12th grade chemical reactions, acids and bases

Question 1

What volume of 2 mol/dm³ stock solution is needed to make 200 cm³ of 0.25 mol/dm³ solution, in cm³?

Answer cm³

Question 2

What is the difference between a strong acid and a weak acid?

• A. A strong acid is always more concentrated
• B. Strong acids are alkalis
• C. A strong acid fully ionises in water; a weak acid only partly ionises
• D. A weak acid has no hydrogen

Question 3

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

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

Question 4

Why is acid added dropwise near the end point?

• A. to keep the burette full
• B. to make the indicator brighter
• C. to avoid adding too much past the end point
• D. because drops react faster

Question 5

Solution X has pH 4 and solution Y has pH 5. How many times greater is the hydrogen ion concentration in X than in Y?

Answer 

Question 6

20 cm³ of a solution is diluted 5 times (its concentration becomes 1/5 of the original). How much water must be added, in cm³?

Answer cm³

Question 7

2H₂ + O₂ → 2H₂O. 1 mol of hydrogen reacts with 6 mol of oxygen. What is the maximum amount of water that can form, in mol? Give 2 decimal places if needed.

Answer mol

Question 8

25 cm³ of 0.2 mol/dm³ sodium hydroxide is neutralised by 20 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 9

Zinc is added to a solution containing iron ions and displaces the iron. Which species is oxidised?

• A. zinc atoms
• B. iron ions

Question 10

20 cm³ of 1 mol/dm³ acid is diluted with water to a total volume of 40 cm³. What is the new concentration, in mol/dm³?

Answer mol/dm³

Question 11

A compound has the empirical formula CH₂ (mass of one unit = 14) and Mr = 56. How many empirical units are in one molecule?

Answer 

Question 12

Mg + 2HCl → MgCl₂ + H₂. 3 mol of magnesium is mixed with 5 mol of hydrochloric acid. Which is the limiting reactant?

• A. magnesium
• B. hydrochloric acid

Question 13

Magnesium ribbon is added to acid until bubbling stops and some magnesium is left. Which reactant was limiting?

• A. neither
• B. the magnesium
• C. the hydrogen
• D. the acid

Question 14

A strong acid solution has a hydrogen ion concentration of 0.001 mol/dm³. What is its pH? (pH = −log₁₀[H⁺])

Answer 

Question 15

Titres (cm³): rough 25, run 1 24.25, run 2 24.3. Ignoring the rough titre, calculate the mean titre from the concordant results (within 0.10 cm³), in cm³. Give 2 decimal places.

Answer cm³