Question

You need to quickly make a solution of solid potassium chloride in water. Explain what you would do to minimize the time it would take and why each step works.

Answer 1

Potassium chloride is available as solid powder and is highly soluble in water. Potassium chloride doesn’t absorb water significantly or lose in mass considerably; hence, can be easily weighed on an analytical balance. Solid potassium chloride available from suppliers is usually greater than 95% pure and for all practical purposes, we will consider the powder to be pure and start our preparations by weighing out the powder.

Suppose you wish to prepare 100 mL of 5% (m/v) potassium chloride solution. This means every 100 mL water will contain 5 g potassium chloride (we assume that the volume change due to addition of potassium chloride is negligible). Simply weigh out 5 g potassium chloride on an analytical balance (correct to three or four decimal places); pour the powder in a 100 mL or 150 mL beaker and add water, swirl to dissolve the powder and finally make up the volume to the 100 mL mark with water. This shall give you the desired 5% potassium chloride solution.