Inquiry lab inorganic compounds

Jan 2015

I am having a problem with the following: I need to find a way to identify 3 given solid compounds as either salt, hydroxide or acid.
I would start with measuring pH after dissolving in water. Low pH would mean it s no hydroxide, but it can still be an acid or a salt. Then I would determine melting point. Low melting point would identify the substance as an acid, high melting point would make it a salt.
When pH would be neutral, it would be a salt.
When pH is high it is a hydroxide or a salt. And that's where I am stuck. How can I discriminate between a hydroxide and a salt that reacts basic in water (like sodiumcarbonate)?