You wish to prepare 50.00 mL of 0.0450 M NH 3 from concentrated ammonia (15.28 M

Question

You wish to prepare 50.00 mL of 0.0450 M NH3 from concentrated ammonia (15.28 M) by serial dilution using a 50 mL volumetric flasks, a 2.00 mL volumetric pipet, and a 10.00 mL graduated pipet.

For the first dilution in the series, 2 mL of concentrated ammonia is added to a 50.00 volumetric flask and then filled to the line. The solution is mixed thoroughly, poured into a beaker, and then used to make the second solution in the series. What volume of the first solution should be used to make the second solution, 50.00 mL of 0.0450 M NH3 solution, using the glassware provided?

Explanation / Answer

For the first dilution : -

According to law of dilution   MV = M'V'

Where M = Molarity of concentrated solution = 15.28 M

V = Volume of the stock = 2 mL

M' = Molarity of dilute solution = ?

V' = Volume of the dilute solution = 50 mL

Plug the values we get   , M' = MV /V'

                                              = (15.28 x 2 ) / 50

                                              = 0.6112 M

For the second dilution : -

According to law of dilution   M'V' = M''V''

Where M' = Molarity of first diluted solution = 0.6112 M

V' = Volume of the first diluted solution taken = ?

M'' = Molarity of dilute solution = 0.0450 M

V'' = Volume of the dilute solution = 50.00 mL

Plug the values we get   , V' = M"V" / M'

                                              = (0.0450 x 50 ) / 0.6112

                                              = 3.68 mL

Therefore the volume of first diluted solution taken is 3.68 mL

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