posted by j .
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?
Start from the equation
Li + H2O -> LiOH + H2
which you will need to balance.
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.