Chemistry B Unit 2

What is the percent by volume of ethanol (C2H6O) in the final solution when 85 mL of ethanol is diluted to a volume of 250 mL with water?

%(v/v) = (volume of solute)/(volume of solution) * 100% %(v/v) = 85 mL ethanol/250 mL * 100% %(v/v) = 85 ethanol/250 * 100% 34% ethanol (v/v)

How many grams of potassium iodide must be dissolved in 500.0 g of water to produce a 0.060 molal KI solution?

0.060 mol KI / 1.000 kg H2O 166.0 g KI / 1 mol KI 0.5000 kg H20 * 0.060 mol KI / 1.000 kg H2O * 166.0 g KI / 1 mol KI 0.5000 * 0.060 / 1.000 * 166.0 / 1 mol KI = 5.0 g KI

To 225 mL of a 0.80M solution of KI, a student adds enough water to make 1.0 L of a more dilute KI solution. What is the molarity of the new solution?

0.18M

What is the pH of a solution if [OH -] = 4.0*10 ^-11 M?

1*10 ^-14 M / 4.0*10 ^-11 M = 2.5*10 ^-4 M = [H +] pH = - log [2.5 * 10 ^-4] pH = -(-3.60) pH = 3.60

If the [H +] in a solution is 1.0*10 ^-5 M, is the solution acidic basic, or neutral? What is the [OH -] of this solution?

1.0*10 ^-5 M > 1*10 ^-7 M, therefor the solution is acidic 1*10 ^-14 M / 1.0*10 ^-5 M = 1.0*10 ^-9 M = [OH -]

Antifreeze protects a car from freezing. It also protects it from overheating. Calculate the freezing-point depression of a solution containing exactly 100 g of ethylene glycol (C2H6O2) antifreeze in 0.500 kg of water.

100 g C2H6O2 * 1 mol C2H6O2 / 62.0 g C2H6O2 = 1.61 mol C2H6O2 m (molality) = mol solute / kg solvent = 1.61 mol / 0.500 kg = 3.22 m ∆ T(sub)f = K(sub)f * m (molality) = 1.86˚ C/m * 3.22m = 5.99˚C

How many milliliters of alcohol are in 167 mL of an 85.0% (v/v) alcohol solution?

142 mL

How many grams of glucose are needed to make 2000 g of a 2.8% glucose (m/m) solution?

2.8% = (2.8 g glucose)/(100 g solution) 2000 g solution * (2.8 g glucose)/(100 g solution) 2000 * (2.8 g glucose)/(100) 56 g glucose

If the percent by volume is 2.0% and the volume of solution is 250 mL, what is the volume of solute in solution?

5.0 mL

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 neutral. A solution with a pH greater than 7.0 is basic.

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 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 ionise in water.

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 are two methods that are used to measure pH?

Either acid-base indicators of pH meters can be used to measure pH.

What is a hydronium ion?

H3O +, is the ion that forms when a water molecule gains a hydrogen ion

To find the value of K(sub)a of an acid in water what equation must you use and what do the variables mean?

K(sub)a = [H +][A -]/[HA] [HA] is the equilibrium concentrations of the acid [A -] is the anion from the dissociation of the acid [H +] is the hydrogen ion

Example acid dissociation constant equation with ethanoic acid (CH3COOH)

K(sub)eq * [H2O] = K(sub)a = [H3O +] * [CH3COO][CH3COOH]

Example equilibrium-constant equation with ethanoic acid (CH3COOH)

K(sub)eq = [H3O +] * [CH3COO -][CH3COOH] * [H2O]

One saline solution contains 0.90g NaCl in exactly 100 mL of solution. What is the molarity of the solution?

M = (0.90g NaCl)/(100 mL) * (1 mol NaCl)/(58.5g NaCl) * (100 mL)/(1 L) M = (0.90)/(100) * (1 mol NaCl)/(58.5) * (100)/(1 L) M = 0.15 mol/L =0.15M

What is the equation that shows the relationship between molarity and volume of two solutions?

M1 * V1 = M2 * V2

How many mililiters of aqueous 2.00 M MgSO4 solution must be diluted with water to prepare 100.0 mL of aqueous 0.400 M MgSO4?

M1*V1=M2*V2 V1 = M2*V2/M1 V1 = (0.400M * 100.0 mL)/2.00M V1 = (0.400 * 100.0 mL)/2.00 V1 = 20.0 mL

percent by mass volume formula

Percent by volume (%(m/m)) = (mass of solute)/(mass of solution) * 100%

percent by volume formula

Percent by volume (%(v/v)) = (volume of solute)/(volume of solution) * 100%

How are freezing-point depression and boiling-point elevation related to molality?

The magnitudes of the freezing point depression and the boiling point elevation of a solution are directly proportional to the molal concentration (m), assuming the solute is molecular, not ionic.

neutral solution

any aqueous solution in which [H +] and [OH -] are equal

Henry's law

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 S1/P1 = S2/P2

A solute depresses the freezing point because the solute ______________. a. is colder than the solvent b. disrupts crystal formation of the solvent c. tends to sink to the bottom of the solution d. has bigger molecules than the solvent

b.

