) Explain the purpose of washing the sand with hot water. Why was it important to wash the sand with hot water? How would the experimental results be affected by washing the sand with cold water instead of hot water?
Depends on what you are trying to do, but it is most likely to ensure you are washing away all the salts that you can.
Some salts are more soluble at higher temperatures, so by washing the sand with hot water, you are ensuring that you can wash away as much of the salt as possible. That is one guess.