Hey! My name is Freddy, and today, I will teach you about Percentage Composition.

Percentage Composition is the percentage by mass of each element in a compound.

% Composition = mass of an element/total mass x 100. You multiply by 100 to make the composition into a percentage out of 100

Now, let's tackle a problem. We'll start by finding the percentage composition of Copper Sulfide.

Copper Sulfide's formula is Cu2S. First, we will start with Copper. Copper's mass is 63.546 grams.

Since "Cu" has a "2" after it, you multiply the mass by 2! This makes the mass of the element 127.092.

Now that we have the numerator that we are going to divide by, we now need to find the denominator. 

The denominator of this equation is the total mass. This means we need to add Cu2+S. Sulfur's mass is 32.07.

Sulfur's mass, 32.07 + Copper's mass (x2) = 159.17 grams Cu2S.

Now we divide! 

127.10 grams Cu/159.17 grams Cu2S

127.10 grams Cu divided by 159.17 grams Cu2S = 0.79852