Why does sand heated in a test tube and water mixed together create heat?

Question

I had a lab where we heated sand in a testube on an alcohol burner and after it cooled we put water in it and it became hot. Why does this happen? What's in the sand that causes it?

I touched it and it was cool enough to hold the test tube in my hand.

It also turned red

Answer 1

There is only one way to heat water. Energy must be added to it. This can happen in several ways. For example:
1. Heat transfer from bunsen burner, hot sand or hot test tube.
2. An exothermic chemical reaction in the water
3. Radiation of the water (e.g., a lamp)
4. Agitation of the water (stirring or shaking vigorously)
5. A substance disolves in the water (this can cause an increase or decrease in temperature depending on the 'heat of solution' of the substance)

Ask yourself these questions:
1. Where all sources of heat differential removed to avoid heat transfer? (i.e., was the sand truly the same temperature as the water?)
2. Was there a chemical in the sand that caused an exothermic chemical reaction in the water?
3. Were there sources of radiation acting on the test tube?
4. Did you mix the water and sand vigorously?
5. Was there a substance in the sand that has a high heat of solution? (table salt (NaCl)would have a negative heat of solution, but LiCl has a high positive heat of solution)

Answer 2

What do you mean "after it cooled"? How do you know it cooled? I'm guessing that it hasn't cooled completely. When you put the water in it, the heat left in the sand heats up the water.

Answer 3

I haven't the foggiest