Convert 0.123kg sio2 to moles. use three significant figures

2.05 moles of SiO₂

Explanation:

1- The molar mass of the compound must be calculated. To do this, with the help of a periodic table the atomic weights of the elements of the compound are sought and the sum of them is performed:

mSiO₂= mSi + 2 x mO = 28.09 g + 2 x 15.99 g = 60.07 g / mol

2- Once the molar mass is obtained, you can calculate the number of moles that represent the amount of SiO₂ in the statement. Since the data is in units of kilograms, and the molecular mass that has been calculated is in grams, a unit conversion of some of the two data must be performed, to have them in the same unit. All data will be passed to grams.

So:

1 kg 1000 g

0.123 kg X = 123 g

Calculation: (0.123 kg x 1000g) / 1 kg = 123 g of sample

3- Now the mass of SiO₂ can be converted to moles:

60.07 g SiO₂ 1 mol

123 g SiO₂ X = 2.0476 mol

Calculation: (123 g x 1 mol) / 60.07 g = 2.0476 mol ≅ 2.05 mol

As the statement says that we use three significant figures, only three figures of the calculated result are left and according to the fourth figure obtained that is a 7, we round the last significant figure by adding a unit.

As a result, 0.123 kg of SiO₂ equivalent to 2.05 moles.