High School Chemistry : Identifying Precipitates

Study concepts, example questions & explanations for High School Chemistry

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Example Questions

Example Question #11 : Solutions And Mixtures

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

\(\displaystyle Ag_{2}SO_{4}\)\(\displaystyle NH_{4}Cl\), \(\displaystyle KNO_{3}\)

Which salt will precipitate out of this solution?

Possible Answers:

\(\displaystyle KCl\)

\(\displaystyle AgNO_{3}\)

\(\displaystyle K_{2}SO_{4}\)

\(\displaystyle AgCl\)

Correct answer:

\(\displaystyle AgCl\)

Explanation:

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

\(\displaystyle Ag_2SO_4\rightarrow 2Ag^++SO_4^{2-}\)

\(\displaystyle NH_4Cl\rightarrow NH_4^++Cl^-\)

\(\displaystyle KNO_3\rightarrow K^++NO_3^-\)

Chloride compounds are generally soluble, but the salt \(\displaystyle AgCl\) 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 \(\displaystyle AgSO_4\), which is also insoluble.

Example Question #2 : Identifying Precipitates

What is the precipitate in the following aqueous reaction?

\(\displaystyle \small \small AgNO_3 + NaCl \rightarrow AgCl + NaNO_3\)

Possible Answers:

There is no precipitate; all compounds are soluble

\(\displaystyle NaNO_3\)

\(\displaystyle AgNO_3\)

\(\displaystyle AgCl\)

\(\displaystyle NaCl\)

Correct answer:

\(\displaystyle AgCl\)

Explanation:

The precipitate will be the product that is insoluble in water, so your choices are \(\displaystyle AgCl\) or \(\displaystyle NaNO_3\).

Nitrate salts are always soluble in water, as are alkali metal salts such as sodium. Thus, we know that \(\displaystyle NaNO_3\) 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, \(\displaystyle AgCl\), insoluble in water. \(\displaystyle AgCl\) is the precipitate.

Example Question #3 : Identifying Precipitates

What is the precipitate in the following aqueous reaction?

\(\displaystyle \small BaCl_2 + Na_2SO_4 \rightarrow BaSO_4 + NaCl\)

Possible Answers:

\(\displaystyle NaCl\)

\(\displaystyle BaCl_2\)

\(\displaystyle BaSO_4\)

\(\displaystyle Na_2SO_4\)

\(\displaystyle BaSO_4\ \text{and}\ NaCl\)

Correct answer:

\(\displaystyle BaSO_4\)

Explanation:

The precipitate will be the product that is insoluble in water. The products in this reaction are \(\displaystyle BaSO_4\) and \(\displaystyle NaCl\).

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

Sulfate salts are soluble in water, unless combined with silver, calcium, strontium, barium, or lead ions. In this case, \(\displaystyle BaSO_4\) is insoluble and is, therefore, the precipitate.

Example Question #11 : Solutions And Mixtures

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

Possible Answers:

An iron fence rusted

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

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 #12 : Solutions And Mixtures

Which phase label subscript is associated with an insoluble compound?

Possible Answers:

(r)

(g)

(s)

(aq)

(l)

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: \(\displaystyle H_2O_{(s)}\).

Example Question #6 : Identifying Precipitates

What is the precipitate in the following aqueous reaction?

\(\displaystyle \small \small AgNO_3 + NaCl \rightarrow AgCl + NaNO_3\)

Possible Answers:

\(\displaystyle NaNO_3\)

\(\displaystyle AgNO_3\)

There is no precipitate; all compounds are soluble

\(\displaystyle AgCl\)

Correct answer:

\(\displaystyle AgCl\)

Explanation:

The precipitate will be the product that is insoluble in water, so your choices are \(\displaystyle AgCl\) or \(\displaystyle NaNO_3\).

Nitrate salts are always soluble in water, as are alkali metal salts such as sodium. Thus, we know that \(\displaystyle NaNO_3\) 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, \(\displaystyle AgCl\), insoluble in water. \(\displaystyle AgCl\) is the precipitate.

Example Question #2 : Identifying Precipitates

What is the precipitate in the following aqueous reaction?

\(\displaystyle \small \small AgNO_3 + NaCl \rightarrow AgCl + NaNO_3\)

Possible Answers:

\(\displaystyle NaNO_3\)

\(\displaystyle AgNO_3\)

\(\displaystyle AgCl\)

There is no precipitate; all compounds are soluble

Correct answer:

\(\displaystyle AgCl\)

Explanation:

The precipitate will be the product that is insoluble in water, so your choices are \(\displaystyle AgCl\) or \(\displaystyle NaNO_3\).

Nitrate salts are always soluble in water, as are alkali metal salts such as sodium. Thus, we know that \(\displaystyle NaNO_3\) 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, \(\displaystyle AgCl\), insoluble in water. \(\displaystyle AgCl\) is the precipitate.

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