10th grade chemical reactions, acids and bases

Question 1

Marble chips and acid were placed on a balance. The mass fell from 135.5 g to 133.1 g in 200 s as carbon dioxide escaped. What was the mean rate of reaction, in g/s? Give 3 decimal places.

Answer g/s

Question 2

Cracking: C₁₂H₂₆ → C₆H₁₄ + an alkene. How many hydrogen atoms are in one molecule of the alkene?

Answer 

Question 3

On a reaction profile, the reactants are at 120 kJ, the peak is at 310 kJ and the products are at 210 kJ. What is the overall energy change, in kJ? (Use a minus sign if energy is released.)

Answer kJ

Question 4

Reactants: 60 kJ. Peak of the profile: 145 kJ. Products: 95 kJ. What is the activation energy, in kJ?

Answer kJ

Question 5

Why is extracting aluminium by electrolysis so expensive?

• A. The electrodes are made of gold
• B. It needs huge amounts of electricity to melt the ore and drive the reaction
• C. Aluminium is less reactive than carbon
• D. Aluminium ore is very rare

Question 6

Extracting metals: which statement is NOT true?

• A. Carbon can reduce zinc oxide to zinc.
• B. Gold is found uncombined because it is very unreactive.
• C. An ore is a rock containing enough metal to make extraction worthwhile.
• D. Aluminium can be extracted by heating its oxide with carbon.

Question 7

Why is recycling aluminium cans so worthwhile?

• A. Aluminium cannot be extracted from ore
• B. It uses about 5 % of the energy needed to extract new aluminium
• C. Recycling makes aluminium heavier
• D. New aluminium is radioactive

Question 8

Volume of gas collected: 0 s: 0 cm³; 20 s: 27 cm³; 40 s: 42 cm³; 60 s: 50 cm³; 80 s: 55 cm³; 100 s: 57 cm³. What was the mean rate between 60 s and 80 s, in cm³/s? Give 2 decimal places.

Answer cm³/s

Question 9

8 g of copper sulfate is dissolved in water to make 200 cm³ of solution. What is the concentration, in g/dm³? (1 dm³ = 1000 cm³)

Answer g/dm³

Question 10

12.5 g of sodium hydroxide is dissolved to make 2.5 dm³ of solution. What is the concentration, in g/dm³?

Answer g/dm³

Question 11

How is platinum usually obtained?

• A. electrolysis
• B. reduction with carbon
• C. found as the native metal

Question 12

What mass of glucose is needed to make 500 cm³ of solution with a concentration of 15 g/dm³, in g?

Answer g

Question 13

Alkenes and cracking: which statement is NOT true?

• A. Alkenes contain a carbon–carbon double bond.
• B. Ethene can be used to make the polymer poly(ethene).
• C. Alkanes decolourise bromine water.
• D. Cracking is a thermal decomposition reaction.

Question 14

How does a catalyst change a reaction profile?

• A. It removes the reactants
• B. It lowers the peak (activation energy) but not the overall energy change
• C. It changes an exothermic reaction into an endothermic one
• D. It raises the products

Question 15

Electrolysis of sodium sulfate solution: what forms at the cathode (negative electrode)?

• A. zinc
• B. hydrogen
• C. sodium
• D. aluminium

Question 16

Why does a closed system matter for equilibrium?

• A. It keeps the system warm
• B. It adds a catalyst
• C. Nothing can enter or leave, so both reactions can balance
• D. It makes the reaction irreversible