I have used this lab for 3 years as an introduction to molarity. Using kool-aid is not only fun, but it gives the students some grounding to fall back on to when we start talking about actual molarity problems.
This activity drives home the idea of concentration but towards the end of the lab, it ties together with molarity itself. It allows students to make their own connections and develop what molarity means and how it is used in their everyday lives.
Kool-Aid powder (the type with sugar included)
Straws (I cut these in half for mini-stirring straws)