May 31, 2023, 05:08:48 AM
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### Topic: Pharmacopeia dilution help  (Read 705 times)

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#### PeterS

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##### Pharmacopeia dilution help
« on: April 02, 2023, 07:24:16 AM »
Problem:
Hydrochloric acid R1. 1043501. Contains 250 g/L of HCl. Dilute 70 g of hydrochloric acid R to 100 mL with water R.

How many ml of the concentrated HCl R (D = 1,19 g/mL; Ar= 36,45 g/mol; w(HCl) = 37 %) do we need to prepare 500 mL of hydrochloric acid R1?
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My calculations:
70 g of HCl R in 100ml solution ->  350 g of HCl R in 500ml solution
volume = mass/density -> 350g/1,19 g/ml -> 294 ml

However the correct answer is 284ml. Can anyone point out the mistake that I've made?

#### Hunter2

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##### Re: Pharmacopeia dilution help
« Reply #1 on: April 02, 2023, 08:16:50 AM »
I got the same result. Must be a mistyping in the solution.
70 g R is equal to 58,82 ml. This i needed for 100 ml R1. For 500 ml we need 5 times means 294,11 ml

#### PeterS

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##### Re: Pharmacopeia dilution help
« Reply #2 on: April 02, 2023, 11:43:58 AM »
Found the error.

Hydrochloric acid R is defined as "35,5-37%" while the problem specifies 37%.

Hence, starting from " Contains 250 g/L of HCl" -> 125g of HCl per 500 ml.

w(100)/w(37)= 2.7 -> 125g of HCl * 2.7 = 337.8 g 37% HCl -> 284ml.