Final Exam: Chem 2

Calculate the pOH of a solution that contains 3.9 x 10-4 M H3O+ at 25°C.

-Log(3.9*10^-4)=3.42 pOH = pH(14) - 3.42 = 10.59

Ammonia, NH3 , is a weak base with a Kb value of 1.8×10−5 . What is the pH of a 0.180 M ammonia solution? Express your answer numerically to two decimal places.

-log (1.8 * 10^5) = 4.74 (1/2 * 4.74) - (1/2)log(0.180) = 2.742 14 - 2.742 = 11.26 pH

pOH is defined as

-log[OH-]

Which of the following solutions could be classified as a buffer?

0.100 M HNO2 and 0.100 M NaNO2

Which of the following solutions could be classified as a buffer? 0.100 M HCl and 0.100 M NaOH 0.100 M HCl and 0.100 M NH4Cl 0.100 M HBr and 0.100 M KBr 0.100 M HNO2 and 0.100 M NaNO2

0.100 M HNO2 and 0.100 M NaNO2

What is the mole fraction of Ar in a sample with 12.4 grams Ar, 35.0 g N2, and 2.91 g He?

0.136

A 25.00-mL sample of 0.175 M HCl is being titrated with 0.250 M NaOH. What is the pH when 0 mL of NaOH has been added?

0.757

Which expression is equivalent to 0.955 m KBr?

0.955 mol KBr/ 1 kg solvent

A 25.00-mL sample of 0.175 M HCl is being titrated with 0.250 M NaOH. What is the pH after 5.00 mL of NaOH has been added?

0.983

What is the molar solubility of AgCl if the Ksp is 1.8 × 10-10? AgCl(s) ⇌ Ag+(aq) + Cl−(aq)

1.3 × 10-5 M

A solution has [Ag+] of 3.2 × 10-3 M and 0.125 M NH3. What is the concentration of Ag+ after the solution reaches equilibrium? Kf of Ag(NH3)2+ = 1.7 × 107

1.3 × 10-8 M

A 25.00-mL sample of 0.175 M HCl is being titrated with 0.250 M NaOH. What is the pH after 11.50 mL of NaOH has been added?

1.386

A 20.00-mL sample of 0.150 M NH3 is being titrated with 0.200 M HCl. What is the pH after 20.00 mL of HCl has been added? Kb of NH3 = 1.8 × 10−5

1.602

What concentration of hydroxide is needed to begin formation of Pb(OH)2 in a solution with a [Pb2+] of 4.5 × 10-5 M? Kf of Pb(OH)2 = 8.0 × 1013

1.7 × 10-5 M

You will complete this step by adding electrons to one side of the equation. 10 H+(aq) + NO3−(aq)→ NH4+(aq) + 3 H2O(l)

10 H+(aq) + NO3−(aq) + 8 e− → NH4+(aq) + 3 H2O(l)

What is the pH of a buffer system that has 0.87 M (CH3)2NH and 0.68 M (CH3)2NH2+? The Kb of methylamine is 5.9 × 10−4.

10.88

A 30.00-mL sample of 0.125 M HCOOH is being titrated with 0.175 M NaOH. What is the pH after 23.0 mL of NaOH has been added? Ka of HCOOH = 1.8 × 10−4

11.723

Determine the pOH of a 0.00598 M HClO4 solution.

11.777 [H+] = [HClO4] = 0.00598M pH = -log[H+] = -log(0.00598) = 2.223 pOH = 14 - 2.223 = 11.77

What is the volume/volume percent of a solution prepared from 10.0 g ethanol in 95.0 g water? The density of ethanol is 0.789 g/mL, and the density of water is 1.00 g/mL.

11.8% (v/v) ethanol

What is the coefficient for H2O(l) when NH3(g) + NO2(g) → N2(g) is balanced in acidic aqueous solution?

12

What is the coefficient for H2O(l) when NH3(g) + NO2(g) → N2(g) is balanced in basic aqueous solution?

12

Which expression is equivalent to 12.4% (m/m) NaCl?

12.4 g NaCl / 100 g solution

A 25.00-mL sample of 0.175 M HCl is being titrated with 0.250 M NaOH. What is the pH after 25.00 mL of NaOH has been added?

12.573

What is the mass/volume percent of a solution prepared from 19.5 g NaOH in 125 g solution? The density of the solution is 1.05 g/mL.

16.4% (m/v) NaOH

What is the mass percent of a solution prepared from 17.5 g MgCl2 in 85.0 g H2O?

17.1% (m/m) MgCl2

What is the mass/volume (m/v) percent of a solution containing 45 g of lithium hydroxide, LiOH, dissolved in enough water, H2O, to make a 250 mL solution?

