Theory or Reality - Acid/base trends on the periodic table

[Qube]

Homework Statement

Number 12. Ignore the scribbling and the circled answers.

http://i.minus.com/i17OAHo9PELaW.jpg

Homework Equations

The periodic table trend of acid/base behavior says that oxides of elements on the right of the periodic table will behave as acids in water. It says that oxides of elements on the left of the periodic table will behave as bases in water (metal hydroxides).

The Attempt at a Solution

I know that SO3 and P4O10 will dissolve in water to form a strong and weak acid, respectively. The metal oxide MgO will form a metal hydroxide. However, I'm not sure what happens to Bi2O3. It's definitely on the right side of the periodic table, so I would expect it to form an acid. However, according to Wikipedia, it is insoluble in water. We were not taught exceptions in class (at least to the periodic trend of acid/base behavior). What would your take be on this question?

 

[Borek]

What would your take be on this question?

I don't like the question, as it is confusing and ambiguous. Bismuth is amphoteric, so the idea that Bi₂O₃ can dissolve in water producing traces of acid is quite reasonable. I doubt it would substantially change pH of the solution, so I would go with II and IV (answer 2).

 

[frozonecom]

No, even if it is on the right side of the periodic table, it is classified as a metal. Most metal oxides are basic. Also, insoluble is a very confusing term. I guess what wikipedia wanted to say is that it is /sparingly soluble/, meaning it does dissolve in water, but only to a minimum, often negligible extent. So, when Bi2O3 does dissolve in water, it will behave as a base.

The general rule is metal oxides behaves as base when dissolved and nonmetal oxides will behave as an acid when dissolved.

The periodic trends help us to form ideas about the behaviors/properties of compounds. However, I think you should never solely rely on it. Because, as you said, there are many exemptions to the trends.

 

[Borek]

it is classified as a metal

Or metalloid, or near metalloid, depending on whom you listen to.

It is closer to metals than to non-metals, but there is also no doubt about its amphotericity.

Actually, the longer I think about it, the less I am sure about its exact properties. Unfortunately, I don't have my inorganic chemistry textbooks here ATM :\