21. The pH of a 0.120 M phenol solution is (Ka of phenol = 1.3 x 10-10): a. 1.00

Question

21. The pH of a 0.120 M phenol solution is (Ka of phenol = 1.3 x 10-10):

a. 1.000

b. 10.81

c. 11.11

d. 5.40

e. 4.48

22. Which list gives equal concentrations of the following solutions in order of decreasing acidity?

HC3H5O3 (Ka = 1.4 x 10-4)       H2O (Ka = 1.0 x 10-14)              HOCl (Ka = 3.5 x 10-8)

HCN (Ka = 4.9 x 10-10)                HCl (Ka = 2 x 106)

a. HC3H5O3 > HCl > HOCl > HCN > H2O

b. HCl > HC3H5O3 > HOCl > HCN > H2O

c. HCN > HOCl > HCl > HC3H5O3 > H2O

d. HCl > HC3H5O3 > HOCl > H2O > HCN

e. H2O > HCN > HOCl > HC3H5O3 > HCl

23. Which statement is true?

a. As the strength of a weak acid increases, the percent dissociation decreases

b. As the concentration of a weak acid increases, the percent dissociation increases.

c. As the strength of a weak acid decreases, the percent dissociation increases.

d. The percent dissociation of a weak acid is independent of the identity of the weak    

      acid.

e. As the value of Ka increases, the percent dissociation increases.

25. Which of the following salts will form a basic solution?

NaBr

Ca(NO3)2

NH4Cl

NaCH3CO2

Al(ClO4)3

Explanation / Answer

Answer – 21) We are given, [C6H5OH] = 0.120 M , Ka = 1.30*10-10

We need to put ICE chart -

C6H5OH + H2O ------> H3O+ + C6H5O-

I 0.120                          0           0

C -x                              +x          +x

E 0.120-x                      +x          +x

Ka = [H3O+] [C6H5O-] / [C6H5OH]

1.30*10-10 = x*x /(0.120-x)

1.30*10-10 *(0.120-x) = x2

We can neglect x in the 0.120-x , since 5% rule

2.15*10-6 = x2

x = 3.95*10-6 M

so, x = [H3O+] = 3.95*10-6 M

so, pH = -log [H3O+]

           = -log 3.95*10-6 M

           = 5.40

So answer for this question is d) 5.40

22) When we are given equal concentrations of the following solutions in order of decreasing acidity. We know as the Ka value decreasing the acidity decreasing, so list of order of decreasing acidity as follow –

b. HCl > HC3H5O3 > HOCl > HCN > H2O

23) In this one we are given statements and we need to choose the correct one.

a statement is false, since as the strength of a weak acid increases, the percent dissociation increase not decreasing.

b statement is false, since as the strength of a weak acid increases, the percent dissociation increases not concentration increase

c statement is false, since as the strength of a weak acid increase not decreases, the percent dissociation increases.

d statement is also false, since as the percent dissociation of a weak acid is dependent of the identity of the weak acid.

e statement is true, as the value of Ka increases, the percent dissociation increases.

25 ) We know the salt when soluble and form the strong base then that salt is form a basic solution

NaBr + H2O ----> NaOH + HBr  

In this one both are strong acid and strong base, so this form neutral solution.

Ca(NO3)2 + H2O ----> Ca(OH)2 + 2HNO3  

In this one both are strong acid and strong base, so this form neutral solution.

NaCH3COO + H2O ----> NaOH + CH3COOH  

In this one there is weak acid and strong base, so this form basic solution.

Al(ClO4)3 + H2O ----> Al(OH)3 + 3 HClO4

In this one there is strong acid and weak base, so this form basic solution.

So answer for this one is - NaCH3CO2

Related Questions

Navigate

• Browse (All)
• Browse 2
• Subjects

Integrity-first tutoring: explanations and feedback only — we do not complete graded work. Learn more.