Question: how many molecules in 5 grams of water?
Answer: Water consists of two hydrogen atoms connected to one oxygen atom, therefore molecular mass of water (M) is equal to sum of molecular masses of oxygen and two hydrogen atoms which is 2x1. 01 +15.99. Therefore molecular mass of water (M) is equal to 18,01. So in 5g sample of water there is 1.67 x 1023 water molecules.