Ka, Kb and Ionization Constant

Acids

100

What is a Bronsted-Lowery acid?

H⁺ donor

200

What is the formula for K_a in terms of [A-],[HA] and [H3O⁺]?

K_a=[H₃O⁺][A^-]/[HA]

300

Is an acid with a very small Ka value a strong acid or a weak acid?

Weak acid

400

What is the K_a value of an acid with the K_b value of 7x10^-15?

K_a+K_b=K_w

K_w=1x10^-14

K_b=7x10^-15

K_a=K_w-K_b

K_a=(1x10^-14)-(7x10^-15)

=3x10^-15

Bases

100

What is a Bronsted-Lowery base?

H⁺ accpetor

200

What is the formula for K_b in terms of [OH^-][BH⁺] and[B]?

K_b=[BH⁺][OH⁻]/[B]

300

Which describes a chemical that would be basic?

A. [H₃O⁺]>1.0x10^-7M

B. [H₃O⁺]=1.0x10^-7M

C. [H₃O⁺]<1.0x10^-7M

C. [H₃O⁺]<1.0x10^-7M

400

What is the value of K_b if pK_b=12.3?

K_b=10^-pKb

K_b=10^-12.3

=5.01x10^-13

Word Problems

100

What is the K_a value if [H₃O⁺]=4.8x10^-3M, [HA]=0.0026M and [A^-]=4.8x10^-3M?

K_a=[H₃O⁺][A^-]/[HA]

=(4.8x10^-3M)(4.8x10^-3M)/(0.0026M)

=8.8x10^-3

200

What is the K_a value if [H₃O⁺]=6.2x10^-3M, [A^-]=1.5x10^-3M and [HA]=0.0079M?

K_a=[H₃O⁺][A^-]/[HA]

=(6.2x10^-3M)(1.5x10^-3)/(0.0079M)

=1.17x10^-3

300

Calculate the K_a for the following equation, given that [H₃O⁺]=4.6x10^-3.Suppose we determine that it is a 0.100 M solution of HA.

HA(aq)+H₂O(l)⇌H₃O⁺(aq)+A⁻(aq)

                  [HA] (M)       [A−] (M)     [H3O+] (M)

(I)                 0.100              0                  0

(C)                  −x              +x                 +x

(E)              0.100−x            x              4.6x10⁻³

[HA]=(0.100−x)M =(0.100−4.6x10⁻³)M

= 0.0954 M

K_a=[H₃O⁺][A^-]/[HA]

=(4.6x10⁻³)(4.6x10⁻³)/(0.0954)

=2.21x10^-4

400

Given the reaction: (CH₃)₃N(aq)+H₂O(𝓁) ⇌ (CH₃)₃NH⁺(aq)+OH⁻(aq). It is a 0.500M solution with a [OH^-]=7.4x10^-3. What is the value of K_b?

        [(CH₃)₃N](M)      [(CH₃)₃NH⁺](M)    [OH^-](M)

(I)         0.500                     0                        0

(C)     -7.4x10^-3                  +7.4x10^-3       +7.4x10^-3

(E)      0.4926                  7.4x10^-3             7.4x10^-3

K_b=  [(CH₃)₃NH⁺][OH^-]/[(CH₃)₃N]

=(7.4x10^-3)(7.4x10^-3)/(0.4926)

=1.11x10^-4

Ionization

100

True or False: Strong acids partially ionize in water.

FALSE: strong acids completely ionize in water.

200

Which of the three acids is the most extensively ionized in a 0.10 M solution of the acid?

A. K_a= 4.5x10^-6

B. K_a=8.2x10^-5

C. K_a=6.7x10^-5

B. K_a=8.2x10^-5

300

Which of the following acids has the lowest % ionization in a 1.00M solution of the acid?

A. K_a=4.0x10^-4

B. K_a=5.6x10^-5

C. K_a=5.9x10^-5

D. K_a=5.5x10^-5

D. K_a=5.5x10^-5

400

Calculate the % ionization of something with the [BH⁺]_equilibrium=3.28x10^-4M and [B]_initial=0.07M.

% ionization=[BH⁺]_equilibrium/[B]_initial x100%

% ionization= 3.28x10^-4M/0.07M x100%

=0.46%

Random

100

True or False: The stronger the acid, the weaker its conjugate base.

TRUE: The stronger the acid, the weaker its conjugate base.

200

Which acid is stronger? Acid A with K_a=7.9x10^-6 or Acid B with K_a=6.1x10^-6.

Acid A 

Because 7.9x10^-6>6.1x10^-6 & the bigger the K_a value, the stronger the acid.

300

What is an Arrhenius acid?

H⁺ releaser

400

What is an Arrhenius base?

OH^- releaser