It is often necessary to prepare a dilute solution from a more concentrated solu

Question

It is often necessary to prepare a dilute solution from a more concentrated solution rather than starting from a solid and just dissolving it then adding water. This technique is called serial dilution. Give all the steps necessary to obtain 100 mL of a 1.7 X 10-5 M solution using serial dilution. (Hint: One must start with a concentrated solution). The required laboratory equipment and compound information are given: 0.3 grams of a compound with a molar mass of 869 g/mol, deionized water, 1.0 mL pipette, 5.0 mL pipette, 10.0 mL pipette and two - 100.0 mL volumetric flasks.

Explanation / Answer

100 ml of 1.7*10-5 M solution contains 1.7*10-6 moles of the compound

Now, moles of the compound in 0.3 g of it = mass/molar mass = 0.3/869 = 3.45*10-4

Now, Molarity = moles of solute/volume of solution in litre

or, volume of solution in litres = moles of solute/molarity = (3.45*10-4)/(1.7*10-5) = 20.31 litres

Now, mass of compound containing 1.7*10-6 moles = 1.7*10-6*869 = 0.0015

Thus, weigh out 0.0015 g of the compound and dilute it to 100 ml in a 100.0 mL volumetric flask

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