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CHEM 126 BASIC

ACIDS II

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Question 1

Suppose you have 0.6 M solution of acid HB. Suppose further that Ka >> 1 for this acid. Which of the following statements is true?

Strong and weak acid defined

Select one:


 
Correct

 

Explanation

 Ka = [H+][B-]/[HB]

Strong acids have large Ka and will fully dissociate into ions so the answer should be d as the HB should have fully dissociated

 

Question 2

Suppose you have 0.6 M solution of acid HB. Suppose further that Ka << 1 for this acid. Which of the following statements is true?


Select one:



Correct

 

Explanation

 Weak acids have small Ka and will not fully dissociate so there should be very very little of the ions readily available in the solution 

 

Question 3

Find the pH of 0.15 M CH3COOH. Ka = 1.74 x 10-5M.

Correct

 

Explanation

 acetic acid is a weak acid

Ka = [H+][CH3COO-]/[CH3COOH]

1.74e-5= x^2/(.15)

x=0.0016155

pH=-log(x)= 2.79

 

Question 4

Find the pH of 0.161 M phenol, C6H5OH. The H bonded to the O is acidic, that is,

C6H5OH(aq) + H2O(l) ↔ H3O+(aq) + C6H5O-(aq). Ka = 1.0 x 10-10 M.

Use the same procedure as used in the last problem.

Correct

 

Explanation

 1e-10=x^2/.161

x=0.000004012

pH=-log(x)= 5.3965

 

Question 5

Calculate the approximate [OH-] and [NH4+] in a 0.15 M ammonia solution, NH3(aq).

NH3(aq) + H2O(l) ↔ OH-(aq) + NH4+(aq). Kb = 1.75 x 10-5M.

Use the same procedure as used in the last 2 problems. Details for those who want a little extra help:

Calculate pH of weak base

Correct

 

Explanation

 

 

Question 6

Calculate the pH of 0.029 M ammonia.

NH3(aq) + H2O(l) ↔ OH-(aq) + NH4+(aq) Kb = 1.75 x 10-5


Correct

 

Explanation

1.75e-5 = x^2/0.029

x=0.00071239

pOH= -log(x)=3.1472

14-pOH= 10.85

 

Question 7

Which of the following compounds are Bronsted-Lowry bases?

Bronsted-Lowry acids and bases

Select one or more:
Correct
Correct

Correct Correct Correct

 

Explanation

 

 

Question 8

Determine the conjugate base for the acid HF in ammonia.

HF + NH3 → NH4+ + F-

Select one:


  Correct

 

 

 

Question 9

Indicate whether the ion is acidic, basic, or neutral by writing A, B, or N, respectively.

F- (HF is not one of the 6 strong acids)

 

 

 

Question 10

Cl-       (Is HCl one of the 6 strong acids?)

 

 

 

Question 11

HNO3


 

 

 

Question 12

NO3-


 

 

 

Question 13

CH3COO- (the acetate ion)

 

 

 

Question 14

HCOOH (formic acid)

 

 

 

Question 15

HCOO- (formate ion)

 

 

 

Question 16

Indicate whether the species is acidic, basic, or neutral by writing A, B, or N, respectively.

Ca2+

 

 

 

Question 17

K+


 

 

 

Question 18

CH3NH2 (like NH3 but one of the H is replaced with CH3)

 

 

 

Question 19

CH3NH3+


 

 

 

Question 20

Match strongest to weakest acid.

Ka values

acetic Correct
hydrocyanic Correct
hydrofluoric Correct
iodic Correct
phenol Correct

 

Explanation

 Remember the larger Ka, the stronger the acid.

 

Question 21

Match strongest to weakest conjugate base.


CH3COO- Correct
CN- Correct
F- Correct
IO3- Correct
C6H5O- Correct

 

Explanation

 Remember the weaker the acid, the stronger the conjugate base.

 

Question 22

Which of the following solutions are buffers?

Buffer solutions

Select one or more:
Correct



Correct

 

Explanation

 Remember, to prepare a buffer solution you must use a weak acid and its conjugate base or a weak base and its conjugate acid!

 

Question 23

What is the pKa for phenol? Ka = 1.0 x 10-10.

Buffer calculation

Correct

 

Explanation

 pKa = -log(Ka)= -log(10e-10)


 

Question 24

What is the pH of a buffer solution of phenol and its conjugate base. [C6H5OH] = 0.41 M and [C6H5O]- = 0.78 M.

Correct

 

Explanation

 pH= pKa +log ( CB/A)

=10 + log(.78/.41)

=10.279