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(i) A cake recipe uses 75 g sugar, 420 g flour and 5 g sodium hydrogencarbonate. Express the concentration of each component. (ii) A brass alloy contains 70% copper by mass. Calculate the copper and zinc in 120 g of brass.
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(i) Total mass = 75 + 420 + 5 = 500 g. Using mass by mass %:
Sugar = \( \dfrac{75}{500}\times100 = 15\% \); Flour = \( \dfrac{420}{500}\times100 = 84\% \); Sodium hydrogencarbonate = \( \dfrac{5}{500}\times100 = 1\% \).
(ii) Copper = 70% of 120 g = \( \dfrac{70}{100}\times120 = 84 \) g. Zinc = 120 − 84 = 36 g.
← Back to concept: 5.2.2 Expressing concentration