CHE102 Week7

The equivalent point of titration has:

• pH=7

• pH=1

• pH=14

• different pH values for different acids and bases

CN^- and HCN are

• pH<7

• pH>7

• pH=7

• Not predictable

Citric acid has pK₁=3.12, pK₂=4.77

Phosphoric acid has pK₁=2.15, pK₂=7.20, pK₃=12.37

We see that: pK_{1 citric}>pK_{1 phosphoric}, pK_{2 citric}<pK_{2 phosphoric}. But phosphoric acid is the triprotic and citric acid is a diprotic

QUESTION: Which acid has a stronger acidity when they have the same concentration?

• Citric

• Phosphoric

• Not predictable

Stronger acid has ...

• Lower pK_a

• Higher pK_a

• Lower K_a

• Lower pK_b

[different question, not duplicate, two correct answers]

A stronger acid has the conjugate base...

• Higher K_b

• Lower pK_b

• Higher pK_b

• Lower K_b

The pH of region 2. seems "unchanged". The name of this solution is

Carbon dioxide (CO₂) does not directly contribute to acid rain. Acid rain is primarily caused by emissions of sulfur dioxide (SO₂) and nitrogen oxides (NOx). Why?

• H₂CO₃ is a weak acid

• H₂CO₃ is a strong acid

• Acids of SO₂ and NOx are extremely weak

• Acids of SO₂ and NOx are "not too weak" acids.

What is "characteristics" of the analyte in this titration?

• acid

• base

• diprotic (two jumps)

• triprotic (two jumps, but the range 25mL-30mL seems like "a buffer")

Two friends did the same question with different ways. The red one is clearly incorrect (he/she did not check the Q/K ratio to determine the shift to right or left).

HOWEVER, can the red one get the correct answer based on analysis the result?

• No.

• Yes, if he/she makes sure all the concentrations are positive at equilibrium (even that he/she got the negative x).