What is the mas of 1.2(23)molecules of ammonia NH3

If 90.0 grams of ethane reacted with excess chlorine,how many grams of dicarbon hexachloride would form

Suppose that some of the compound spilled out of the crucible after it was heated. would that cause the percent by mass of water in the compound determined by the experiment to be too low, too high, or unchanged? briefly explain your answer.

If a particle has z = 25 and 23 electrons, what is its charge?