In a concentrated solution there is ____. a. no solvent b. a large amount of solute c. a small amount of solute d. no solute

b.

Which of the following is NOT a colligative property of a solution? a. boiling point elevation b. supersaturation c. vapour pressure lowering d. freezing point depression

b.

Which of the following operations yields the number of moles of solute? a. molarity * moles of solution b. molarity * liters of solution c. molarity * mass of solution d. moles of solutions / volume of solution

b.

What is boiling-point elevation?

because adding a nonvolatile solute lowers the vapour-pressure of a solution, it takes more kinetic energy to raise the vapour pressure of the liquid, therefor, the boiling point is higher. The difference in temperature between the boiling point of a solution and the boiling point of the pure solvent is the boiling-point elevation

How does pressure affect solubility?

changes in pressure have little effect on the solubility of solids in liquids. gas solubility increases as the partial pressure of the gas above the solution increases

supersaturated solution

contains more solute than it can theoretically hold at a given temperature

If a cyrstal added to an aqueous solution causes many particles to come out of the solution, the original solution was ________. a. unsaturated b. saturated c. an emulsion d. superstaturated

d.

In which of the following is the solution concentration expressed in terms of molarity? a. 10g of solute / 1000 g of solution b. 10g of solute / 1000 mL of solution c. 10 mL of solute / 1 L of solution d. 10 mol of solute / 1 L of solution

d.

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 the solution does not change

How does agitation affect dissolving?

dissolving occurs at the surface of solute, agitation (stirring or shaking) continuously brings fresh solvent into contact with the solute; this speeds of dissolving

How are [H+] and [OH-] related in an aqueous solution?

for aqueous solutions, the product of the hydrogen-ion concentratoin and the hydroxide-ion concentration equals 1.0 x 10 ^-14

Identify the units usually used to express the solubility of a solute.

grams of solute per 100g of solvent (g/100g); grams per liter of solution (g/L)

Arrhenius' list of six common acids

hydrochloric acid (HCl), nitric acid (HNO3), sulfuric acid (H2SO4), phosphoric acid (H3 PO4), ethanoic acid (CH3COOH), carbonic acid (H2CO3)

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

How can concentration by expressed quantitatively?

in molarity

immiscible

liquids that are insoluble in one another

What are three ways to calculate the concentration of a solution?

molarity, percent by volume, percent by mass

What does NOT change when a solution is diluted by the addition of solvent?

number of moles of solute

How to calculate the pH.

pH = - log [H +]

The pH of an unknown solution is 6.35. What is the hydrogen-ion concentration of the solution?

pH = - log [H +] 6.35 = - log [H +] log[H +] = -6.35 [H +] = antilog(-6.35) [H +] = 4.5 * 10 ^-7 M

What is the pH of a solution with a hydrogen-ion concentration of 4.2 * 10 ^-10 ?

pH = - log [H +] pH = - log [4.2 * 10 ^-10] pH = -(-9.38) pH = 9.38

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, whereas percent by mass is the ratio of the mass of the solute to the mass of the solution

Examine the factors that determine the mass of a solute that will dissolve in a given mass of solvent.

temperature affects the solubility of a solid solutes in a solvent; both temperature and pressure affect the solubility of gaseous solutes in a solvent. This means that temperature and pressure affect how much of a solute will dissolve in a solvent.

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

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

How does temperature affect dissolving?

the increase of kinetic energy causes the particles of the solvent to collide with the particles of the solute, this causes the solute to break apart and dissolve faster

molality (m)

the number of moles of solute dissolved in 1 kilogram (1000 grams) of solvent; known as molal concentration Molality (m) = moles of solute / kilogram of solvent

molarity (M)

the number of moles of solute dissolved in one liter of solution; molar concentration

ion-product constant for water (K(sub)w)

the product of the concentrations of the hydrogen ions and hydroxide ions K(sub)w = [H +] * [OH -] = 1.0 * 10 ^-14

base dissociation constant (K(sub)b)

the ratio of the concentration fo the conjugate acid times the concentration of the hydroxide ion to the concentration of the base

acid dissociation constant (K(sub)a)

the ratio of the concentration of the dissociated form of an acid to the concentration of the undissociated form

mole fraction

the ratio of the moles of the solute to the total number of moles of solvent and solute

How does particle size of the solute affect dissolving?

the smaller the particles are, the more surface area of the solute will be exposed to the solvent; this causes the solute to dissolve faster

How does temperature affect solubility?

the solubility of most solid substances increases as the temperature of the solvent increases; some solid substances decrease in solubility as the temperature of the solvent increases. the solubility of most gases are greater in cold water than in hot

How do you calculate molarity of a solution?

to calculate the molarity of a solution, divide the number of moles of the solute by the volume of the solution in liters Molarity (M) = moles of solute / liters of solution

