12th grade chemical reactions, acids and bases

Question 1

Iron is added to a solution containing copper ions and displaces the copper. Which species is reduced?

• A. iron atoms
• B. copper ions

Question 2

What volume of 1 mol/dm³ stock solution is needed to make 500 cm³ of 0.5 mol/dm³ solution, in cm³?

Answer cm³

Question 3

Complete the half-equation at the cathode: Al³⁺ + ? e⁻ → Al. How many electrons are needed?

Answer 

Question 4

Solution X has pH 5 and solution Y has pH 6. How many times greater is the hydrogen ion concentration in X than in Y?

Answer 

Question 5

N₂ + 3H₂ → 2NH₃. 5 mol of nitrogen reacts with 4 mol of hydrogen. What is the maximum amount of ammonia that can form, in mol? Give 2 decimal places if needed.

Answer mol

Question 6

Why is one reactant often used in excess in industry?

• A. To make sure all of the more expensive reactant reacts
• B. To slow the reaction down
• C. To make the product impure on purpose
• D. Because excess reactants are free

Question 7

2H₂ + O₂ → 2H₂O. 4 mol of hydrogen is mixed with 8 mol of oxygen. Which is the limiting reactant?

• A. hydrogen
• B. oxygen

Question 8

Ocean water's pH has fallen from about 8.2 to about 8.1 since the 1800s. Roughly how has the H⁺ concentration changed?

• A. it has not changed
• B. it has increased by about 25–30 %
• C. it has fallen by half
• D. it has increased 10 times

Question 9

25 cm³ of a solution is diluted 10 times (its concentration becomes 1/10 of the original). How much water must be added, in cm³?

Answer cm³

Question 10

Find the empirical formula: a hydrocarbon is 80 % carbon and 20 % hydrogen by mass (Ar: C = 12, H = 1).

• A. C₄H
• B. C₂H₆
• C. CH₄
• D. CH₃

Question 11

Redox: which statement is NOT true?

• A. Oxidation and reduction always happen together.
• B. Oxidation is the loss of electrons.
• C. In a displacement reaction, the more reactive metal is oxidised.
• D. Reduction always means gaining oxygen.

Question 12

A strong acid solution has a hydrogen ion concentration of 1 × 10⁻³ mol/dm³. What is its pH? (pH = −log₁₀[H⁺])

Answer 

Question 13

A compound has the empirical formula C₂H₅ (mass of one unit = 29) and Mr = 58. How many empirical units are in one molecule?

Answer 

Question 14

Why is the conical flask swirled during a titration?

• A. to change the indicator
• B. to speed up evaporation
• C. to mix the solutions so the end point is seen accurately
• D. to cool the flask

Question 15

Titres (cm³): rough 23.24, run 1 22.49, run 2 22.39. Ignoring the rough titre, calculate the mean titre from the concordant results (within 0.10 cm³), in cm³. Give 2 decimal places.

Answer cm³