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### Concentration

Posted: **Fri Oct 19, 2018 11:54 pm**

by **Andrea- 3J**

"Determine the concentration of the solution made by dissolving 660g Ca3(PO4)2 in 2.5L of water."

concentration is moles/vol.

You must find the moles of Ca3(PO4)2 and then divide it by 2.5L.

How do you find moles of Ca3(PO4)2? Ca3(PO4)2 is a complicated compound so I don't understand how to find the molar mass.

### Re: Concentration

Posted: **Fri Oct 19, 2018 11:59 pm**

by **Emily Li 4A**

To find the molar mass, you first have to find the amount of each element used in the chemical formula. There are 3 moles of calcium. Since phosphate is doubled, there are 2 moles of phosphorus and 8 moles of oxygen. Multiply each of these numbers to the respective element's molar mass on the periodic table, and add them together. That should give you the molar mass of calcium phosphate; make sure to look out for significant figures on this question though! Don't round until the very end.

### Re: Concentration

Posted: **Sat Oct 20, 2018 12:02 am**

by **Caitlin_Murphy_3C**

To find the molar mass of Ca3(PO4)2, you need the molar mass of each element in the compound, which can be found on the periodic table. As for the subscript "2" outside of the parentheses (PO4), that needs to be distributed in.

So, for the compound Ca3(PO4)2, you would have a total of:

3 Calcium atoms

2 Phosphorus atoms (1x2=2)

8 Oxygen atoms (2x4=8)

you then multiply each of these values by its corresponding molar mass to get the total molar mass of the compound.

Hope this helped!