Chemistry Chapter 19: Acids, Bases, and Salts; Chapter 16: Solutions
Write an equation for the reaction of each antacid with hydrochloric acid. - magnesium hydroxide - calcium carbonate - aluminum hydroxide
- 2HCl + Mg(OH)2 = MgCl2 + 2H2O - 2HCl + CaCO3 = H20 + CO2 + CaCl2 - Al(OH)3 + 3HCl = AlCl3 + 3H2O
16.4: Calculations Involving Colligative Properties
- Chemists use two ways to express the ratio of solute to solvent: in molality and in mole fractions. - The magnitudes of freezing-point depression and boiling-point elevation are proportional to molality. - Key Equations: Molality (m) = (moles of solute/kilogram of solvent) Mole fractions: Xa = (nA/nA + nB), Xb = (nB/na + nB) Delta Tf = Kf x m Delta Tb = Kb x m
16.3: Colligative Properties of Solutions
- Colligative properties of solutions include vapor-pressure lowering, freezing-point depression, and boiling-point elevation.
16.1: Properties of Solutions
- Factors that determine how fast a substance dissolves are stirring, temperature, and surface area. - In a saturated solution, a state of dynamic equilibrium exists between the solution and any undissolved solute, provided that the temperature remains constant. - Temperature affects the solubility of solid, liquid, and gaseous solutes in a solvent; both temperature and pressure affect the solubility of gaseous solutes. - Key Equation: Henry's law: (S1/P1) = (S2/P2)
Write the formula and name of the conjugate acid of each Bronsted-Lowry base. - ClO2- - H2O - H2PO4- - NH3
- HClO2, chlorous acid - H3O+, hydronium ion - H3PO4, phosphoric acid - NH4+, ammonium ion
Write equations showing that the hydrogen phosphate ion (HPO42-) is amphoteric.
- HPO42- = H+ + PO43- (acting as an acid) - HPO42- + H+ = H2PO4- (acting as a base)
Write the expression for Ka for each acid. Assume only one hydrogen is ionized. -HF -H2CO3
- Ka = ([H+][F-])/[HF] - Ka = ([H+][HCO-3])/[H2CO3]
16.2: Concentrations of Solutions
- To calculate the molarity of a solution, divide the moles of solute by the volume of the solution in liters. - Diluting a solution reduces the number of moles of solute per unit volume, but the total number of moles of solute in solution does not change. - Percent by volume is the ratio of the volume of solute to the volume of solution. Percent by mass is the ratio of the mass of the solute to the mass of the solution. - Key Equations: Molarity (M) = (moles of solute/liters of solution) M1 x V1 = M2 x V2 Percent by volume = (volume of solute/volume of solution) x 100% Percent by mass = (mass of solute/mass of solution) x 100%
Write balanced equations for the reaction of each metal with water. -lithium -barium
-2Li + 2H2O = 2LiOH + H2 -Ba + 2H2O = Ba(OH)2 + H2
19.1 Acid-Base Theories
-According to Arrhenius, acids are hydrogen-containing compounds that ionize to yield hydrogen ions in aqueous solutions. Bases are compounds that ionize to yield hydroxide ions in aqueous solution. -According to the Bronsted-Lowry theory, an acid is a hydrogen-ion donor and a base is a hydrogen-ion acceptor. -According to Lewis, an acid accepts a pair of electrons and a base donates a pair of electrons.
19.3: Strength of Acids and Bases
-Acids and bases are classified as strong or weak based on the degree to which they ionize in water. Key Equation: Ka=([H+][A-])/[HA]
19.2: Hydrogen Ions and Acidity
-For aqueous solutions, the product of the hydrogen-ion concentration and the hydroxide-ion concentration equals 1 x 10^-14. -A solution with a pH less than 7.0 is acidic. A solution with a pH of 7 is neutral. A solution with a pH greater than 7.0 is basic. -Either acid-base indicators or pH meters can be used to measure pH. Key Equations: Kw = [H+] x [OH-] = 1.0 x 10^-14 pH = -log[H+]
19.4: Neutralization Reactions
-In general, acids and bases react to produce a salt and water. -Neutralization occurs when the number of moles of hydrogen ions is equal to the number of moles of hydroxide ions.
Write an equation for the dissociation of each compound in water. -KOH -Mg(OH)2
-KOH = K+ + OH- -Mg(OH)2 = Mg2+ + 2OH-
19.5: Salts in Solution
-Salts that produce acidic solutions have positive ions that release hydrogen ions to water. Salts that produce basic solutions have negative ions that attract hydrogen ions from water. -A buffer is a solution of a weak acid and one of its salts or a weak base and one of its salts.
