Deck 12: Acid-Base Titrations

Question 1

Which statement is FALSE regarding the titration of a weak acid with a strong base? HA + OH⁻ → A⁻ + H₂O

A)At the equivalence point,the pH is due to the hydrolysis of water by the conjugate base,A⁻.
B)Past the equivalence point the pH is due to excess conjugate base,A⁻.
C)Before strong base is added,the pH is due to the ionization of the weak acid,HA.
D)Before the equivalence point,the pH is due to a mixture of HA and A⁻.
E)The pH at the equivalence point is basic.

Answer 1

Past the equivalence point the pH is due to excess conjugate base,A⁻.

Question 2

A 1.000 gram organic sample containing nitrogen is subjected to Kjeldahl analysis.The ammonia gas generated when ammonium is neutralized is distilled into 50.00 mL of 0.1000 M HCl to reform ammonium.If 17.29 mL of 0.1000 NaOH is required to titrate the unreacted HCl,calculate the percent by mass nitrogen in the original sample.

Answer 2

4.58% N

Question 3

For the titration of a strong acid with a strong base,which statement below is FALSE?

A)At V = 0 mL titrant added,the pH is due to initial concentration of strong acid.
B)At the equivalence point,the pH is due to the auto-ionization of water.
C)Between V = 0 mL and the equivalence point,the pH is due to diluted unreacted strong acid.
D)Past the equivalence point,the pH is due to diluted excess strong base.
E)The indicator changes color at the end point due to excess acid.

Answer 3

The indicator changes color at the end point due to excess acid.

Question 4

Which statement is FALSE regarding the titration of a dibasic weak base with a strong acid? B + H⁺ → BH⁺
BH⁺ + H⁺ → BH₂²⁺

A)For V = 0,the pH is dictated by the reaction of B with H₂O.
B)Before the first equivalence point,V_eq1 the buffer created by B and BH⁺ determines the pH.
C)At V_eq1 the pH is due to the reaction of BH⁺ with H₂O.
D)After the first equivalence point,V_eq1 and before the second equivalence point,V_eq2,the buffer created by BH⁺ and BH₂²⁺ determines the pH.
E)At V_eq2 the pH is due to the reaction of BH₂²⁺ with H₂O.

Question 5

A 50.00 mL aliquot of a 0.1000 M propenoic acid solution,H₂CCHCO₂H,is titrated with 0.1250 M NaOH.Calculate the pH when 25.00 mL of NaOH is added.K_a = 5.52 × 10⁻⁵

Question 6

A 25.00 mL aliquot of 0.100 M NH₃ is titrated with 21.00 mL of 0.0900 M HCl.Calculate the pH.K_b = 1.76 x 10⁻⁵

A)5)25
B)8)44
C)8)75
D)5)56
E)7)00

Question 7

Arrange the steps below in the order required to perform a Kjeldahl Nitrogen Analysis.
I Distillation of ammonia into standard hydrochloric acid.
II Neutralize ammonium to release ammonia.
III Digest organic sample with boiling sulfuric acid to convert nitrogen to ammonium.
IV Titrate unreacted standard hydrochloric acid with sodium hydroxide.

A)III,II,I,IV
B)II,I,IV,III
C)I,IV,III,II
D)IV,III,II,I
E)III,I,IV,II

Question 8

Which statement is false regarding the titration of a weak base with a strong acid? B + H⁺ → BH⁺

A)At the equivalence point,the pH is due to the weak acid dissociation of the conjugate acid,BH⁺.
B)Past the equivalence point the pH is due to excess strong acid,H⁺.
C)Before strong acid is added the pH is due to the ionization of the weak base,B.
D)Before the equivalence point,the pH is due to a mixture of B and BH⁺,a buffer.
E)The pH at the equivalence point is acidic.

Question 9

Calculate the pH when 50.00 mL of 0.100 M HNO₃ is titrated with 40.00 mL of 0.0750 M NaOH.

