year 13 alevel chemistry

Hi if someone could help I would be very very thankful
at the moment in chemistry, i'm doing acids and bases and I do find it quite good, but I am trying to do homework right now and for some reason it just isn't making sense.

i need to find the concentration of NaOH using the pH which is 11
if someone could give me the steps on how to do it, I would be so happy. I don't want the answer I want to figure it out on my own!! thanks
Original post by _unknown_123
Hi if someone could help I would be very very thankful
at the moment in chemistry, i'm doing acids and bases and I do find it quite good, but I am trying to do homework right now and for some reason it just isn't making sense.

i need to find the concentration of NaOH using the pH which is 11
if someone could give me the steps on how to do it, I would be so happy. I don't want the answer I want to figure it out on my own!! thanks

What have you tried so far?
Original post by TypicalNerd
What have you tried so far?

well I know that [H+] = 10^-11 which is 1x10^-11
then i knew kw=[H+]^2 so I did that as well and got 1x10^-22 and that is all i've managed

no clue if this is right by the way just tried it out using classwork LOL
Original post by _unknown_123
well I know that [H+] = 10^-11 which is 1x10^-11
then i knew kw=[H+]^2 so I did that as well and got 1x10^-22 and that is all i've managed

no clue if this is right by the way just tried it out using classwork LOL

That isn’t quite right.

Because it’s not pure water, you can’t get away with using Kw = [H^+]^2.

Can you think of another expression for Kw and do you know the value of Kw (at 25°C)?
Original post by TypicalNerd
That isn’t quite right.

Because it’s not pure water, you can’t get away with using Kw = [H^+]^2.

Can you think of another expression for Kw and do you know the value of Kw (at 25°C)?

LMAO i thought it wasn't right, I am not good with guessing
would I use 1x10^-14 for kw, I know you use that when not given it
kw=[H+][OH-]?
Original post by _unknown_123
LMAO i thought it wasn't right, I am not good with guessing
would I use 1x10^-14 for kw, I know you use that when not given it
kw=[H+][OH-]?

Both of those are correct.

You were also correct when you deduced [H^+] = 10^-11 mol dm^-3

Now how might you proceed?
Original post by _unknown_123
LMAO i thought it wasn't right, I am not good with guessing
would I use 1x10^-14 for kw, I know you use that when not given it
kw=[H+][OH-]?

would I find [H+] then use 1x10^-14 for kw, and rearrange the equation to find [OH-]??
Original post by _unknown_123
would I find [H+] then use 1x10^-14 for kw, and rearrange the equation to find [OH-]??

That’s exactly it. Though you have already correctly found [H^+] = 10^-11 mol dm^-3

Because sodium hydroxide is a strong base, it dissociates fully in water to form one OH^- ion per NaOH dissolved, so incidentally, what does that make [OH^-] also equal to.
(edited 10 months ago)
Original post by TypicalNerd
That’s exactly it. Though you have already correctly found [H^+] = 10^-11 mol dm^-3

Because sodium hydroxide is a strong base, it dissociates fully in water to form one OH^- ion per NaOH dissolved, so incidentally, what does that make [OH^-] also equal to.

thank you so much, wow that was simple I really have a habit of not thinking and get worried when I don't understand it LOL