Question

How many grams of potassium chloride (KCl) must be added to make 500 ml of M KCl solution?
A. 1.00g
B. 18.6g
C. 37.3g
D. 74.5g
E. 149g

Answer 1

Hint In order to solve this question, one must have the knowledge of molarity. As we know that molarity is the ratio of number of moles of solute in volume of solution. Molarity is denoted by M.

Complete Step by step solution:
- As we have to find the grams of potassium chloride (KCl) that must be added to make 500 ml of M KCl solution. So, we can calculate it as:
- As we know that 1000 ml of 1 M KCl contains about 74.5 g of KCl.
- So, 1 ml of 1 M KCl contains about 74.5 / 1000 grams of KCl.
- Now, 500 ml of 1 M KCl contains about (74.5 / 1000) X 500 gm of KCl.
- By solving, we get the value as:
0.0745 X 500
=37.3 g

- Hence, we can conclude that the correct answer is option (c), that is 37.3 g grams of potassium chloride (KCl) must be added to make 500 ml of M KCl solution.

Note:
- We should not get confused in the terms molality and molarity. As, molality is the ratio of the number of moles of solute in kg of solvent. Molality is denoted by m.
- Whereas molarity is the ratio of number of moles of solute in volume of solution. Molarity is denoted by M.
- One should not forget to write the unit in the solution.