12th grade chemical reactions, acids and bases

Question 1

10 cm³ of 0.5 mol/dm³ acid is diluted with water to a total volume of 100 cm³. What is the new concentration, in mol/dm³?

Answer mol/dm³

Question 2

A strong acid solution has a hydrogen ion concentration of 1 × 10⁻⁶ mol/dm³. What is its pH? (pH = −log₁₀[H⁺])

Answer 

Question 3

Which piece of equipment measures exactly 25.0 cm³ of alkali into the flask?

• A. a measuring cylinder
• B. a test tube
• C. a volumetric pipette
• D. a beaker

Question 4

What volume of 1 mol/dm³ stock solution is needed to make 200 cm³ of 0.25 mol/dm³ solution, in cm³?

Answer cm³

Question 5

2H₂ + O₂ → 2H₂O. 1 mol of hydrogen is mixed with 1 mol of oxygen. Which is the limiting reactant?

• A. hydrogen
• B. oxygen

Question 6

20 cm³ of 0.1 mol/dm³ sodium hydroxide is neutralised by 12.5 cm³ of sulfuric acid. H₂SO₄ + 2NaOH → Na₂SO₄ + 2H₂O. What is the concentration of the acid, in mol/dm³? Give 3 decimal places.

Answer mol/dm³

Question 7

A strong acid is diluted so its H⁺ concentration becomes 10 times smaller. What happens to its pH?

• A. it rises by 1
• B. it falls by 1
• C. it rises by 10
• D. it does not change

Question 8

Titres (cm³): rough 24.23, run 1 23.18, run 2 23.08. Ignoring the rough titre, calculate the mean titre from the concordant results (within 0.10 cm³), in cm³. Give 2 decimal places.

Answer cm³

Question 9

2Na + Cl₂ → 2NaCl. 1 mol of sodium reacts with 2 mol of chlorine. What is the maximum amount of sodium chloride that can form, in mol? Give 2 decimal places if needed.

Answer mol

Question 10

Solution X has pH 3 and solution Y has pH 4. How many times greater is the hydrogen ion concentration in X than in Y?

Answer 

Question 11

Complete the half-equation at the cathode: Fe³⁺ + ? e⁻ → Fe. How many electrons are needed?

Answer 

Question 12

Find the empirical formula: a compound is 40 % carbon, 6.7 % hydrogen and 53.3 % oxygen (Ar: C = 12, H = 1, O = 16).

• A. CH₂O
• B. CHO
• C. C₂H₄O
• D. C₆H₁₂O₆

Question 13

In a car engine with too little air, which reactant is limiting and what is the risk?

• A. fuel is limiting, so too much oxygen forms
• B. oxygen is limiting, so incomplete combustion makes carbon monoxide
• C. nitrogen is limiting, so no reaction happens
• D. nothing is limiting

Question 14

A compound has the empirical formula CH (mass of one unit = 13) and Mr = 78. How many empirical units are in one molecule?

Answer 

Question 15

Redox: which statement is NOT true?

• A. Oxidation and reduction always happen together.
• B. A metal atom becoming a positive ion is reduced.
• C. Oxidation is the loss of electrons.
• D. Reduction is the gain of electrons.