10% HCl

[lizzieb]

Hi all,

When I'm making a 10% soln of HCl, do I start from CONC?

Seemed simple til I started to think about it (ah, but maybe I think too much!)

Hope you're having a great Friday,

[J]

Hi Liz

The conc. HCl we buy is 35%. I'm struggling a little trying to explain the maths, but I think that 28.6ml of this solution to 71.4ml of distilled water will make a 10% solution.

Someone please correct me if I'm wrong, and explain the maths.


Julie

[Jazz]

hi,
you do start from conc if you want to make 10%. depends what is molarity you have (con usualy is 12M or 42%)
I cheat all the time by using concentration calculator. just make sure that you chose your chemical first
http://www.trimen.pl/witek/calculators/stezenia.html

[Ocean Breeze]

Firstly, check on your conc bottle to determine what is the current strength of your conc acid.

With H Cl, it could be 10 Molar or maybe 12 Molar

We have both.

10 Molar H Cl = 32 %

12 Molar H Cl = 36%
You can then do your dilution from the starting point of stated %age.

Then do your M1 x V1 = M2 x V2 equation, just substitute % for M

eg If you want 500 ml total of the 10% H Cl. Assume that we are using the 32 % conc stock acid.

M1 V1= M2 V2

32 % x V1 = 10% x 500 ml

V1 = (10 x 500) / 32

V1 = 5000/32

V1 = 156


Therefore, you need 156 ml of your 32% stock acid, MADE UP TO 500 Mls. This will give you your 10% H Cl

sorry shockong spelling

[Trudy]

Would have done the same as you Barbara - a very handy little formular that one. Can I just suggest Liz that you go back to who ever asked you for this and check that they don't just want a straight 10% solution ie the old 10mls in 100mls etc. only because it makes quite a difference to the conc. the students will use.
Cheers Trudy

[lizzieb]

Many thanks to you all!

Love that calculator, Jazz - put it straight onto favourites!

[J]

Me too!!
Who needs maths??

Julie

[lizzieb]

He's away, Trudy, or I would!
That's what brought me to ask all of you - 10mls of what molar HCl to start with?

Think I'll go with 10% of our CONC, currently 32%, as I'm confident it's doesn't have to be too precise - soaking pieces of string!!!!!
It's just that it brought up the question in my mind, and know I'd get an answer quickly on this wonderful site.
It's hte best resource I have!

Thanks to all,

[Trudy]

Sorry Liz, I think by your reply you took me the wrong way. If hes away its a bit hard, teachers are not always clear with their requests are they. It wastes alot of our precious time trying to track them down and we're not mind readers.
Good luck
Trudy

[Ocean Breeze]

You guys that use dilution calculators must have a lot more brain cells that I have! I dont ever use the tables or calculators, I have to do the maths. For the very reason, that if I dont use the maths, I will too soon forget the process of doing it manually. Then I am really stuck when I need to perform on the spot. Anyone else have that trouble?

[Trudy]

lol , know what you mean. I do it manually as well, I'm sure you can hear the cogs ginding as I try to figure out the answer some times. The calculator site does look good though

[lizzieb]

No offence taken, Trudy - I knew what you meant.
I can spend more time trying to get an answer here than it takes to get a reply from someone hundreds or thousands of kilometres away. Much more time effective to keep working and check here for replies regularly than to find someone to ask, who won't debate the answer!

I'm sure you know what I mean.

Enjoy the weekend, counting down now.....