Complete and balance each gas-evolution equation.

Solution: Here, we are going to calculate the percentage by mass of magnesium hydroxide in the given sample. Step1: Given, the volume of NaOH solution used = 19.85 mL = 19.85 / 1000 L = 0.01985 L The molarity of NaOH solution used = 0.1020 M Therefore, number of moles of NaOH solution = Volume of solution in litres X Molarity = 0.01985 L X 0.1020 M = 0.002 mol Step2: Again, the volume of HCl solution used = 100.0 mL = 100 / 1000 L = 0.100 L The molarity of HCl solution used = 0.2050 M Therefore, number of moles of HCl solution = Volume of solution in litres X Molarity = 0.100 L X 0.2050 M = 0.0205 mol Since, 1 mole of NaOH will react with 1 mole of HCl for complete neutralisation, therefore, 0.002 mol of NaOH will react will 0.002 mol of HCl for neutralization. Thus, number of moles of HCl reacted with magnesium hydroxide =...