Question: what is the percent composition of water in magnesium sulfate heptahydrate?
Answer: A typical analysis of kieserite reveals 15.0% magnesium (25% as magnesium oxide, 75% as magnesium sulfate), 20.0% sulfur (as sulphate), up to 2.5% chlorides, and 12% water. When not stored in closed containers, specimens of kieserite will absorb water from the air and be converted to magnesium sulfate heptahydrate.