Good Morning and welcome to Chemistry.

We’ve been talking about the mole the last few days. Today, we are continuing with the mole theme and asking you to calculate the %composition of a substance. You’ll need a calculator and a periodic table.

For example: Water’s molar mass is 18 grams.

O = 16 g (The periodic table says 15.999 g, so we can do a little rounding)

H = 1 g x 2 = 2 g

Add 16+2 and the molar mass of water is 18 grams.

The percent by mass is {(mass of one element in the compound)/(molar mass of total compound)} x 100

(16/18) * 100 = 88.9% Oxygen

(2/18) * 100 = 11.1% Hydrogen.

They percentages should add up close to 100%.

I’d like you to find the percent by mass of each element in the following substances:

A. Aluminum Sulfate (see yesterday’s work for the formula)

B. Phosphoric Acid (H₃PO₄)

C. Calcium Chloride, CaCl₂

D. Ethane C₂H₆

E. The mineral Ilmenite, FeTiO₃ (Note: it contains Titanium)

Please show all work on paper and send a picture of your work to me in Remind.

Thanks,

Stay healthy and Stay Breezy.

T. Brown