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Solve the following problems:
(i) A cake recipe uses dry ingredients, namely 75 g of sugar for 420 g of all-purpose flour and 5 g of sodium hydrogencarbonate. Express the concentration of each component in the mixture using an appropriate method.
(ii) A brass alloy contains 70% copper by mass. Calculate the quantities of copper and zinc present in 120 g of brass.
(i) A cake recipe uses dry ingredients, namely 75 g of sugar for 420 g of all-purpose flour and 5 g of sodium hydrogencarbonate. Express the concentration of each component in the mixture using an appropriate method.
(ii) A brass alloy contains 70% copper by mass. Calculate the quantities of copper and zinc present in 120 g of brass.
View Answer
(i) Total mass = 75 + 420 + 5 = 500 g. Using mass by mass %:
Sugar = 75 500 ×100 = 15% ; Flour = 420 500 ×100 = 84% ; Sodium hydrogencarbonate = 5 500 ×100 = 1% .
(ii) Copper = 70% of 120 g = 70 100 ×120 = 84 g. Zinc = 120 − 84 = 36 g.
Working Out the Concentrations
Total mass of the cake mixture
75 + 420 + 5 =
500 g
↓
%
m/m
of each
sugar
15 %
· flour
84 %
· sodium hydrogencarbonate
1 %
↓
Brass: 70 % copper of 120 g
copper =
84 g
↓
Zinc = 120 − 84 =
36 g
