# Chem

posted by .

Methylaime, CH3NH2.
If a 0.100 mol/L solution of methyamine has a pH of 11.80, calculate the ionization constant for the weak base. What is an ionization constant. Is it just K?

This is what I did so far:

11.80 = -log (concentration of h3o+)
10^-11.80 = (concentration of h3o+)
1.58 x 10^.12 = (concentration of h3o+)

K = (1.58 x 10^-12)^2 / (0.1-1.58 x 10^-12)

Not too sure what to do from here :S

• Chem -

Think NH3 and yes, Ka is the ionization constant.
You know what to do with NH3.
NH3 + HOH ==> NH4^+ + OH^- so in an analogous fashion,
CH3NH2 (this is just NH3 with a CH3 in place of one of the H atoms. These are bases, too, and react the same way.
CH3NH2 + HOH ==> CH3NH3^+ + OH^-
So use an ICE chart to determine OH^-, CH3NH3^+ and CH3NH2 and calculate Ka.
I am getting something like 4 x 10^-4. Look up Kb for CH3NH2 in your text tables to see what it should be.

• Chem -

I don't understand how to figure out the equation. I thought it would be this:
CH3NH2 + HOH ==> CH3NH+ + H30

:S How do I know what the products will be?

• Chem -

You KNOW
NH3 + HOH ==> NH4^+ + OH^-. You KNOE NH3 is a weak base but it is a stronger base than H2O, therefore, the H^+ is pulled from the HOH to form NH4^+.
Amines are just substituted ammonia and there are number of them. When you see NH2 it is RNH2 or RNH or R3N so we are talking about three classes of amines where R may vary. In this case we have
CH3NH2 where CH3 is the R group added. And RNH2 + HOH ==> RNH3^+ + OH^-/
The reaction is strictly analogous to NH3. Do accordingly.

• Chem -

I understand now. Thank you :)

## Similar Questions

1. ### Stupid Chemistry

Ok, blonde moment here, Kb is the same as Ka but just for bases and Ka is for acids correct?
2. ### biochemistry

A weak base has pKb = 9.25.. A. Calculate the % ionization at pH = 8.25 B. Calculate the % ionization at pH = 10.25 C. What is the pH when 50% of the weak base is ionized?
3. ### chemistry

For a week acid whose ionization constant is 1.75 x 10(-5), the pH of its solution is 3.0. Determine its degree of ionization and its percent ionization.
4. ### CHEMISTRY

calculate the ionization constant of the conjugate base for a solution made from 0.2Molar HC2H3O2 and 0.5Molar C2H3O2.The ionization constant for the acid (HC2H3O2) IS 1.8 Multiplied by 10^(-5)
5. ### chemistry

What is the pH of a buffer solution made from 0.20M HC2H3O2 abd 0.5M C2H302^-.The ionization constant of the acid (Ka)(HC2H3O2)is 1.8multiplied by 10^-5. (ii)Calculate the ionization constant of its conjugate base
6. ### Chemistry

Provide equations for each of the following: a. Dissociation of a strong base in water solution b. Ionization of a strong acid in water solution: c. Ionization of a weak acid in water solution: d. Ionization of a weak base in water …
7. ### Chemistry

Aniline, C6H5NH2, is a weak base. If the hydroxide ion concentration of a 0.223 M solution is 9.7 10-6 M, what is the ionization constant for the base?
8. ### Chemistry

Aniline, C6H5NH2, is a weak base. If the hydroxide ion concentration of a 0.201 M solution is 9.2 10-6 M, what is the ionization constant for the base?
9. ### Chem

What simplifying assumptions do we usually make in working problems involving equilibria of salts of polyprotic acids?
10. ### Chemistry

Pyridine, a substance used as a catalyst in some synthetic reactions is a very weak base its degree of ionization is equal to 0.03% in solution 0.02 mol L -ยน. Determine the ionization constant.

More Similar Questions