Final answer:
To add more powdered mix to water, heating up the water is key as it increases solubility, unlike stirring, which only affects the rate of dissolution but not the total amount that can be dissolved.
Step-by-step explanation:
To add more powdered mix to water, heating up the water first is effective because it increases the solubility of the powdered mix. This is due to the fact that, for many substances, solubility does increase with temperature. An example of this is how sugar dissolves more rapidly in hot water compared to cold. When water is heated, the kinetic energy of its molecules increases, allowing greater interaction between the water and the solute, which facilitates dissolving.
However, if the solution is already saturated, as seen when adding more solid magnesium hydroxide, there is no increase in the concentration of dissolved ions as the added compound remains undissolved. Stirring the solution can accelerate the rate of dissolution but won't increase the overall amount of solute that can be dissolved. Thus, for a solution that is not yet saturated, heating the water will effectively allow more powdered mix to dissolve.