Question

Lithium metal dissolves in water to yield hydrogen gas and aqueous lithium hydroxide. What is the final concentration of hydroxide ions when 5.500 g of lithium metal is dropped into 750. mL of water?

Answer 1

Start from the equation

Li + H2O -> LiOH + H2

which you will need to balance.

In water

LiOH -> Li+ + OH-

so one mole of LiOH gives one mole of OH-. From the balanced equation you can work out how many moles of LiOH are obtained from one mole of Li metal.

Calculate the number of moles of Li metal

number of moles = 5.500 g/ RAM for Li

hence find number of moles of LiOH, which equals number of moles of OH-

[OH-] = number of moles of OH-/0.750 litre

take care with the significant figure as well.

Answer 2

1.06