There are two samples of HCl having concentrations of 1 M and 0.25 M. Find amongst the given options, the combination of these samples needed to prepare a 0.75 M HCl solution assuming no extra water is used.
A
20 mL, 10 mL
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B
100 mL, 60 mL
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C
50 mL, 20 mL
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D
50 mL, 35 mL
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Solution
The correct option is A 20 mL, 10 mL Let the volume of 1 M solution be V1 and volume of 0.25 M solution be V2. Conserving moles before and after dilution: M1V1+M2V2=MV where M and V are the final molarity and volume. 0.75×(V1+V2)=(1×V1)+(0.25×V2) On solving, V1V2=21 From the options, option (a) will match the ratio of volumes. Therefore, 20 mL of 1 M solution and 10 mL of 0.25 M solution should be mixed.