric acid → + + water
Total for this question: 5 marks
Thermal decomposition
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A fire extinguisher contains sodium hydrogencarbonate, NaHCO₃. When heated, it breaks down to carbon dioxide, water and a compound with the formula Na₂CO₃.
Complete the word equation.
(1)sodium hydrogencarbonate → (Na₂CO₃) + carbon dioxide + water
When 168 g of sodium hydrogencarbonate breaks down completely, it produces 44 g of carbon dioxide and 106 g of Na₂CO₃. What mass of water is produced?
(1)How much carbon dioxide is produced when 336 g of sodium hydrogencarbonate breaks down completely?
(1)To put out a fire you can keep oxygen away, take the heat away, or take the fuel away. Carbon dioxide has a density of about 1.8 g per 1000 cm³; air has about 1.2 g per 1000 cm³. Explain why carbon dioxide is used to put out fires.
(2)Water from another extinguisher evaporates when sprayed on a fire. Why does evaporation cool the fire down?
(1)Total for this question: 6 marks
Conservation of mass
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A reaction that makes a gas is done twice: in an open flask the mass goes down, but in a sealed flask it stays the same.
Explain why the mass goes down in the open flask.
(3)Explain why the mass stays the same in the sealed flask.
(2)Total for this question: 5 marks
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