This is the chemical formula for talc (the main ingredient in talcum powder):
mg3( si2o5)2(oh)2
an analytical chemist has determined by measurements that there are 21.4 moles of magnesium in a sample of talc. how many moles of silicon are in the sample?

28.53 moles of silicon

Explanation:

Chemical formula helps us to see which elements are contained in a compound. If correctly written, it can also help us see how much atoms of each element are there.

For this particular case, in one molecule of talc, we have;

3 atoms of Mg

4 atoms of Si

12 atoms of O

2 atoms of H

From here, we can find the ratio of any two atoms from the molecule. So, we can say that the ratio of Mg: H is 3:2, or that ratio of O: Mg is 12:3 etc.

Now, if we expand this concept on moles, we can easily solve this problem.

We know there are 21.4 moles of Mg and want to know how many moles of Si are there. Since we can see the ratio of Mg: Si which is 3:4, we write a proportion:

3 : 4 = 21.4 : x

x = 21.4 • 4 / 3

x = 28.53 moles of Si