Solubility Rules - Chemistry LibreTexts

Problems

1. Is FeCO3 soluble?

According to Rule #5, carbonates tend to be insoluble. Therefore, FeCO3 is likely to form a precipitate.

2. Does ClO4- tend to form a precipitate?

This is perchlorate, which according to Rule #2 is likely to be soluble. Therefore, it will not form a precipitate.

3. Which of these substances is likely to form a precipitate?

a) CaSO4 b) table salt c) AgBr

Letters a and c are both likely to form precipitates.

Concerning a) CaSO4​, although sulfates tend to be soluble, Rule #5 indicates that calcium sulfate is an important exception to this rule.

For b), Rule #1 indicates that table salt (NaCl) is soluble because it is a salt of an alkali metal.

c) is an example of two rules contradicting each other. Rule #4 states that bromides are usually soluble, but Rule #3 states that salts of silver are insoluble. Because Rule #3 precedes Rule #4, the compound is insoluble and will form a precipitate.

4. Predict whether a precipitate will form as a result of this reaction:

\[2AgNO_3 + Na_2S \rightarrow Ag_2S + 2NaNO_3 \]

The products of the reaction must be examined; if either of the substances formed in the reaction is insoluble, a precipitate will form.

Considering NaNO3, Rule #3 states that nitrates tend to be soluble. A precipitate of this compound will not form.

Next, consider Ag2S. According to Rule #5, that sulfides tend to be insoluble. Therefore, because of this compound, a precipitate will form in the course of this reaction.

5. Predict if a precipitate will form as a result of this reaction:

\[2NaOH + K_2CrO_4 \rightarrow KOH + Na_2CrO_4 \]

Consider again the products of the reaction: if either is insoluble, a precipitate will form.

The first product, KOH, is an example of two rules contradicting each other. Although Rule #5 says that hydroxides tend to be insoluble, Rule #1 states that salts of alkali metal cations tend to be soluble, and Rule #1 precedes Rule #5. Therefore, this compound will not contribute to any precipitation being formed.

The second product, Na2CrO4, also adheres to Rule #1, which states that salts of alkali metals tend to be soluble.

Because both products are soluble, no precipitate form as a result of this reaction.