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WAEC Physics 2014 Paper

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Question : 12

Total: 48

Alcohol of mass 21g and density 0.7g cm^-3 is mixed with 10g of water. Determine the density of the mixture [density of water = 1.0gcm^-3]

0.775gcm^-3
0.875gcm^-3
0.780gcm^-3
0.880gcm^-3

Solution:

Concept:

The density of a mixture is found using the total mass of the mixture divided by its total volume.

Explanation:

Volume of alcohol:

V_A = \frac{21\text{ g}}{0.7\text{ g cm}^{-3}} = 30\text{ cm}^3

Volume of water:

V_w = \frac{10\text{ g}}{1.0\text{ g cm}^{-3}} = 10\text{ cm}^3

Total volume of mixture:

V = 30 + 10 = 40\text{ cm}^3

Total mass of mixture:

M = 21 + 10 = 31\text{ g}

Density of mixture:

D = \frac{M}{V} = \frac{31}{40} = 0.775\text{ g cm}^{-3}

Answer:

A.

0.775\text{ g cm}^{-3}

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