[derek0o0]

calculate the pH of:
20ml of 0.5M HCl is added to 40ml 0.25M CH3NH2 (pka 10.6)

so i guess the 1st step is to calculate the mole of each solution
so 20/1000 x 0.5 and 40/1000 x 0.25
= 0.01 mol HCl and 0.01 mol CH3NH2
but what next?

[Borek]

How do these substances react? What will be the product?

[derek0o0]

How do these substances react? What will be the product?

CH3NH2 + HCl => CH3NH3Cl
so..?

[Borek]

CH3NH2 + HCl => CH3NH3Cl

OK, what can you tell about CH₃NH₃⁺?

[Omggg]

if you have the product, then write a chemical balanced equation, then calculate limitent. and then find the Mol for the final one. Find its molarity using the molarity mol equation,

molarity = - ph ^10

use log to solve for PH

not sure if im correct or not, but this is what i would do, only if i was 100% sure about the products.

[AWK]

20ml of 0.5M HCl is added to 40ml 0.25M CH3NH2 (pka 10.6)

CH₃NH₂ + HCl => CH₃NH₃Cl

Do stoichiometry of reaction, then calculate concentration of salt (and eventually an excess of one of reagents).
Finally decide which problem you should calculate, namely:
1. buffer solution
2. an excess of strong acid
3. Hydrolysis of salt

This leads you to the concentration of H₃O⁺ (H⁺) ions and pH of solution