Relationship between Ph and mass?

[Aletheia]

---

Members don't see this ad.

What do I need to know (formula etc) to solve a question like this. Thanks.

What mass of HCl is present in 0.250 L of a solution with a pH of 2.85?

 

[RogueUnicorn]

think about it. what does the pH tell you about HCl. can you use it to calculate some value directly related to HCl?

 

[wanderer]

Dimensional analysis. (X/Y) * (A/B) * (Y/A) .......
A lot of chemistry questions involving stuff like mass comes down to this. Make sure you can do it with celerity.

 

[ezsanche]

How many moles of HCL are in the solution? (hint the number of H+ = the number of HCL)

 

[SolidWater]

-

 

[SolidWater]

-

 

[RogueUnicorn]

ph=-log[H+]

What mass of HCl is present in 0.250 L of a solution with a pH of 2.85?

2.85 = -log[H+]

Log is base 10, so you can see that the concentration of hydronium ions, as the above mentioned is the same as the liters of HCL, since HCL is a strong acid and will completely dissociate into CL- and H+...

Therefore,

[H+] = 10^(-2.85) ; this is the number of moles in one liter and you are given only 1/4 of a liter (0.250 L).

So, using D.A.: (10^(-2.85))*(.25) = 3.5x10^-4 moles of HCL * Molecular Weight of HCL = Answer.

Hope that's what you were looking for! If it's not clear let me know and I'll explain. 😉

catch a hungry man a fish.... or teach him how...

 

[SolidWater]

=

 

[Aletheia]

I completely forgot my log rules, but now that I've brushed up on them and on my acids and bases, I think I've got it. Thanks all!

For anyone that wants to know:

2.85=-log (H+)
=1.41x10^-3 ions in moles H/Liter of solution *.250 L *HCL/H*gHCL/moles HCL = .012

Edit: And in the time it took me to type that, SolidWater posted the same response, in case you're wondering why there's double. Thanks!

 

[ezsanche]

Hmmm.

How about this question: pH literally means "log of H" right? so when you see pKa, etc, it's log of Ka...why then is it negative not positive log of the number? I mean I understand why...otherwise you'd have a HUGE amount of hcl/whatever per liter... is that not possible?

Actually p means NEGATIVE LOG OF...

 

[boaz]

Dimensional analysis. (X/Y) * (A/B) * (Y/A) .......
A lot of chemistry questions involving stuff like mass comes down to this. Make sure you can do it with celerity.

Wow, you are cool 😎


😛

catch a hungry man a fish.... or teach him how...

👍