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Question
If the density of methanol is 0.793 kg L–1, what is its volume needed for making 2.5 L of its 0.25 M solution?
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Solution
Molar mass of methanol (CH3OH) = (1 × 12) + (4 × 1) + (1 × 16)
= 32 g mol–1
= 0.032 kg mol–1
Molarity of methanol solution `=(0.793" kg L"^-1)/(0.032" kg mol"^-1)`
= 24.78 mol L–1
(Since density is mass per unit volume)
Applying,
M1V1 = M2V2
(Given solution) (Solution to be prepared)
(24.78 mol L–1) V1 = (2.5 L) (0.25 mol L–1)
V1 = 0.0252 L
V1 = 25.22 mL
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