In an experiment, a student was asked to measure the densities of liquid acetone

Question

In an experiment, a student was asked to measure the densities of liquid acetone and metallic chromium. He was given a pycnometer which weighed 26.880 g empty. When filled with water and stoppered, the mass was recorded as 54.992g at 28°C. The pycnometer was cleaned and filled with acetone. The mass was 49.137 g. Again, the flask was cleaned and dried. Into it were added some chunks of chromium and the total was found to weight 78.666 g. Leaving the chromium in the pycnometer, it was then filled with acetone. The flask, metal and acetone was found to weigh 95.199 g. From this data, calculate the density of acetone and the density of chromium (show all your calculations).

Explanation / Answer

Answer

Weight of empty pycnometer = 26.880g

Weight of pycnometer and water = 54.992g at 28o C

Thus, weight of water = (54.992 - 26.880)g = 28.112g

Since, desity of water at 28o C = 0.996g / ml (experimentally known)

so, volume of water = (weight / density) = 28.112 / 0.996 = 28.225 ml

Thus volume of pycnometer will also be 28.225 ml.

Now,

Mass of pycnometer and acetone = 49.137g

Mass of acetone = (49.137 - 26.880) = 22.257 g

Volume will be equal to the volume of pycnometer = 28.225 ml

Thus, density of acetone = (mass / volume) = ( 22.257 / 28.225) g / ml

= 0.7885 g /ml

Now,

Mass of chromium and pycnometer = 78.666 g

Mass of chromium = (78.666 - 26.880) = 51.786 g

Mass of chromium, pycnometer and acetone = 95.199g

Here, mass of acetone = Mass of chromium, pycnometer and acetone - Mass of chromium and pycnometer

= 95.119 - 78.666 = 16.453g

Since, density of acetone (already calculated above) = 0.7885 g /ml

Here, Volume of acetone = (mass / density) = 16.453 / 0.7885

= 20.866 ml

Since, Out of 28.225 ml volume of pycnometer, 20.886 ml volume is occupied by acetone. Thus,remaining volume is occupied by chromium.

Now, volume of chromium = 28.225 - 20.866 = 7.358 ml

thus, density of chromium = (mass / volume) = 51.786 / 7.358 =7.038 g / ml

Thus,

Density of acetone = 0.7885 g / ml

Density of chromium = 7.038g / ml

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