Question 10

The end point for a titration can be determined graphically.The end point volume for a first derivative plot corresponds to:

A)the volume base added where the first derivative curve crosses the x-axis.
B)the volume base added where the first derivative curve has maximum slope.
C)the volume base added where the first derivative curve crosses the y-axis.
D)the volume base added where the first derivative curve has minimum slope.
E)the volume base added where the first derivative curve has a maximum negative slope.

Question 11

A 0.100 M oxalic acid,HO₂CCO₂H,solution is titrated with 0.100 M KOH.Calculate the pH when 25.00 mL of oxalic acid solution is titrated with 35.00 mL of NaOH.K_a1 = 5.4 × 10⁻² and K_a2 = 5.42 × 10⁻⁵ for oxalic acid.

Question 12

A 40.00 mL sample of 0.1000 M diprotic malonic acid is titrated with 0.0900 M KOH.What volume KOH must be added to give a pH of 5.697? K_a1 = 1.42 × 10⁻³ and K_a2 = 2.01 × 10⁻⁶.

A)66.67 mL
B)44.44 mL
C)22.22 mL
D)88.89 mL
E)111.11 mL

Question 13

Strong base solutions require standardization before use because strong bases:

A)precipitate as insoluble metal hydroxides,decreasing the hydroxide concentration.
B)react with atmospheric carbon dioxide to form carbonates,decreasing the hydroxide concentration.
C)react with atmospheric nitrogen to form nitrogen oxides,decreasing the hydroxide concentration.
D)adhere to the inside surface of the solution container,reducing the hydroxide concentration.
E)react with solution impurities to form volatile compounds,increasing the hydroxide concentration.

Question 14

The end point for a titration can be determined graphically.The end point volume for a second derivative plot corresponds to:____________________ .

A)the volume titrant added where the second derivative curve crosses the x-axis.
B)the volume titrant added where the second derivative curve has maximum slope.
C)the volume titrant added where the second derivative curve crosses the y-axis.
D)the volume titrant added where the second derivative curve has minimum slope.
E)the volume titrant added where the second derivative curve has a maximum negative slope.

Question 15

Calculate the pH for the titration of 50.00 mL of a 0.1500 M methylamine with 35.00 mL of 0.1000 M HCl.K_b = 4.42 × 10⁻⁴

Question 16

Which statement is FALSE for indicators?

A)Indicators are acids or bases whose various protonated forms have different colors.
B)The pH range over which an indicator changes color is the transition range
C)Indicators are chosen to change color as close to the end point as possible.
D)The volume difference between the equivalence point and the end point is indicator error.
E)Indicators can change color more than once.

Question 17

A 25.00 mL aliquot of 0.0900 M acetic acid is titrated with a 0.100 M KOH.Calculate the pH when 25.00 mL of base is added.K_a = 1.75 x 10⁻⁵

A)2)30
B)5)27
C)5)71
D)8)73
E)11.70

Question 18

Which statement is TRUE for the leveling effect?
I Acids stronger than water react with water to form hydronium.
II Hydronium is the strongest acid in water.
III In water,strong acids have the same strength.
IV The differences in the strength of strong acids are observed in nonaqueous solvents such as acetic acid.

A)I,III,and IV
B)II and IV
C)II and III
D)II,III,and IV
E)I and III

Question 19

Which statements are TRUE for Gran plots?
I Gran plots are more accurate around end point than first and second derivative plots.
II The end point is determined using concentration/pH data prior to the end point.
III For a constant slope,where the Gran plot crosses the x-axis is the end point volume.
IV Gran plots are used with polyprotic titration curves as well as monoprotic titration curves.

A)I,II,and IV
B)II,III,and IV
C)I,II,and III
D)I,II,III,and IV
E)I,III,and IV

Question 20

Fifty mL of 0.100 M HCl is titrated with 0.1500 M NaOH.The pH at the equivalence point is:

A)1)00.
B)13.18.
C)1)22.
D)12.78.
E)7)00.