Question

Among the electrolytes na2so4, cacl2, al2(so4)3 and nh4cl, the most effective coagulating agent for sb2s3 sol is

Answer 1

This amounts to finding the atomic weight of the metal and the charge on the cation (in effect identifying the metal itself).

I didn't know how to do this, so I looked up the solution. It goes as follows.

Solution

Assume the oxide has the formula MO. Let the atomic weight of M be x Then

16x+16=40100

Simplifying and solving for x yields

x=24

Thus the metal is magnesium and the equivalent weight is 12.

My problem is, how can we assume that the metallic oxide has the formula MO? For all we know, the metallic oxide may be M2O or M2O3. In fact, if we assume the latter formula we get

482x+48=40100