Everything Science Grade 10

19.3 CHAPTER 19. QUANTITATIVE ASPECTS OF CHEMICAL CHANGE

Example 13: Concentration Calculations 2

QUESTION

You have a 1 dm^3 container in which to prepare a solution of potassium per-

manganate (KMnO 4 ). What mass of KMnO 4 is needed to make a solution with a

concentration of 0 , 2 mol·dm−^3?

SOLUTION

Step 1:Calculate the number of moles

C=Vn therefore:

n=C×V= 0, 2 mol·dm−^3 × 1 dm−^3 = 0, 2 mol

Step 2:Find the mass

m=n×M= 0, 2 mol× 158 g·mol−^1 = 31, 6 g

The mass of KMnO 4 that is needed is 31 , 6 g.

Example 14: Concentration Calculations 3

QUESTION

How much sodium chloride (in g) will one need to prepare 500 cm^3 of solution

with a concentration of 0 , 01 mol·dm−^3?

SOLUTION

Step 1:Convert the given volume to the correct units

V= 500cm^31 dm

3

1000 cm^3 = 0,^5 dm

3

Step 2:Find the number of moles

352 Chemistry: Chemical change