Astudent is investigating the affect of different salts on melting points. four patches of ice of equal size are roped off and a different type of salt is poured on each, one receives table salt (nacl), one receives calcium chloride (cacl2), one receives potassium carbonate (kco3) and the fourth receives inert sand instead. each patch receives an equal amount of salt or sand. the student measures the volume of ice remaining and subtracts it from the original volume of ice to see how much melted away. what is a control variable in this experiment?

Astudent is given a sample of a blue copper sulfate hydrate. he weighs the sample in a dry covered porcelain crucible and got a mass of 23.875 g for the crucible, lid, and sample. the mass of the empty crucible and lid was found earlier to be 22.652 g. he then heats the crucible to expel the water of hydration, keeping the crucible at red heat for 10 minutes with the lid slightly ajar. on colling, he finds the mass of crucible, lid, and contents to be 23.403 g. the sample was changed in the process to very light clue anhydrous cuso4. if there are again 100.0 g of hydrate, how many grams of cuso4 are in it? how many moles of cuso4? (hint: molar mass of cuso4 = 159.6 g / mole. what per cent of the hydrate is cuso4? you may convert the mass of cuso4 to moles.)