18% (m/v) LiOH

What is the coefficient for OH−(aq) when SO42−(aq)+ Br2(l) → S2O32−(aq) + BrO3−(aq) is balanced in basic aqueous solution?

2

What is the overall reaction for the following half-reactions? Reduction half-reaction: Ag+(aq) + e− → Ag(s) Oxidation half-reaction: Ni(s) → Ni2+(aq)+ 2 e−

2 Ag+(aq) + Ni(s) → 2 Ag(s) + Ni2+(aq)

What mass of NaF must be added to create 250.0 mL of a buffer solution with a pH = 3.45 and an HF concentration of 0.100 M? The pKa of hydrofluoric acid is 3.16.

2.0 g

What is the osmotic pressure of a 0.850 M solution of glucose in water at 35 °C?

21.5 atm

How many electrons are needed to balance each of the following half-reactions? Reduction half-reaction: Fe3+(aq) + _e− → Fe(s) Oxidation half-reaction: Al(s) → Al3+(aq)+ _e− Overall reaction: Fe3+(aq) + Al(s) → Fe(s) + Al3+(aq)

3 electrons

A buffer solution has 0.620 M HF and 0.710 M F−. If 0.025 mol of HCl is added to 325 mL of the buffer solution, what is the pH after the addition? The pKa of hydrofluoric acid is 3.16.

3.12

What mass of NaCl is present in 50.0 mL of 6.25% (m/v) NaCl solution?

3.13 g

A solution has a [Ag+] of 0.00175 M. What concentration of chromate is needed before precipitation begins? Ksp of Ag2CrO4 = 1.12 × 10-12

3.66 × 10-7 M

What mass of KBr is present in 0.959 m KBr solution if there are 0.350 kg of solvent?

39.9 g

What is the coefficient for H2O(l) when PbO2(s) + I2(s) → Pb2+(aq) + IO3−(aq) is balanced in acidic aqueous solution?

4

What is the coefficient for OH−(aq) when SO32−(aq) + MnO4−(aq) → SO42−(aq) + Mn2+(aq) is balanced in basic aqueous solution?

4

At this point, you need to begin balancing hydrogen atoms by adding hydrogen ions (H+) to one side of the equation. NO3−(aq) → NO(g) + 2 H2O(l)

4 H+ + NO3− → NO + 2 H2O

What is the molality of a solution prepared from 5.25 g LiF and 45.0 g H2O?

4.49 m LiF

1.0 L of a buffer is prepared. It contains 0.125 M HA ( pKa = 4.74) and 0.115 M A− . What is the pH of this buffer after 0.0100 mol of strong acid is added?

4.63

A 40.00 mL sample of 0.10 M weak acid with Ka of 1.8×10−5 is titrated with a 0.10 M strong base. What is the pH after 20.00 mL of base has been added?

4.74

What is the pH of a buffer system that has 0.11 M CH3COOH and 0.15 M CH3COO−? The pKa of acetic acid is 4.75.

4.88

The enthalpy of fusion of solid sodium is 2.60 kJ/mol. Calculate the energy required to melt 43.6 g of solid sodium.

4.94 kJ

What is the coefficient for OH−(aq) when Sn2+(aq) + IO3−(aq) → Sn4+(aq) + I−(aq) is balanced in basic aqueous solution?

6

A buffer solution has 0.750 M H2CO3 and 0.650 M HCO3−. If 0.020 mol of NaOH is added to 275 mL of the buffer solution, what is the pH after the addition? The pKa of carbonic acid is 6.37.

6.40

A solution this basic has pOH< ___?

7

What is the coefficient for H2O(l) when H2O2(aq) + Cr2O72−(aq) → O2(g) + Cr3+(aq) is balanced in acidic aqueous solution?

7

A 25.00-mL sample of 0.175 M HCl is being titrated with 0.250 M NaOH. What is the pH after 17.50 mL of NaOH has been added?

7.000

The vapor pressure of dichloromethane at 260 K is 71 torr. What is the vapor pressure at 310 K, given that ΔHvap = 31.4 kJ/mol?

737 torr

What is the coefficient for OH−(aq) when PbO2(s) + I2(s) → Pb2+(aq) + IO3−(aq) is balanced in basic aqueous solution?

8

The molar solubility of Ag2S is 1.26 × 10-16 M in pure water. Calculate the Ksp for Ag2S.

