Question

All alkali metals react with water to produce hydrogen gas and the corresponding alkali metal hydroxide. A typical reaction is that between lithium and water: 2Li(s) + 2H2O(1) 2LiOH(aq) + H2(g) How many grams of Li are needed to produce 9.89 g of H₂ ?

Answer 1

69.23g

Step-by-step explanation:

Find out how many moles is in 9.89g of H2.

number of moles = mass(g) / molar mass

1 is the molar mass of hydrogen (to the nearest whole)

relative molecular mass of H2: 2*1 = 2

number of moles of H2 = 9.89/2 = 4.945

1 mol of H2 is produced from 2 mol of Li

so

4.945 mol of H2 produces 9.89 mol of Li

mass(g) = number of moles * molar mass

7 is the molar mass of Lithium (to the nearest whole)

mass = 9.89 * 7 = 69.23

69.23 grams of Li are needed to produce 9.89 of H2