What happens to substances during a chemical change

What metric units would you use to measure the thickness of a key

Asample of hydrated tin (ii) chloride (sncl2) has a mass of 4.90 g. when it is dehydrated, it has a mass of 4.10 g. which is the correct chemical formula for the hydrate? sncl2•2h2o          sncl2•4h2o          sncl2•6h2o

Which of the following would not diffuse through the plasma membrane by means of simple diffusion? 1 oxygen 2 glucose 3 a steroid hormone 4 a lipid soluble vitamin