[rlsheley]

I'm currently reviewing general chemistry I from my textbook, as I have not taken in in several years and will be taking gen chem II soon. I don't really have a professor to ask at the moment, so I turn to you, internet...

In the book, one of the questions asked what will happen if we add HCl to MgO, and to write a balanced chemical equation and net equation.

I first got MgO(s) + HCl(aq) --> MgCl(aq) + OH-(aq), which I know couldn't be right (I didn't balance it because it looked wrong). It turns out MgO is a base, so it produces MgCl(aq) + H₂O(l) when reacting with HCl. The net ionic equation is MgO(s) + 2H⁺ --> Mg²⁺(aq) + H₂O(l).

Here are my questions:
1. How do I know MgO is a base? I was thinking it was a salt, so this one stumped me.
2. How would I go about formulating the full equation without "just knowing" it produces a salt and water? Basically, could anyone show me how mathematically, I would get MgCl + H₂O out of MgCl + OH^-?
3. Moreover, how do I tell if ANY compound is an acid/base? I get the H and OH thing, but MgO doesn't have an OH (like Mg(OH)₂). I'm trying to write down a huge list of ways to tell what a compound is so I can figure out how it reacts, and maybe someone has a resource for that?

Thank you so much!!!

[Borek]

1. How do I know MgO is a base? I was thinking it was a salt, so this one stumped me.

MgO is an oxide. Many metal oxides react with water producing hydroxides, so they are basic in nature. That's especially true for elements from first two groups.

2. How would I go about formulating the full equation without "just knowing" it produces a salt and water? Basically, could anyone show me how mathematically, I would get MgCl + H₂O out of MgCl + OH^-?

No way, you need to know the basic reaction types.

3. Moreover, how do I tell if ANY compound is an acid/base? I get the H and OH thing, but MgO doesn't have an OH (like Mg(OH)₂). I'm trying to write down a huge list of ways to tell what a compound is so I can figure out how it reacts, and maybe someone has a resource for that?

Metal oxides tend to react with water producing hydroxides, non-metal oxides tend to react with water producing acids, some elements (more or less those on the diagonal of the periodic table) are amphoteric and can behave both ways. This is just a rule of thumb, but in most simple cases a good starting point.

[AWK]

I am sure that magnesium chloride is presented with different formula in your textbook.