What are three colligative properties of solutions?

vapour-pressure lowering, freezing-point depression, and boiling point elevation

What is freezing-point depression?

when a substance freezes, its particles take on an orderly pattern, the presence of a solute disrupts this pattern because of the shells of water of solvation, as a result, more kinetic energy must be withdrawn from a solution than a pure solvent to solidify; the difference in temperature between the freezing point of a solution and the freezing point of the pure solvent is called the freezing-point depression

When do you use the percent by volume to find the concentration?

when both the solute and the solvent are liquids

What is self-ionisation of water?

when the collision between water molecules are energetic enough to cause a hydrogen ion to transfer from one water molecule to another. The two water molecules become (H3O +) and (OH -) H20 <-> H+(aq) + OH-(aq)

miscible

when two liquids dissolve in each other in all proportions; the liquid that is present in the larger amount is considered the solvent

What is the boiling point of a 1.50m NaCl solution?

∆T(sub)b = K(sub)b * m = 0.512˚C/m * 3.00m = 1.54˚C T(sub)b = 100˚C + 1.54˚C

What happens to the solubility of a gas, in a liquid, if the partial pressure of the gas above the liquid decreases? a. the solubility decreases b. the solubility increases c. the solubility remains the same d. the solubility cannot be determined

a.

Which of the following expressions is generally used for solubility? a. grams of solute per 100 grams of solvent b. grams of solvent for 100 mililiters of solute c. grams of solute per 100 grams of solution d. grams of solute per 100 mililiters of solution

a.

Which of the following pairs of factors affects the solubility of a particular substance? a. temperature and the nature of solute and solvent b. temperature and degree of mixing c. particle size and degree of mixing d. particle size and temperature

a.

Which of the following usually makes a substance dissolve faster in a solvent? a. agitating the solution b. increasing the particle size fo the solute c. lowering the temperature d. decreasing the number of particles

a.

What factors affect how fast a substance dissolves?

agitation, temperature, particle size of teh solute

weak acid

an acid ionises only slightly in aqueous solution

strong acid

an acid that is completely ionised in aqueous solution

True or false: the greater the K(sub)a value the stronger the acid.

True

Ethylene glycol (EG, or C2H6O2) is added to automobile cooling systems to protect against cold weather. What is the mole fraction of each component in a solution containing 1.25 mol of ethylene glycol and 4.00 mol of water?

X(sub)EG = n(sub)EG / n(sub)EG + n(sub)H2O X(sub)H20 = n(sub)H2O / n(sub)EG + n(sub)H2O X(sub)EG = 1.25 mol / 1.25 mol + 4.00 mol = 0.238 X(sub)H20 = 4.00 mol / 1.25 mol + 4.00 mol = 0.762

In a 0.1000M solution of ethanoic acid, [H +] = 1.34 * 10 ^-3M. Calculate K(sub)a of the this acid. Refer to Table 19.7 for the ionisation equation for the ethanoic acid.

[H +] = [CH2COO -] = 1.34 * 10 ^-3M (0.1000 - 0.00134)M = 0.0987M K(sub)a = ([H +] * [CH3COO -]) / [CH3COOH] =((1.34 * 10 ^-3) * (1.34 * 10 ^-3)) / 0.0987 =1.82 * 10 ^-5

strong base

a base that dissociates completely into metal ions and hydroxide ions in an aqueous solution

weak base

a base that reacts with water for form the conjugate acid of the base and hydroxide ions

molal boiling-point elevation constant (K(sub)b)

a constant that is equal to the change in boiling point for a 1-molal solution of a nonvolatile molecular solute T(sub)b = K(sub)b * m (molality)

molal freezing-point depression constant (K(sub)f)

a constant that is equal to the change in freezing point for a 1-molal solution of a nonvolatile molecular solute T(sub)f = K(sub)f * m (molality)

concentration of a solution

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

acidic solution

a solution in which [H +] is greater than [OH -] [H +] is greater than 1*10 ^-7 M

basic solution

a solution in which [H +] is one less than [OH -] [H +] is less than 1*10 ^-7 M

concentrated solution

a solution that contains a large amount of solute

dilute solution

a solution that contains a relatively small amount of solute

What is vapour-pressure lowering?

a solution that contains a solute that is nonvolatile (not easily vapourised) always has a lower vapour pressure than the pure solvent; in an aqueous solution, within the liquid and at the surface, ions are surrounded by layers of associated water molecules, or shells of water of solvation, the formation of these shells decreases number of solvent molecules that have enough kinetic energy to escape as vapour. Ionic solutes that dissociate have greater effects on vapour pressure, because the vapour pressure is affected by the number of particles and the ions in ionic compounds split up when dissolved

unsaturated solution

a solution that contains less solute that a saturated solution at a given temperature and pressure

saturated solution

a solution that contains the maximum amount of solute for a given quantity of solvent at a constant temperature and pressure