Sodium Hydroxide in Water

sodium hydroxide ions in solution

When sodium hydroxide is dissolved in water it feels warm, which indicates an exothermic reaction.
NaOH (s) → Na+ (aq) + OH- (aq)

M&M Color Wheel

M&Ms in water, candy coating dissolving

When M&M’s are placed in water, the outer shell, which is made of sugar, dissolves. The sugar moves from a place of high concentration (the M&M) to a place of low concentration (the water away from the M&M). When the sugar shell dissolves and moves outward, it takes the layer of food dye with it. When more than one M&M is placed into a petri dish the colors do not mix because the concentration of sugar at the interface is approximately the same. Also, around the bottom of the M&M water appears cloudy because the sugar that is dissolved is more dense than the water, so it sinks.

Ammonium Nitrate in Water

ammonium nitrate ions in solution

When ammonium nitrate is dissolved in water it feels cold, which indicates an endothermic reaction.
NH4NO3 (s) → NH4+ (aq) + NO3- (aq)