4(a) Copper carbonate reacts with dilute nitric acid - Edexcel - GCSE Chemistry: Combined Science - Question 4 - 2021 - Paper 1

The pH change from 2 to 6 signifies an increase in alkalinity. The relationship between pH and hydrogen ion concentration is given by:

$[H^+] = 10^{-pH}$

Calculating the concentrations:

• At pH 2: $[H^+] = 10^{-2} = 0.01 ext{ M}$
• At pH 6: $[H^+] = 10^{-6} = 0.000001 ext{ M}$

The factor of change in concentration is:

rac{0.01}{0.000001} = 10000

Thus, the answer is D × 1/10000.

To obtain copper sulfate crystals from the copper sulfate solution, follow these steps:

1. Evaporate the Water: Gently heat the copper sulfate solution to evaporate some of the water, concentrating the solution. Be careful not to overheat as it may decompose the copper sulfate.

2. Cool the Solution: Allow the concentrated solution to cool down slowly. As it cools, copper sulfate crystals will begin to form.

3. Collect the Crystals: Once sufficient crystals have formed, filter the solution to separate the crystals from the remaining liquid.

4. Dry the Crystals: Rinse the crystals with a small amount of cold distilled water to remove impurities, then allow them to dry in a warm place.