Begin by writing formulas for the reactants and products, including physical states. When necessary use coefficients to balance the equation. A) When solid sodium hydride, NaH, is added to water, hydrogen gas is released and aqueous sodium hydroxide forms.
B) Aluminum metal reacts with chlorine gas to form solid aluminum chloride.

NaH(s) + H₂O(aq) ⇒ NaOH (aq) + H₂ (g)

Al(s) + Cl₂(g) ⇒ AlCl₃(s)

Explanation:

NaH - sodium hydride

H₂O - water

NaOH - sodium hydroxide

Al - aluminium

Cl₂ - Chlorine

AlCl₃ - aluminium chloride

the role of the microscope world in creating new materials .

1. for the first question, we must find the mass of the anhydrous salt, mgso₄. the molar mass for mgso₄·7h₂o is 246.47 g/mol, while that of mgso₄ is 120.37 g/mol.7.834 g mgso₄·7h₂o * 1 mol mgso₄·7h₂o/246.47 g * 1 mol mgso₄/1 mol mgso₄·7h₂o * 20.37 g mgso₄/mol = 0.647 g mgso₄

2. mass of water = mass of sample - mass of anhydrous salemass of water = 7.834 - 0.647 = 7.19 gpercent water in hydrate = 7.19/7.834 * 100 = 91.74%