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Question

If you had been given a 9.1 mg sample of ibrutinib in solid form, what volume of solvent would you dissolve it in to give a final concentration of 4.7 mM? The molecular mass of ibrutinib is 440. Express your answer in number of millilitres and to two decimal places.

Answer 1

With milligrams of a substance, you are trying to find the volume needed for the concentration to equal a certain value.

You are given milligrams of ibrutinib along with the accompanying molar mass (g/mol). In order to find the number of moles present, you must divide this value by 1000. (9.1mg/1000=0.0091g ibrutinib). With the grams, you can acquire the number of moles present by dividing by the molar mass (440 g/mol). This is completed in the following equation: (0.0091g/440g/mol=0.00002068182moles ibrutinib). With moles, you can find concentration in M (molarity, or moles/L) but you are asked to acquire a concentration in mM (millimolar, or millimoles/L). In order to solve for this value, you must obtain the millimoles of substance: (0.00002068182*1000=0.02068182 millimoles ibrutinib.) Then, you can see that you want a concentration of 4.7mM (4.7 millimoles/L); to solve for the volume needed to acquire this value, simply divide the millimoles of ibrutinib by the concentration needed: (0.02068182millimoles/4.7millimoles/L=0.00440L). This is because the units cancel; when a fraction is in the denominator of another fraction, the denominator actually goes to the top (example: millimoles/L in the denominator, the L is actually going to move to the top, and the resulting unit will be L, not 1/L). So now you have the answer in L, but the question requires an answer in mL. This can be done by multiplying L by 1000: (0.00440Lx1000=4.40mL).

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