1 (a) The concentration of a solution can be calculated using the equation concentration of solution = \frac{mass \ of \ solid}{volume \ of \ solution} A student dissolved 9.25g of ammonium chloride in water and made up the solution to a volume of 200 cm³ - Edexcel - GCSE Chemistry Combined Science - Question 1 - 2021 - Paper 1

The process of dissolving ammonium chloride in water is endothermic because:

1. The ammonium chloride solution (product) has more energy than the ammonium chloride solid and the water (reactants).
2. Additionally, during the dissolution, the energy of the system increases and the energy change is positive.
3. Consequently, heat energy has been absorbed during the process.

The reaction profile should show the progress of the dissolution process with energy on the y-axis and the reaction coordinate on the x-axis. The activation energy needs to be labeled, which is the energy difference between the reactants and the peak of the profile.

From Figure 3, the investigation shows that:

1. Solid ammonium chloride did not light up the lamp, indicating that electricity did not pass through it.
2. However, the ammonium chloride solution lit up brightly, suggesting that the solution allowed current to flow, which implies it conducts electricity due to the presence of ions in solution.