Exam #3 (Ch 16 & 17)

Question 1

Strong acid with a strong base

Answer 1

(H3O+) + (OH-) –> 2H2O

Question 2

Weak acid with a strong base

Answer 2

HA + (OH-) –> (A-) + H2O

Question 3

Weak base with a strong acid

Answer 3

(A-) + (H3O+) –> HA + H2O

Question 4

What compounds are soluble? (3)

Answer 4

• (NO3)-
• salts with alkali metals (Na+, Li+, etc)
• most halides (Cl-, F-, etc. NOT Ag+, Pb+2, Hg+2)

Question 5

What compounds are NOT soluble?

Answer 5

• (CO3)-, S-2, OH-; except alkali metals

Question 6

Solubility values can differ due to… (4)

Answer 6

• sometimes solids don’t dissociate completely; ion-pairs, undissociated salt
• sometimes ions react with water
• solubility can be affected by pH
• sometimes complex ions can form

Question 7

What determines the pH before base is added?

Answer 7

Ka and concentration of HA

Question 8

What determines the pH anywhere on the flat part leading up to the equivalence point?

Answer 8

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

Question 9

What determines the pH at the half equivalence point?

Answer 9

pH = pKa

Question 10

What determines the pH at the equivalence point?

Answer 10

Kb and concentration of A-

Question 11

What determines the pH after the equivalence point?

Answer 11

Excess OH- added

Question 12

Entropy (S) increases with… (6)

Answer 12

• more gas molecules
• gas > liquid > solid
• greater molar mass
• greater molecular complexity
• when solids are dissolved
• higher temperature

Question 13

If ΔH < 0 and ΔS > 0, then…

Answer 13

ΔG will be negative (making the reaction spontaneous) at ALL temperatures

Question 14

If ΔH < 0 and ΔS < 0, then ΔG is…

Answer 14

ΔG will be negative (making the reaction spontaneous) at LOW temperatures

Question 15

If ΔH > 0 and ΔS > 0, then ΔG is…

Answer 15

ΔG will be negative (making the reaction spontaneous) at HIGH temperatures

Question 16

If ΔH > 0 and ΔS < 0, then ΔG is…

Answer 16

ΔG will be positive, making the reaction never spontaneous

Question 17

What is ΔG at equilibrium?

Answer 17

0