Classify each compound as an Arrhenius acid or an Arrhenius base. -Ca(OH)2 -C2H5COOH -HNO3 -KOH -HBr -H2SO4
-base -acid -acid -base -acid -acid
Predict whether an aqueous solution of each salt will be acidic, basic, or neutral. -NaHCO3 -NH4NO3 -KCl -Na2CO3 -Na2SO4 -NH4Cl
-basic -acidic -neutral -basic -neutral -acidic
Identify each compound as a strong or weak acid or base. -NaOH -NH3 -H2SO4 -HCl
-strong base -weak base -strong acid -strong acid
What are the concentrations of H+ and OH- in pure water at 25 degrees Celsius?
1.0 x 10^-7 M for both H+ and OH- at 25 degrees Celsius
What is a Lewis acid? What is a Lewis base?
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.
What are the components of a buffer?
A buffer is a solution of a weak acid and one of its salts or a solution of a weak base and one of its salts.
Immiscible
A description of two liquids that are insoluble in one another
Miscible
A description of two liquids that dissolve in each other in all proportions; in such a solution, the liquid that is present in the larger amount is usually considered the solvent
Concentration
A measure of the amount of solute that is dissolved in a given quantity of solvent
Colligative property
A property of solutions that depends only upon the number of solute particles, not upon their identity
Dilute solution
A solute that contains a relatively small amount of solute
Concentrated solution
A solution that contains a large amount of solute
Unsaturated solution
A solution that contains less solute than a saturated solution at a given temperature and pressure; if additional solute is added to an unsaturated solution, the solute will dissolve until the solution is saturated
Supersaturated solution
A solution that contains more solute than it can theoretically hold at a given temperature; the crystallization of a supersaturated solution can be initiated if a very small crystal, called a seed crystal, of the solute is added
Saturated solution
A solution that contains the maximum amount of solute for a given quantity of solvent at a constant temperature and pressure
How is pH used to classify a solution as neutral, acidic, or basic?
A solution with a pH less than 7.0 is acidic. A solution with a pH of 7.0 is neutral. A solution with a pH greater than 7.0 is basic.
Would a strong acid have a large or a small Ka? Explain your answer.
A strong acid is completely disassociated; Ka must be large
How did Arrhenius define an acid and a base?
According to Arrhenius, acids are hydrogen-containing compounds that ionize to yield hydrogen ions (H+) in aqueous solution. Bases are compounds that ionize to yield hydroxide ions (OH-) in aqueous solution.
How did Lewis define an acid and a base?
According to Lewis, an acid accepts a pair of electrons and a base donates a pair of electrons during a reaction.
What distinguishes an acid from a base in the Bronsted-Lowry theory?
According to the Bronsted-Lowry theory, an acid is a hydrogen-ion donor and a base is a hydrogen-ion acceptor.
Write a general word equation for a neutralization reaction.
Acid + base = a salt + water
How are acids and bases classified as either strong or weak?
Acids and bases are classified as strong or weak based on the degree to which they ionize in water.
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.
Big Idea: Reactions
Chemists define acids and bases according to the ions they yield in aqueous solution. Chemists also define acids and bases based on whether they accept or donate hydrogen ions, and whether they are electron-pair donors or acceptors. The pH of a solution reflects the hydrogen-ion concentration. Chemists use acid-base reactions to determine the concentration of an acid or a base in solution.
What are two ways of expressing the ratio of solute to solvent in a solution?
Chemists use two ways to express the ratio of solute particles to solvent particles: in molality and in mole fractions.
What effect does dilution have on the amount of solute?
Diluting a solution reduces the number of moles of solute per unit volume, but the total number of moles of solute in solution does not change.
What are two methods that are used to measure pH?
Either acid-base indicators or pH meters can be used to measure pH.
Explain why a buffered solution cannot absorb an unlimited amount of acid or base.
Eventually the buffer capacity of the buffer is exceeded and the pH will change significantly with the addition of a strong acid or base.
How are [H+] and [OH-] related in an aqueous solution?
For aqueous solutions, the product of the hydrogen-ion concentration and the hydroxide-ion concentration equals 1.0 x 10^-14.
Write an equation showing the self-ionization of water.
H2O = H+ + OH-
Write an equation showing why an aqueous solution of sodium hydrogen carbonate is basic.
HCO3- (aq) + H20 (I) = H2CO3 (aq) + OH- (aq)
How can you describe the equilibrium in a saturated solution?
In a saturated solution, a state of dynamic equilibrium exists between the solution and any undissolved solute, provided that the temperature remains constant.
What products form when an acid and a base react?
In general, acids and bases react to produce a salt and water.
