Question

Part A
[H3O+] = 2.1×10−4 M
Express your answer using two significant figures.

[OH−] = M
  

Part B

A.)	This solution is acidic.
B.)	This solution is basic.
C.)	This solution is neutral.

Answer 1

Answer – Part A) We are given, [H₃O⁺] = 2.1*10^-4 M

We are asking for the [OH^-] = ? M

We know the ionic product

Kw = [H₃O⁺][OH^-]

1.0*10^-14 = 2.1*10^-4 M *[OH^-]

[OH^-] = 1.0*10^-14 / 2.1*10^-4 M

          = 4.8*10^-11 M

Part B) We know when [H₃O⁺] = [OH^-] then there is neutral solution and when [H₃O⁺] < [OH^-] then there is basic solution, since the hydroxide ion is greater than protons and gives the pH more than 7.

When [H₃O⁺] > [OH^-] then there is acidic solution, since the proton ion is greater than hydroxide and gives the pH less than 7.

So in this one there is given, [H₃O⁺] = 2.1*10^-4 M and we calculated

[OH^-] = 4.8*10^-11 M

[H₃O⁺] > [OH^-], so A) This solution is acidic