10th grade chemical reactions, acids and bases

Example

Electrolysis of copper(II) chloride solution: what forms at the cathode (negative electrode)?

1. Solution: compare the metal with hydrogen in the reactivity series.
2. So the answer is: copper

Answer: copper

Example

On a reaction profile, the reactants are at 80 kJ, the peak is at 220 kJ and the products are at 140 kJ. What is the overall energy change, in kJ? (Use a minus sign if energy is released.)

1. 140 − 80 = 60
2. Positive: energy is taken in (endothermic).
3. So the answer is: 60 kJ

Answer: 60 kJ

Example

Magnesium reacted with acid and 24 cm³ of hydrogen was collected in 20 s. What was the mean rate of reaction, in cm³/s?

1. 24 ÷ 20 = 1.2
2. So the answer is: 1.2 cm³/s

Answer: 1.2 cm³/s

Example

All substances are gases in this equilibrium: N₂O₄ ⇌ 2NO₂. The forward reaction is endothermic. The pressure is increased. What happens to the position of equilibrium?

1. Higher pressure favours the side with fewer gas molecules.
2. So the answer is: shifts left (more reactants)

Answer: shifts left (more reactants)

Example

Cracking: C₁₁H₂₄ → C₅H₁₂ + an alkene. How many hydrogen atoms are in one molecule of the alkene?

1. C: 11 − 5 = 6
2. H: 24 − 12 = 12
3. The alkene is C₆H₁₂.
4. So the answer is: 12

Answer: 12

Example

How is iron usually obtained?

1. Metals less reactive than carbon can be extracted by heating their oxides with carbon.
2. So the answer is: reduction with carbon

Answer: reduction with carbon

Example

10 g of sodium hydroxide is dissolved to make 0.5 dm³ of solution. What is the concentration, in g/dm³?

1. 10 ÷ 0.5 = 20
2. So the answer is: 20 g/dm³

Answer: 20 g/dm³