Question

 

1. A sample of a compound has a mass of 4.86 g and is composed of Silicon and Oxygen. What is the percent composition if 2.27 g of the mass is Silicon?

2. What is the percent composition of all of the elements in saccharin (C7H5SNO3)?

3. What is the mass of phosphorus in a 25.0lb quantity of sodium phosphate?

Answer 1

1.

Total mass of the compound = 4.86 g.

Mass of silicon in that compound = 2.27 g.

Percent composition of silicon = (Mass of silicon / Mass of compound) x 100

= (2.27 / 4.86) x 100

= 46.7%

Thus, the percent composition of silicon = 46.7%

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2.

Given, molecular formula of Saccharin = C7H5SNO3.

The molar mass of Saccharin = 183 g/mol

Percent composition of Carbon:

The molar mass of Carbon = 12 g/mol

There are seven carbons in Saccharin.

So, mass of carbon in saccharin = 12 x 7 = 84g.

Percent = (Mass of carbon / Mass of saccharin) x 100 = (84/183) x 100 = 45.90 %

Percent composition of Hydrogen:

The molar mass of Hydrogen = 1 g/mol

There are five carbons in Saccharin.

So, mass of hydrogen in saccharin = 1 x 5 = 5g.

Percent = (Mass of hydrogen / Mass of saccharin) x 100 = (5/183) x 100 = 2.73 %

Percent composition of Sulfur:

The molar mass of Sulfur = 32 g/mol

There is one sulfur in Saccharin.

So, mass of sulfur in saccharin = 32 x 1 = 32g.

Percent = (Mass of sulfur / Mass of saccharin) x 100 = (32/183) x 100 = 17.4 %

Percent composition of Nitrogen:

The molar mass of Carbon = 14 g/mol

There is one nitrogen in Saccharin.

So, mass of nitrogen in saccharin = 14 x 1 = 14g.

Percent = (Mass of nitrogen / Mass of saccharin) x 100 = (14/183) x 100 = 7.65 %

Percent composition of Oxygen:

The molar mass of Oxygen = 16 g/mol

There are three oxygens in Saccharin.

So, mass of carbon in saccharin = 16 x 3 = 48g.

Percent = (Mass of oxygen / Mass of saccharin) x 100 = (48/183) x 100 = 26.23%

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3.

The molecular formula of sodium phosphate = Na3PO4.

The molar mass of sodium phosphate = 163.94 g/mol.

Mass of phosphorous = 31 g/mol

Given, mass = 25.0 lb.

1lb = 453.592 g

25.0 lb = 453.592 x 25.0 = 11339.8 g

So, 163.94 g of Sodium phosphate contains 31 g of Phosphorous.

11339.8 g of Sodium phosphate cotains (11339.8 x 31) / 163.94 = 2144.28 g of Phosphourus.