College Chemistry : Solubility Rules and Precipitates

Study concepts, example questions & explanations for College Chemistry

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Example Questions

Example Question #1 : Solubility Rules And Precipitates

Write an equation for the precipitation reaction that occurs (if it occurs) when a solution of strontium chloride is mixed with a solution of lithium phosphate.

Possible Answers:

Correct answer:

Explanation:

Start by writing out the the chemical formulas for the reactants:

In order to figure out the possible products, combine the cation of one molecule with the anion of the other molecule.

For this reaction, the possible products are  and .

Next, use solubility rules to figure out if any precipitate is formed. Since compounds with are soluble,  is soluble. Since  is only soluble when paired with  is insoluble.

Thus, we can write the final chemical equation:

Example Question #2 : Solubility Rules And Precipitates

Which of the following is insoluble in water?

Possible Answers:

Correct answer:

Explanation:

Recall the solubility rules:

 is generally soluble, except when paired with .

 

Example Question #3 : Solubility Rules And Precipitates

Which of the following substances is insoluble in aqueous solution?

Possible Answers:

Correct answer:

Explanation:

Solubility rules can help us find the answer to this question. 

First, solubility rules state that all compounds of Group 1A elements on the periodic table are soluble in aqueous solution. This means that all of the alkali metals, including potassium, form compounds which are soluble in aqueous solution; thus,  is soluble in aqueous solution.

Solubility rules also tell us that all ammonium salts (salts of ) are soluble. This means that  is soluble.

Next, solubility rules tell us that all bromide salts are soluble, except for those of , and . Thus,  is not soluble in aqueous solution. However, as lithium is not included in that list,  is soluble in aqueous solution.

Example Question #4 : Solubility Rules And Precipitates

Which of the following is not readily soluble in water?

Possible Answers:

Correct answer:

Explanation:

Remember the solubility rules for ionic solids in water:

1) Salts of group 1 (with few exceptions) and NH4are soluble

2) Nitrates, acetates, and perchlorates are soluble

3) Salts of silver, lead, and mercury (I) are insoluble

4) Chlorides, iodides, and bromides are soluble

5) Carbonates, phosphates, sulfides, oxides, and hydroxides are insoluble. Exceptions: sulfides of group 2 cations and hydroxides of calcium, strontium, and barium are slightly soluble

6) Sulfates are soluble except for those of calcium, strontium, and barium

Following these rules, we see that MgOH is insoluble in water

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