Page 13 - 11-chem-9

9.SOLUTIONS eLearn.Punjab

Example (7):

Hydrochloric acid available in the laboratory is 36% (w/w). The density of HCl solution is 1.19
g cm-3. Determine the molarity of HCl solution.

Solution:

36% (w/w) HCl solution means that 36g of HCI dissolved in 100g of solution.

Mass of HCl =36g

Mass of solution =100g

In case of molarity, the final volume of solution is 1000 cm3. Convert this volume into mass,
by using density of 1.19 gcm-3.

Mass of 1000cm3 of HCl solution =1000x1.19 =1190g

Since, (Mass=volume x density)

100g of solution has HCl =36g

so, mass of HCl in 1190g of solution = 1190x36 =428.4g
100g

Molar mass of HCl =36.5g mol-1

Number of moles of HCl, in 428.4g of HCl = 428.4g =11.73
36.5gmol-1

So, 1000 cm3 solution of HCl has 11.73 moles of HCl

Hence, molarity of HCl =11.73mol dm-3 Answer

Example (8):

9.2 molar HClO4 is available in the market. The density of this solution is 1.54gcm3. What is the
percentage by weight of HClO4.

13