If you are working from the label data you always use the lower end of the range. If the concentration is important to your work then you run an assay on the HCl to obtain the true concentration.

Use the equation in the USP!

The molar concentration of 36% HCl is reported to be 11.65 M and the density is reported to be 1.18 g/cm3.

I get that result based on the following calculation, assuming that the % is a (w/w)%.

(36 g HCl/100 g solution) x (1190 g solution/L) x (mol/36.46 g) = 11.65 M

For calculating use formula:

number of moles = weight (given on bottle) / molecular weight (HCl)

therefore, take average (36.5+38/2=37.3) i.e. 37.3 g in 100 ml (37.3%)

=373 g in 1000 ml

(molarity is number of moles in 1000 ml of solution)

Molarity = 373/ 36.5g x specific gravity (HCl)

=10.21 x specific gravity (1.19)

=12.15 M

Thus the concentration of the HCl (inside the bottle) is 12.15 M.

Later, by N1V1=N2V2 you can calculate the volume of concentrated HCl needed

e.g. if you want to make 5 ml of 1M of HCl,

then 12.15M x X (X is unknown) = 1M x 5

Therefore X= 5/12.15

=0.41 ml

Hence take 0.41 ml of of concentrated HCl and make final volume to 5 ml with DDW.

Hi,

You may calculate the concentrate of hydrochloric acid 36.5% and 38%, respectively. And the exact concentrate of hydrochloric acid is between the two calculation results.

Chen Jingwen thank you so much

Mark Krause thank you so much

Adam B Shapiro Bruce Neagle Bhairavi Vajaria thank you so much

https://www.sigmaaldrich.com/catalog/product/sigma/h1758?lang=en®ion=US

In the scheme of things who cares? If you need the exact value either buy a standard or titrate the HCl using standardized materials. This is a reagent that has a concentration somewhere in that range. There are tables giving you the rough molarity of the reagent acid and caustics and amounts necessary to build a 1M solution of each.

Bruce Neagle could you possibly help me use the USP equation to calculate % HCl? I am struggling with the N for the titrant... it's 1.001N Sodium Hydroxide, but the formula requires units of mEq/mL, would it also be 1.001?!

Your last question is yes. Assuming ALL the molecules of NaOH dissociate into Na+ and OH- ions (a good assumption for a strong acid or base) then 1 M (mole/liter) = 1 N (normal/liter) solution. Similarly a 1.001 N Sodium Hydroxide solution is 1 Normal or 1 Equivalent per L. Since, there 1000 milliequivalents in 1 Equivalent, a 1 N solution can also be called 1 meq/mL.