Question

A toothpaste contains 0.228% by mass sodium fluoride used to prevent dental caries and 0.31% by mass triclosan C12H7Cl3O2, an antigingivities agent. One tube contains 119 g of toothpaste. (Express answer using 3 significant figures)

1. How many moles of NaF aew in the tube of toothpaste?

2. How many fluoride ions, F-, are in the tube of toothpaste?

3. How many grams of sodium ion, Na+, are in 2.45 g of toothpaste?

4. How many molecules of triclosan are in the tube of toothpaste?

Answer 1

Q1

moles of NaF in toothpaste

mass of NaF = 0.228/100*119 = 0.27132 g of NaF

mol = mass/MW = 0.27132/41.98817248

mol of NaF = 0.006461

Q2.

1 mol of F- per 1 mol of NaF

0.006461 mol of NaF = 0.006461 mol of F-

Q3

mass of Na+ in 2.45 g

mol of NaF in 119 g --> 0.006461

mol of NaF in 2.45 --> 2.45/119*0.006461 = 0.0001330 mol of NaF

mol of Na in NaF = 1:1 ratio

0.0001330 mol of Na+

mass = mol*MW = 0.0001330*23 = 0.003059 g = 3.059 mg

Q4

triclosan in tube

mass = 0.31/199*119 = 0.18537 g of C12H7Cl3O2

mol = mass/MW = 0.18537/289.5418 = 0.0006402 mol

1 mol = 6.022*10^23

molecules= (0.0006402)(6.022*10^23) = 3.8552*10^20 molecules