HCI is a liquid with molecular weight of 36.5 g/mol. Usually Hcl is sold as a so
ID: 475693 • Letter: H
Question
HCI is a liquid with molecular weight of 36.5 g/mol. Usually Hcl is sold as a solution, and figuring out how to prepare necessary dilutions could be tricky. We will try to do it step by step Calculate the theoretical dry mass in g of HCI to make 100 ml of 10 mM solution of HCI. Since HCI is not a solid, but rather a liquid, we need to measure the amount of stock HCI in ml, not in grams. If the density of HCI solution is 1.27 g/ml, how many ml of liquid 100% HCI (instead of grams you easily calculated in the previous step) do you need to take to prepare 100 ml of 10 mM solution of HCl? You have 37% HCI solution (density is always 1.27 g/ml). Calculate the amount of this solution you need to take to prepare 100 ml of 10 mM of HCl calculate the theoretical pH of this solution (HCI is a strong acid and dissociates completely).Explanation / Answer
Molecular weight of HCl = 36.5 g/mol
a)
Volume = 100 mL = 0.1 L
Molarity = 10 mM
Moles of HCl required = Volume * Molarity
= 0.1 * 10 mmoles = 1 mmoles = 10-3 moles
Dry mass of HCl required = Moles * Mw
= 10-3 * 36.5 = 0.0365 g
b)
Density of stock 100% HCl = 1.27 g/mL
Volume of 100 % HCl required = Dry mass of HCl / Density
= 0.0365 / 1.27 = 0.02874 mL
c)
Density of 37 % HCl = 1.27 g/mL
Mass of HCl present in 1 mL = 1.27 * 37 / 100 = 0.47 g / mL
Volume of HCL required = Dry mass / Mass of HCl present in 1 mL
= 0.0365 / 0.47 = 0.078 mL
d)
Molarity of HCl = 10 mM = 10-2 M
[H+] = 10-2 M (Given complete dissociation)
pH = - log ([H+]) = - log ( 10-2)
pH = 2
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