Acid-Base Equilib: Solving Homework Problem

[Veronica_Oles]

Homework Statement

To unclog a drain you add 26g of sodium hydroxide to 150mL of water. Calculate the pH and pOH for the solution you prepared. Can someone tell me if I'm doing it right.

Homework Equations

The Attempt at a Solution

n = m/M
n = 26/40
n = 0.65mol for 0.15L

Does this mean that I have to convert into mol/L?

So that would be 4.33 mol/L and this would also be my H⁺ value/ And then would I plug it into my equation

pH = -log[H⁺] and find my pH value.

Then plug my pH value into my pH + pOH = 14 equation and solve for pOH?

Is this the correct method?

 

[Borek]

So that would be 4.33 mol/L and this would also be my H+ value

No.

Trivial mistake, but you got it reversed. NaOH doesn't produce H⁺ when dissociating. Other than that, you are on the right track.

Actually the final concentration is a bit lower than 4.33 M as the volume is not 150 mL, it gets a bit higher after NaOH dissolution. But you can safely ignore it.

 

[Veronica_Oles]

No.

Trivial mistake, but you got it reversed. NaOH doesn't produce H⁺ when dissociating. Other than that, you are on the right track.

Actually the final concentration is a bit lower than 4.33 M as the volume is not 150 mL, it gets a bit higher after NaOH dissolution. But you can safely ignore it.

Sorry I meant to put OH^-

okay here's what I've gotten

NaOH = 26/40 = 0.65mol

And 0.65 mol would be my 0.65 mol/L?

 

[Veronica_Oles]

Sorry I meant to put OH^-

okay here's what I've gotten

NaOH = 26/40 = 0.65mol

And 0.65 mol would be my 0.65 mol/L?

I put that value into my pOH equation and ended up with 0.187

I then put that into the next equation
pH = 14 - pOH and got
pH = 13.81

Is this correct or way off?

 

[Borek]

NaOH = 26/40 = 0.65mol

And 0.65 mol would be my 0.65 mol/L?

No, you have to take the volume into account, Actually you did it - and correctly - in your first post.

 

[Veronica_Oles]

No, you have to take the volume into account, Actually you did it - and correctly - in your first post.

Okay so basically I'm using the formula c= n/v?

 

[Borek]

Yes, just like you did initially.