Question

1) A certain weak acid, HA, has a Ka value of 4.6×10⁻⁷.

Part A

Calculate the percent ionization of HA in a 0.10 M solution.

Express your answer to two significant figures and include the appropriate units.

1.12×10−2 M Ba(OH)2 Express your answer using three significant figures. Enter your answers numerically separated by a comma.

Part B

Calculate the percent ionization of HA in a 0.010 M solution.

Express your answer to two significant figures, and include the appropriate units.

2)

A 0.120 M solution of a weak acid (HA) has a pHof 3.31.

Calculate the acid ionization constant (Ka) for the acid.

Express your answer using two significant figures.

3)

Ammonia, NH3, is a weak base with a Kb value of 1.8×10−5.

Part A

What is the pH of a 8.00×10⁻²M ammonia solution?

Express your answer numerically to two decimal places.

Part B

What is the percent ionization of ammonia at this concentration?

Express your answer with the appropriate units.

4)

If Kb for NX3 is 8.5×10⁻⁶ , what is the the pKa for the following reaction?

HNX3+(aq)+H2O(l)⇌NX3(aq)+H3O+(aq)

Answer 1

Let a be the dissociation of the weak acid
HA <---> H + + A-
initial conc. c 0 0
change -ca +ca +ca
Equb. conc. c(1-a) ca ca

Dissociation constant , Ka = ca x ca / ( c(1-a)
= c a2 / (1-a)
In the case of weak acids a is very small so 1-a is taken as 1
So Ka = ca2
==> a = √ ( Ka / c )
Given Ka = 4.6x10-7
c = concentration = 0.10M
Plug the values we get a = 2.144x10-3
∴ % dissociation = 2.144x10-3 x 100 = 2.144x10-1

Do The remaining in The same manner
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Let α be the dissociation of the weak base
BOH <---> B + + OH-
initial conc. c 0 0
change -cα +cα +cα
Equb. conc. c(1-α) cα cα

Dissociation constant, Kb = (cα x cα) / ( c(1-α)   
= c α2 / (1-α)
In the case of weak bases α is very small so 1-α is taken as 1
So Kb = cα2
==> α = √ ( Kb / c )
Given Kb = 1.8x10-5
c = concentration = 0.08 M
Plug the values we get α = 0.015
So the concentration of [OH-] = cα
= 0.08x0.015
= 1.2x10-3M
pOH = - log [OH-]
= - log (1.2x 10-3)
= 2.9
So pH = 14 - pOH

= 14-2.9

=11.1

Similarly do The remaining