Chemistry Quiz 4 Review Questions

What does it mean for a compound to be soluble? Insoluble?

A compound is soluble if it dissolves in water. A compound is insoluble if it does not dissolve in water.

Explain how a molecule equation, a complete ionic equation and a net ionic equation differ.

A molecular equation shows the complete neutral formulas for each compound in the reaction as if they existed as molecules. Equations that list individually all of the ions present as either reactants or products in a chemical reaction are complete ionic equations. Equations that show only the species that actually change during the reaction are net ionic equations.

What is a preciptation reaction? Give an example.

A precipitation reaction is one in which a solid or precipitate forms upon mixing two solutions. An example is 2KI(aq) + Pb(NO3)2 (aq) --> Pb2I (s) + 2KNO3 (aq).

Explain the difference between a strong acid and a weak acid.

Acids are molecular compounds that ionize-form ions- when they are dissolve in water. A strong acid completely ionizes in solution. A weak acid does not completely ionize in water. A solution of a weak acid is compose mostly of the nonionized acid.

What is an aqueous solution? What is the difference between the solute and solvent?

An aqueous solution is a solution in which water acts as a solvent. The solvent is the majority component of the mixture, and the solute is the minority component of the mixture.

What are the cations and anions whose compounds are really soluble? What are the exceptions? What are the anions whose compounds are mostly insoluble? What are the exceptions?

Cations that usually form soluble compounds are Li+, K+, NH4+. The anions that usually form solute compounds are NO3- and C2H3O2-, which have no exceptions; Cl-, Br-, and I- except with Sr 2+, Ba2+, Pb 2+, Ag + or Ca 2+, which form insoluble compounds. The anions that usually form insoluble compounds are OH- and S2- except with Li+, Na+, K+ or NH4+, which form soluble compounds; and when S2- pairs with Ca2+, Sr 2+ or Ba 2+, which form soluble compounds; CO3 2- and PO4 3- are insoluble except when paired with Li+, Na+, K+, NH4+.

What is molarity? How is it useful?

Molarity is a concentration term. It is the amount of solute (in moles) divided by the volume of solution (in liters). The molarity of a solution can be used as a conversion factor moles of the solute and liters of the solution.

We typically calculate the percent yield using the actual yield and theoretical yield in units of mass (g or kg). Would the percent yield be different if the actual yield and theoretical yield were in units of amount (moles)?

No, the percent yield will not be different if the actual yield and theoretical yield were calculated in moles. The relationship betweens grams and moles is the molar mass. This would be the same value for the actual yield and theoretical yield.

What is reaction stoichiometry? What is the significance of the coefficients in a balanced chemical equation?

Reaction stoichiometry is the numerical relationship between chemical amounts in a balanced chemical equation. The coefficients in a chemical reaction specify the relative amounts of moles in each of the substances involved in the reaction.

Explain how a strong electrolyte, a weal electrolyte and a non-electrolyte differ.

Substances the completely dissociate into ions when they dissolve in water are called strong electrolytes and conduct electricity easily. Substances that do not completely dissociate in water are called weak electrolytes and conduct electricity only weakly. Compounds that do not dissociate into ions when dissolved in water are called non electrolytes and do not conduct electricity.

What are the solubility rules? How are they useful?

The solubility rules are a set of empirical rules that have been inferred from observations about many ionic compounds. The solubility rules allow us to predict whether a compound is soluble or insoluble.

How can you predict whether a precipitation reaction will occur upon mixing two aqueous solutions?

The key to prediction precipitation reactions is to understand that only insoluble compounds form precipitates. In a precipitation reaction, two solutions containing soluble compounds combine and an insoluble compound precipitates.

In a chemical reaction, what is the limiting reactant? The theoretical yield? The percent yield? What do we mean when we say reactant is in excess?

The limiting reactant is the reactant that is completely consumed in a chemical reaction and limits the amount of product. The theoretical yield is the amount of product that can be made in a chemical reaction based on the amount of limiting reactant. The percent yield can be calculated as (actual yield)/(theoretical yield) x 100%. The reactant in excess is any reactant that occurs in a quantity greater than that required to completely react with the limiting reactant. Some of this reactant will be left over when the reaction is complete.