The brand of toothpaste contains 0.22% by mass sodium fluoride. The mass of fluoride ions in a tube containing 120 g of toothpaste is to be determined.
The chemical formula of sodium fluoride is sodium fluoride. The mass of one mole of sodium fluoride is 41.99 g/mol
As the mass of the fluoride ion is 18.99, the percentage mass of sodium fluoride that is constituted by the fluoride ions is 18.99/41.99 = 0.4522
120 g of the tooth paste has 0.22% by mass of sodium fluoride. This gives the mass of sodium fluoride as 120*0.22/100 = 0.264 g. The mass of fluoride ions in this is 0.4522*0.264 = 0.12 g.
22% = 120g of NaF per 100g of toothpaste
in 120g m(NaF)=0.22 x 120/100
m(NaF)= 0.264 g
since 1 mol of NaF contains 1 mole of flouride ions
n(F) = 0.006287 mole
m(F)= n(F) x M(F)
m(F)= 0.006287 x 19
m(F)= 0.12 g