silly gen chem question

[slawson]

hey guys i've been studying for the oat with the kaplan flashcards and i feel really silly but i cant remember how to do this question..

Q: Would the pH of 1.4X10^-4 MHCL solution be greater than 4 or less than 4?

thanks

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[gochi]

hey guys i've been studying for the oat with the kaplan flashcards and i feel really silly but i cant remember how to do this question..

Q: Would the pH of 1.4X10^-4 MHCL solution be greater than 4 or less than 4?

thanks

This is how I would approach it..

HCL --> H+ + CL-
1M 1M 1M

pH=-Log[H+]= -log 1.4E-4 ~ 3.8 so less than 4.

But how the heck do you do it w/o a calc!!

 

[mwyt15]

This is how I would approach it..

HCL --> H+ + CL-
1M 1M 1M

pH=-Log[H+]= -log 1.4E-4 ~ 3.8 so less than 4.

But how the heck do you do it w/o a calc!!

Well, since 1E-4 M of HCl solution has a pH of 4...1.4E-4 M is more concentrated than 1E-4 M...and since HCl is a strong acid so we know that HCl will totally dissociate in solution and form H+ ions and Cl- ions, we know that there will be MORE H+ ions in 1.4E-4 M HCl than there are in 1E-4 M HCl. More H+ ions in solution means that the pH of the solution will be less than 4. Hope this helps.

 

[Optoroboto]

hey guys i've been studying for the oat with the kaplan flashcards and i feel really silly but i cant remember how to do this question..

Q: Would the pH of 1.4X10^-4 MHCL solution be greater than 4 or less than 4?

thanks

1.4 X 10^-4=> (algorithms)=> -4 + log 1.4 or 4 - log1.4= LESS THAN 4.

I think this is right. hope this helps