8.0 * 10^-48 1 mole of Ag2S forms 2 mole of Ag+ therefore, [Ag+]=2x[AgS] = 2X of Ag2S = 2S Ksp= (2S)^2 x S = 4S^3 = 4(1.26 * 10^-16)^3 = 8.0 * 10^-48

A 30.00-mL sample of 0.125 M HCOOH is being titrated with 0.175 M NaOH. What is the pH after 21.4 mL of NaOH has been added? Ka of HCOOH = 1.8 × 10−4

8.30

What is the boiling point of 0.500 m I2 in cyclohexane (normal boiling point = 80.74 °C)? Kb,cyclohexane = 2.79 °C/m

82.14 °C

A buffer solution has 0.625 M HCN and 0.575 M CN−. If 0.030 mol of HCl is added to 400. mL of the buffer solution, what is the pH after the addition? The pKa of hydrocyanic acid is 9.23.

9.08

Calculate the molar solubility of magnesium fluoride (MgF2) in a solution that is 0.750 M in NaF . For magnesium fluoride, Ksp=5.16×10−11 .

9.17×10−11M

What is the pH of a buffer system that has 0.58 M NH3 and 0.41 M NH4+? The Kb of ammonia is 1.8 × 10−5.

9.41

What is a conjugate acid-base pair?

A conjugate acid-base pair are two substances related to each other by the transfer of a proton.

A solution that is ____ has pOH>___?

Acidic, 7

Ammonia, NH3NH3, is a weak base with a KbKb value of 1.8×10−51.8×10−5 What is the pH of a 0.180 MM ammonia solution? What is the percent ionization of ammonia at this concentration?

As initial Concentration of ammonia , NH3 = c = 0.485 M Reaction of NH3 with H2O : NH3 + H2O <----> NH4+ + OH- initial 0.485 0 0 change - x +x +x equilibrium 0.485 - x x x Now , Kb = [NH4+] [OH-] / [NH3] 1.8 × 10-5 = x2 / ( 0.485 - x ) As x is very small , so , 0.485 - x = 0.485 1.8 × 10-5 × 0.485 = x2 x2 = 8.73 × 10-6 x = 0.002954 So , [NH4+] = 0.002954 M Therefore , Percent ionization = ( Equilibrium Concentration of NH4+ / Initial Concentration of NH3 ) × 100 = ( [NH4+] / c ) × 100 = ( 0.002954 M / 0.485 M ) × 100 = 0.61 %

true statement regarding vapor pressure.

As the temperature of a sample increases, the vapor pressure increases.

Which substance is nonpolar?

C4H10 (butane)

Which substance will dissolve in hexane, a nonpolar substance?

CCl4 (carbon tetrachloride, nonpolar)

What is the balanced reduction half-reaction for the unbalanced oxidation-reduction reaction? Na(s) + Cl2(g) → NaCl( s)

Cl2(g) + 2 e− → 2 Cl−(s)

Cr2O72−(aq) → 2 Cr3+(aq) Select the half-reaction that has the correct number of water molecules, on the correct side, in order to balance the reaction. The half-reaction will not be completely balanced.

Cr2O72−(aq) → 2 Cr3+(aq) + 7 H2O(l)

What types of intermolecular forces are found in CH3OCH3?

Dispersion and dipole-dipole forces

Which equation best represents the formation of Fe(CN)63-?

Fe3+(aq) + 6 CN−(aq) ⇌ Fe(CN)63−(aq)

Which of the following substances will dissolve in water, a polar solvent?

Glucose (polar)

What substance is added to balance the hydrogen in a half-reaction?

H+

What substance is added to balance the oxygen in a half-reaction?

H2O

Select the best buffer to maintain a solution at pH = 8.0.

HClO with NaClO, Ka of HClO = 3.5 × 10−8

Which of the following acids is the STRONGEST? The acid is followed by its Ka value. HCOOH, 1.8 × 10-4 HCN, 4.9 × 10-10 HNO2, 4.6 × 10-4 HF, 3.5 × 10-4 HClO2, 1.1 × 10-2

HClO2, 1.1 × 10-2

Which pair of aqueous solutions can create a buffer solution if present in the appropriate concentrations?

HF and NaF

What is the conjugate base of H2PO4- ?

HPO4^2-

substances will dissolve in carbon tetrachloride, a nonpolar solvent?

Hexane (nonpolar)

Find the pH of a 0.250 M aqueous benzoic acid solution. For benzoic acid, Ka=6.5×10−5 .

