Question

Suppose you wanted to produce an aqueous solution of pH = 8.75 by dissolving one of the following salts in water: NH4Cl, KHSO4, KNO2, NaNO3
Which salt would you use and what would its molarity need to be?

Answer 1

@Cuanchi

Answer 2

I chose KNO2 and figured out the molarity like this:

Answer 3

And rounded to 1.6 M to two sig figs.

Answer 4

But apparently, that is wrong.

Answer 5

what are the other answers?

Answer 6

It is fill in the blank. The choice of KNO2 was correct, by the way.

Answer 7

ok cool

Answer 8

@Michele_Laino

Answer 9

@aaronq @chmvijay @JFraser @jim_thompson5910

Answer 10

Oh, would it have to do with that K+ would make KOH?

Answer 11

Nevermind, I don't think that's it.

Answer 12

@Michele_Laino Any thoughts?

Answer 13

@abb0t

Answer 14

I'm thinking...

Answer 15

Sure :-) Thanks so much!

Answer 16

I'm sorry I don't know this answer

Answer 17

Ok. Thanks for looking.

Answer 18

Do you know anyone who might be able to help? @Michele_Laino

Answer 19

@rvc

Answer 20

you'd want to use a weak acid whose pKa is closest to the pH you want to obtain. Use an ICE table approach to find the molarity of the solution

knowing the pH lets you find the [H+] needed, and the [OH-] needed, so the ICE table approach is the most straightforward, I think

Answer 21

Thanks, @JFraser! But that's what I did, right?

Answer 22

@IrishBoy123

Answer 23

@JFraser Do get a different solution than what I have posted?

Answer 24

Are you sure the Ka you used for HNO3 was correct?

this table http://depts.washington.edu/eooptic/links/acidstrength.html
lists it at 24

Answer 25

I am using the Ka for HNO2 @aaronq

Answer 26

oh sorry. Hm it should be right then, do you think they're very picky about carrying through with sig figs?

Answer 27

I don't think so.

Answer 28

:/

Answer 29

Hm, I'm glad it's not just me, but... *sigh

Answer 30

i haven't done out the calculations, so it'll take time to check

Answer 31

looks pretty fine the logic. This calculation is very sensitive to the value of pKa that you use. Depend of the source of that information some tables gives values of pKa of 3.25 (CRC catalog) 3.29 (your data), 3.34 (Tro 2nd Ed.) and other 3.39 (Zumdahl 6th Ed.).

That can give you a result between 1.8 - 1.3 M.

http://www.hbcpnetbase.com/tables/loadtable.asp?id=05_24_92&page=&rows=41&orderFieldName=&orderFieldFormatter=&orderFieldDirection=&tableFilter=&tableFilterData=&deliveryTarget=

http://clas.sa.ucsb.edu/staff/Resource%20folder/Chem109ABC/Acid,%20Base%20Strength/Table%20of%20Acids%20w%20Kas%20and%20pKas.pdf

https://en.wikipedia.org/wiki/Nitrous_acid

pKa Cs
3.24 1.82
3.25 1.78
3.26 1.74
3.27 1.70
3.28 1.66
3.29 1.62
3.3 1.58
3.31 1.55
3.32 1.51
3.33 1.48
3.34 1.45
3.35 1.41
3.36 1.38
3.37 1.35
3.38 1.32
3.39 1.29
3.4 1.26
3.41 1.23

Answer 32

Wow, that makes sense. Thanks, @Cuanchi !

Answer 33

KOH is a strong base. I doubt that you would of used that to begin with.

Answer 34

Yeah, I didn't. Just trying to figure out why I'm getting it wrong according to the computer.