Unit 2 Chemistry Review

Distinguish between a 1M solution and a 1m solution.

1M solution: 1 mol of solute in 1 L of solution; 1m solution: 1 mol of solute in 1000 g of solvent

What is a Lewis acid? A Lewis base? In what sense is the Lewis theory more general than the Arrhenius and Brønsted-Lowry theories?

A Lewis acid accepts a pair of electrons to form a covalent bond. A Lewis base donates a pair of electrons to form a covalent bond. The Lewis theory explains the behavior of compounds that act like bases without accepting hydrogen ions or that act like acids without donating hydrogen ions.

Would a strong acid have a large or a small Ka? Explain

A strong acid is completely dissociated;Ka must be large.

How did Arrhenius describe acids and bases?

Acids ionize to give hydrogen ions in aqueous solution. Bases ionize to give hydroxide ions in aqueous solution.

What are colligative properties? Identify three colligative properties and explain why each occurs

Colligative properties are properties of a solution that depend only on the number of solute particles; boiling-point elevation, freezing-point depression, and vapor- pressure lowering. Boiling points are elevated because shells of solvent form around solute particles, reducing the amount of solvent molecules that have sufficient energy to escape the solution; relative to the pure solvent, the amount of energy required to cause vaporization or boiling increases. Solutes disrupt the ordering of the solvent structure, so more kinetic energy must be withdrawn from a solution for it to solidify. This lowers the freezing point of the solution.

Knowing the molarity of a solution is more meaningful than knowing whether a solution is dilute or concentrated. Explain.

Diluteandconcentratedarerelativeterms and are not quantitative. Molarity provides the exact number of moles o

A buffered solution cannot absorb an unlimited amount of acid or base. Explain

Eventually the buffer capacity of the buffer is exceeded and the pH will change significantly with the addition of a strong acid or base.

Can a solution with undissolved solute be supersaturated? Explain

No; if there were undissolved solute, the excess solute would

If a saturated solution of sodium nitrate is cooled, what change might you observe?

Particles of solute crystallize

Explain why the dissolved component does not settle out of a solution.

Random collisions of the solvent molecules with the solute particles provide enough force to overcome gravity

What is the effect of pressure on the solubility of gases in liquids?

Solubility increases with pressure.

Why does a 1m solution of calcium nitrate have a lower freezing point than a 1m solution of sodium nitrate?

The effective molality of the Ca(NO3)2 solution is 3m. The effective molality of the NaNO3 solution is 2m

What is characteristic of the end point of a titration?

The indicator changes color.

In old-fashioned ice cream makers, a mixture of rock salt (NaCl) and ice is used to cool the creamy mixture as it is stirred. What is the purpose of the salt

The salt lowers the freezing point of the ice-water cooling mixture.

Explain why solutions of salts that hydrolyze water do not have a pH of 7.

Weakacidanionsacceptprotonsfrom water, increasing the pH of the solution. Weak base cations donate protons to water, decreasing the pH.

Explain how a decrease in the vapor pressure of a solution results in an increase in its boiling point

When vapor pressure is lowered relative to pure solvent, more energy must be supplied to reach the boiling point; thus the boiling point is increased relative to pure solvent.

Is it possible to have a concentrated weak acid? Explain

Yes, acids like acetic acid dissolve well but ionizepoorly.

What kinds of salts hydrolyze water?

salts with a cation from a weak base and an anion from a strong acid, or with a cation from a strong base and an anion from a weak acid

How is the pH of a solution calculated?

the negative logarithm of the [H+]