High School Chemistry : Identifying Precipitates

Study concepts, example questions & explanations for High School Chemistry

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Example Questions

Example Question #1 : Identifying Precipitates

A solution is created by adding all of the following soluble salts to water:

,

Which salt will precipitate out of this solution?

Possible Answers:

Correct answer:

Explanation:

All of the three salts will dissolve completely in the solution, resulting in all of the ions interacting with one another.

Chloride compounds are generally soluble, but the salt  is one of the notable insoluble chloride salts. When these two ions meet in solution, they will combine and precipitate out of the solution. All the other ion combinations still form soluble compounds except for , which is also insoluble.

Example Question #2 : Identifying Precipitates

What is the precipitate in the following aqueous reaction?

Possible Answers:

There is no precipitate; all compounds are soluble

Correct answer:

Explanation:

The precipitate will be the product that is insoluble in water, so your choices are  or .

Nitrate salts are always soluble in water, as are alkali metal salts such as sodium. Thus, we know that  will fully dissolve.

Halide salts (such as chlorides) are soluble in water, unless they are combined with silver, lead, or mercury. In this case, the silver atom makes the halide salt, , insoluble in water.  is the precipitate.

Example Question #3 : Identifying Precipitates

What is the precipitate in the following aqueous reaction?

Possible Answers:

Correct answer:

Explanation:

The precipitate will be the product that is insoluble in water. The products in this reaction are  and .

Halide salts (such as chlorides) are soluble in water, unless combined with silver, lead, or mercury. In this case,  is soluble in water.

Sulfate salts are soluble in water, unless combined with silver, calcium, strontium, barium, or lead ions. In this case,  is insoluble and is, therefore, the precipitate.

Example Question #4 : Identifying Precipitates

Which of the following is not an example of a chemical change?

Possible Answers:

A cup of water left in the freezer turned into ice

A wood log gets turned to ashes after burning

A precipitate formed during the mixing of two substances

An iron fence rusted

Bubbles formed after adding a salt to an acid

Correct answer:

A cup of water left in the freezer turned into ice

Explanation:

Water turning to ice is not a chemical reaction, it is a physical reaction. Nothing is changing about the water molecules chemically, they're just going from a liquid state to a solid state. Burning wood is a non-reversible chemical change because the carbon in the wood is reacting with oxygen to create ash and smoke, also, energy in the form of light and heat is released. Rust is formed when iron reacts chemically with oxygen, producing the red-orange color of rust. A gas forming is a good indicator that a chemical reaction has taken place. A precipitate is also a good indicator for a chemical reaction. It may just seem like something is changing states, but the precipitate is not a solid version of one of the reactants, it's the insoluble product formed from the chemical reaction.

Example Question #5 : Identifying Precipitates

Which phase label subscript is associated with an insoluble compound?

Possible Answers:

(l)

(r)

(g)

(s)

(aq)

Correct answer:

(s)

Explanation:

If something is insoluble, it means it cannot be dissolved. The phase label reserved for solids is (s). The other phase labels are: (l) = liquid; (aq) = aqueous; (g) = gas; and the (r) phase label does not exist. Note that all of the phase labels are written as subscripts after the species; for example: .

Example Question #6 : Identifying Precipitates

What is the precipitate in the following aqueous reaction?

Possible Answers:

There is no precipitate; all compounds are soluble

Correct answer:

Explanation:

The precipitate will be the product that is insoluble in water, so your choices are  or .

Nitrate salts are always soluble in water, as are alkali metal salts such as sodium. Thus, we know that  will fully dissolve.

Halide salts (such as chlorides) are soluble in water, unless they are combined with silver, lead, or mercury. In this case, the silver atom makes the halide salt, , insoluble in water.  is the precipitate.

Example Question #7 : Identifying Precipitates

What is the precipitate in the following aqueous reaction?

Possible Answers:

There is no precipitate; all compounds are soluble

Correct answer:

Explanation:

The precipitate will be the product that is insoluble in water, so your choices are  or .

Nitrate salts are always soluble in water, as are alkali metal salts such as sodium. Thus, we know that  will fully dissolve.

Halide salts (such as chlorides) are soluble in water, unless they are combined with silver, lead, or mercury. In this case, the silver atom makes the halide salt, , insoluble in water.  is the precipitate.

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