9th grade chemical reactions, acids and bases

Example

Balance the equation. What number goes in the gap? __Al + 3Cl₂ → 2AlCl₃

1. 2Al + 3Cl₂ → 2AlCl₃
2. Al: 2 on the left, 2 on the right.
3. So the answer is: 2

Answer: 2

Example

A reaction produces 150 cm³ of gas in 50 seconds. What is the mean rate of reaction, in cm³/s?

1. 150 ÷ 50 = 3
2. So the answer is: 3 cm³/s

Answer: 3 cm³/s

Example

Reactivity series (most reactive first): potassium, sodium, calcium, magnesium, aluminium (aluminum), zinc, iron, copper, silver, gold. If calcium is added to a solution of iron sulfate, will a displacement reaction happen?

1. calcium is more reactive than iron, so it displaces it.
2. So the answer is: yes

Answer: yes

Example

Which gas gives this result: bubbled through limewater, it turns it milky?

1. Carbon dioxide turns limewater milky (cloudy).
2. So the answer is: carbon dioxide

Answer: carbon dioxide

Example

A flame test gives a lilac flame. Which metal ion is present?

1. Potassium compounds give a lilac flame.
2. So the answer is: potassium, K⁺

Answer: potassium, K⁺

Example

Alkanes have the general formula CₙH₂ₙ₊₂. How many hydrogen atoms are in an alkane with 11 carbon atoms?

1. 2 × 11 + 2 = 24
2. So the answer is: 24

Answer: 24