Final answer:
Besides water loss due to heating, the change in mass on heating MgSO₄ 7H₂O crystals could be due to a chemical reaction where MgSO4 may react with oxygen to form lighter compounds. Escape of gaseous products in an open system might also lead to mass decrease.
Step-by-step explanation:
Other than water loss from heating MgSO₄ 7H₂O crystals, another cause of the change in mass on heating could be due to a chemical reaction taking place. Specifically, the magnesium sulfate could react with oxygen in the air to form magnesium oxide and sulfur trioxide, which are both lighter than the original compound. Additionally, if the heating is not done in a closed system, the gaseous products of the reaction, if any, might escape leading to a decrease in the total mass. For example, in the reaction when solid metallic magnesium reacts with hydrochloric acid, bubbles of hydrogen gas (H2) are evolved which could decrease the mass if it escapes.
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