# A brand of toothpaste contains 0.22% by mass sodium flouride (NaF). Calculate the mass of flouride ions in a tube containing 120g of the paste.

justaguide | College Teacher | (Level 2) Distinguished Educator

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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.

alageegee | Student | (Level 1) eNoter

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22% = 120g of NaF per 100g of toothpaste

in 120g m(NaF)=0.22 x 120/100
m(NaF)= 0.264 g

n(NaF)= 0.264/41.9
n(NaF)=0.006287 mole

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