Chemistry 20 Question?

Question

I have forgotten many things, and help would be greatly appreciated.

Copper(II) chloride tetrahydrate = Formula

FeCr2O7 = Chemical Name

barium dihydrogen phosphate = Formula

I'm having trouble doing this because there are three elements, so a quick explaination would help.

Thanks in advance :D

Answer 1

Copper(II) chloride tetrahydrate

Whenever a chemical name is followed by "[prefix]-hydrate", first ignore this last part of the name; hence, write CuCl2. Then, consider that last word - it indicates that there are a number of water molecules corresponding to the prefix - four in this case. The formula is CuCl2 · 4H2O.

FeCr2O7: The two elements chromium and oxygen together form a polyatomic ion, Cr2O7(2-), which is known as the dichromate ion. Since it has a -2 charge, the iron must have a +2 charge. Therefore, the name is iron(II) dichromate.

Barium dihydrogen phosphate: "Dihydrogen phosphate" is a polyatomic ion formed by adding two H+ units to the phosphate ion, PO4(3-). Therefore, the ion has formula H2PO4-. Since barium takes the +2 state, the formula is Ba(H2PO4)2.

Answer 2

When a compound has a hydrate at the end, the formula doesn't change what you add is just a dot then the number of hydrates ( water molecules)

eg copper (II)chloride is CuCl2 and tetra means 4 so there are 4 water molecule ie 4H2O so the formula is CuCl2.4H2O

Am not sure u have written the second formular well but if its Fe2(Cr2O7)3 then its iron (III) dichromate

Phosphate has a valency of 3- and dihydrogen of 2+ when they combine they form (H2PO4) with a valency of 1- ( since H is dihydrogen). Barium as a valency of 2+ so when it combines with this anion it forms: Ba(H2PO4)2.



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