Question

Concentrated hydrochloric acid contains 37% HCl (by mass). The density of this solution is 1.18 gm/ml. The molarity of the solution is :
(a) 10 M
(b) 12 M
(c) 13 M
(d) 14 M

Answer 1

Hi Dude

Use the formula

$\% \times 10 \times density \div molar \: mass$

Using the above formula you get

37×10×1.18/36.5= 11.96 nearly equals to 12

so correct option is b

Hope answers the question

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Answer 2

(b) The molarity of the solution is 12 M

Explanation:

Given:

• 37% HCl(by mass)
• density, d = 1.18 g/mL

To find: Molarity of the solution, M

Formula Used:

• Molarity $M = \frac{n}{V}$
• number of moles $n = \frac{mass}{molar mass}$  
• density $d = \frac{mass}{Volume}$

Solution:

• 37% HCl by mass means 370 g of HCl in 1000 g solution

So, the mass of solute, HCl = 370 g

Mass of solution = 1000 g

• It is given that Density = 1.18 g/mL

Thus, the Volume of the solution $= \frac{mass}{density} =\frac { 1000 g}{1.18 g/mL}=847.45 mL = 0.847 L$

• Now, calculating the number of moles

Mass of HCl =  370 g , molar mass of HCl =  1 + 35.5 = 36.5

$n = \frac {370}{36.5} = 10.13$

• So, molarity $M = \frac{10.13}{0.847}= 11.96 M = 12 M$

Thus, the molarity of the given HCl solution is 12 M.