Ka=[H3O+][A−][HA]=x2(0.250−x)=6.5×10−5 Assume x<<0.250 , x2 / 0.250 = 6.5×10−5 x=4.0×10−3M=[H3O+] % ionization=4.0×10−3M / 0.250M×100%=1.6% , so assumption is valid. pH=−log[H3O+]=−log(4.0×10−3)=2.40

What is the Ksp for the following reaction if the concentration of Fe2+ was measured to be 5.8 × 10-6 M and OH− was measured to be 1.16 × 10-5 M? Fe(OH)2(s) ⇌ Fe2+(aq) + 2 OH−(aq

Ksp = 7.8 × 10-16

Which of the following is the correct solubility product constant for the following reaction? Ca3(PO4)2(s) ⇌ 3 Ca2+(aq) + 2 PO43−(aq)

Ksp = [Ca2+]3[PO43−]2

Which of the following is the correct solubility product constant for the reaction shown below? CaF2(s) ⇌ Ca2+(aq) + 2 F−(aq)

Ksp = [Ca2+][F−]2

Which of the following is the correct solubility product constant for the reaction shown below? Cu3(PO4)2(s) ⇌ 3 Cu2+(aq) + 2 PO43−(aq)

Ksp = [Cu2+]3[PO43−]2

Calculate the molar solubility of barium fluoride (BaF2) . For barium fluoride, Ksp=2.45×10−5 .

Ksp=2.45×10−5=[Ba2+][F−]2=S(2S)2 Solve for S . S=0.0183M

Calculate the molar solubility of magnesium fluoride (MgF2) in a solution that is 0.400 M in NaF . For magnesium fluoride, Ksp=5.16×10−11 .

Ksp=5.16×10−11=[Mg2+][F−]2=S(0.400+2S)2 Make the S is small approximation and solve for [S] . [S]=3.23×10−10M

Select the true statement about the properties of liquids.

Liquids have an indefinite shape and a definite volume.

What is the balanced half-reaction in acidic aqueous solution for MnO4−(aq) → Mn2+(aq)?

MnO4−(aq) + 8 H+(aq) + 5 e−→ Mn2+(aq) + 4 H2O(l)

Which pair of aqueous solutions can create a buffer solution if present in the appropriate concentrations?

NH3 and NH4Cl

An aqueous solution of ammonia is found to be basic. This observation can be explained by the net ionic equation

NH3(aq) + H2O(l) →→ NH4+(aq) + OH-(aq).

Which of the following is a Brønsted-Lowry acid? I2 NH4+ BF3 CI4 NH2-

NH4+

Which pair of aqueous solutions can create a buffer solution if present in the appropriate concentrations?

NaH2PO4 and Na2HPO4

A hydrogen in NH3 will experience hydrogen bonding with _________.

O in H2CO

What type of intermolecular forces are found in CO2?

Only dispersion forces

What equation best represents the behavior of PbSO4 in water?

PbSO4(s) ⇌ Pb2+(aq) + SO42−(aq)

What phase change is known as fusion?

Solid to liquid

What term identifies the phase change from solid to gas?

Sublimation

As the pHpH of a solution increases (gets higher), what happens to the acidity of the solution?

The acidity decreases.

true statement regarding the enthalpy of phase changes.

The enthalpy of vaporization is endothermic.

A solution is buffered at a pH of 6.5, and a small amount of base is added. What happens to the pH of the solution?

The pH will increase a small amount.

What is the triple point?

The point at which all three phases are in equilibrium

Which statement is true about the relationship between intermolecular forces and the boiling point of a liquid?

The stronger the intermolecular forces, the higher the boiling point.

Assume there is a semipermeable membrane separating two compartments: the first compartment contains 3% glucose, and the second compartment is 6% glucose. Select the answer that indicates what molecules will move and the correct direction.

Water (solvent) will move into the second compartment.

What is the pH of a buffer system that has 0.35 M CH3NH2 and 0.42 M CH3NH3+? The Kb of methylamine is 4.4 × 10−4.

YOU WERE SURE AND CORRECT 10.56

Calculate [OH−] in the following aqueous solutions at 25 ∘C. [H3O+]=1.4×10−8 M

[OH−] = 7.1×10−7 M [OH−]===Kw/[H3O+] = 1.0×10−14 / 1.4×10−8 = 7.1×10−7M

Which solution is a buffer? a solution that is 0.100 M in HNO3 and 0.100 M in NaNO3 a solution that is 0.100 M in HNO2 and 0.100 M in NaNO2 a solution that is 0.100 M in HNO2 and 0.100 M in NaCl a solution that is 0.100 M in HNO2 and 0.100 M in HCl

a solution that is 0.100 M in HNO2 and 0.100 M in NaNO2

For the titration of a strong acid with a strong base, the pH at the half-equivalence point volume is _________.

acidic

The titration of HCOOH with NaOH produces a salt and water. The resulting salt is _________.

basic

What type of intermolecular forces are found in BF3?

dispersion forces

A solution this has pOH = 7 is?

neutral

Temporary dipoles occur in _____ molecules, whereas permanent dipoles occur in _____ molecules.

nonpolar; polar

What is the Henderson-Hasselbalch equation?

pH = pKa + log [A-]/[HA] (base/acid)

The enthalpy of freezing is ____________.

the negative of the enthalpy of fusion

Which aqueous solution has the lowest vapor pressure?

χwater = 0.75