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Liquid A has a density of 1.42 g/cm³

7 cm³ of liquid A is mixed with 125 cm of liquid B to make liquid C.
Liquid C has a density of 1.05 g/cm³.
Find the density of liquid B.
Give your answer correct to 2 decimal places.​

1 Answer

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Explanation:

if I understand correctly, then we are mixing 7 cm³ of liquid A with 125 cm³ of liquid B to a liquid C.

A has a density of 1.42 g/cm³.

B has a density of x g/cm³.

the resulting C has a density of 1.05 g/cm³.

the first thing we see is the quantity of C :

C = A + B = 7 + 125 = 132 cm³

what "comes in" must also "come out" again.

there is no mentioning of a chemical reaction, that might cause a change of volume or mass of the mixture.

so, the whole is exactly the sum of its ingredients.

now about mass and density :

as also the mass (g) of the resulting C must be the same as the sum of the masses of A and B, we multiply the density by the quantity of every liquid to get the mass (g). and that is how we get then the missing density of B :

7×1.42 + 125x = 1.05×(7+125)

9.94 + 125x = 1.05×132 = 138.6

125x = 128.66

x = 1.02928 ≈ 1.03 g/cm³

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