At what point in a titration does neutralization occur?
Neutralization occurs when the number of moles of hydrogen ions is equal to the number of moles of hydroxide ions.
How do percent by volume and percent by mass differ?
Percent by volume of a solution is the ratio of the volume of solute to the volume of solution. - Percent by volume (%(v/v)) = (volume of solute/volume of solution) x 100% Percent by mass of a solution is the ratio of the mass of the solute to the mass of the solution. - Percent by mass (%(m/m)) = (mass of solute/mass of solution) x 100%
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.
When is the solution of a salt acidic or basic?
Salts that produce acidic solutions have positive ions that release hydrogen ions to water. Salts that produce basic solutions have negative ions that attract hydrogen ions from water.
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.
Big Idea: The Mole and Quantifying Matter
Solubility, miscibility, concentration, and colligative properties are used to describe and characterize solutions. Solution concentration can be quantified in terms of molarity (moles of solute per liter of solution), molality (moles of solute per kilogram of solvent), percent by volume, and percent by mass.
What factors affect the solubility of a substance?
Temperature affects the solubility of solid, liquid, and gaseous solutes in a solvent; both temperature and pressure affect the solubility of gaseous solutes.
Explain how the Lewis theory is a more general classification system than either the Arrhenius descriptions or the Bronsted-Lowry theory.
The Lewis theory explains the behavior of compounds that act like bases without accepting hydrogen ions or that act like acids without donating hydrogen.
Solubility
The amount of solute that dissolves in a given quantity of a solvent at a specified temperature and pressure to produce a saturated solution; solubility is often expressed in grams of solute per 100 g of solvent (g/100 g H2O), and sometimes the solubility of a gas is expressed in grams per liter of solution (g/L)
Molal boiling-point elevation constant
The change in boiling point for a 1-molal solution of a nonvolatile molecular solute; Kb
Molal freezing-point depression constant
The change in freezing point for a 1-molal solution of a nonvolatile molecular solute; Kf
Boiling-point elevation
The difference in temperature between the boiling point of a solution and the boiling point of the pure solvent
Freezing-point depression
The difference in temperature between the freezing point of a solution and the freezing point of the pure solvent
What factors affect how fast a substance dissolves?
The factors that affect how fast a substance dissolves include agitation, temperature, and the particle size of the solute.
Why is the pH of pure water at 25 degrees Celsius equal to 7.0?
The hydrogen ion concentration in pure water at 25 degrees Celsius is 1 x 10^-7 M. The negative logarithm or pH of this concentration is 7.0.
How is it possible to recognize the endpoint of a titration?
The indicator changes color.
How are freezing-point depression and boiling-point elevation related to molality?
The magnitudes of the freezing-point depression (Delta Tf) and the boiling-point elevation (Delta Tb) of a solution are directly proportional to the molal concentration (m), assuming the solute is molecular, not ionic.
Molality (m)
The number of moles of solute dissolved in 1 kilogram (1000 grams) of solvent; molality is also known as molal concentration
Molarity (M)
The number of moles of solute dissolved in one liter of solution; Molarity is also known as molar concentration
Mole fraction
The ratio of the moles of that solute to the total number of moles of solvent and solute
Henry's Law
The relationship which states that at a given temperature, the solubility (S) of a gas in a liquid is directly proportional to the pressure (P) of the gas above the liquid. In other words, as the pressure of the gas above the liquid increases, the solubility of the gas increases. Similarly, as the pressure of the gas decreases, the solubility of the gas decreases. Formula: (S1/P1) = (S2/P2) - S1 is the solubility of a gas at one pressure, P1; S2 is the solubility at another pressure, P2.
Name and distinguish between the two components of a solution.
The solvent is the substance in which the solute is dissolved.
Why are Mg(OH)2 and Ca(OH)2 classified as strong bases even though their saturated solutions are only mildly basic?
They have high Kb values. Their concentration in a saturated solution is low because of their low solubility.
What are the three colligative properties of solutions?
Three important colligative properties of solutions are vapor-pressure lowering, freezing-point depression, and boiling-point elevation.
How do you calculate the molarity of a solution?
To calculate the molarity of a solution, divide the number of moles of solute by the volume of the solution in liters. - Molarity (M) = (moles of solute/liters of solution)
Explain why solutions of salts that hydrolyze water do not have a pH of 7.
Weak-acid anions accept protons from water, increasing the pH of the solution. Weak-base cations donate protons to water, decreasing the pH.
Is it possible to have a concentrated weak acid? Explain.
Yes, acids like acetic acid dissolve well but ionize poorly.
How is the pH of a solution calculated?
the negative logarithm of the [H+]