When rinsing your pipette to clean it, should you do your final rinse using wate

Question

When rinsing your pipette to clean it, should you do your final rinse using water? If not, what should you The volume of which physical state solid, liquid or gas is most affected by a change in temperature? If a 0.050-L sample weighs 59.6 g, what is the sample density to the correct number of significant figures? The density of a sample usually ___ (increases, decreases) as its temperature is raised. Indicate the correct reading (at the position of the arrow) on the Vernier scale below. A student adds 10.00 mL of an unknown sample to a 25,0000 g flask three times to get masses of 36, 0100 g, 47, 0211 g, and 58, 0305 g. Calculate the density of this sample.

Explanation / Answer

Ans. 1. No. The pipette shall finally be rinsed with the solution that is desired to be pipetted (immediately after cleaning).

#2. Gas.

The molecules of a gas have almost zero intermolecular attraction (when compared to those of solid and liquid). Supply of temperature increases the kinetic energy of gas molecules, all of which are free to randomly move through the provided space. So, maximum volume change upon heat transfer is observed in the gaseous state.

In solid (no freedom of movement in molecules) and liquid (limited ability to move), the molecules are held together with intermolecular (or interatomic) forces of attraction. It further hinders their ability to change volume to a considerable extent upon heat transfer- when compared to the amount of heat transfer and volume change in gases.     

#3. Density = Mass/ Volume

                        = 59.6 g/ 0.050 L

                        = 59.6 g / 50.000 mL                                               ; [1 L = 1000 mL]

                        = 1.192 g/ mL

                        = 1.2 g/ mL

Note: The number of digits after decimal (and, in turn significant figures) in the final answer must be equal to (but shall NOT exceed) the least number of digits after decimal in any of the value included for calculation.   

#4. The density of a sample usually decrease as its temperature is increased.

Increase in temperature increases the kinetic energy of molecules, so the molecules move further apart from each other. Therefore, the volume of the sample increases while mass of the sample remains constant.

Now,

            Density = mass/ Volume     - since increase in temperature increases volume, the density of sample decreases.

#6. Mass of 10.00 mL liquid after 1st addition = 36.0100 g – 25.0000 g = 11.0100 g

Mass of 10.00 mL liquid after 2nd addition = 47.0211 g – 36.0100 g = 11.0111 g

Mass of 10.00 mL liquid after 3rd addition = 58.0305 g - 47.0211 g = 11.0094 g

Average mass of 10.00 mL liquid = (11.0100 g + 11.0111 g + 11.0094 g) / 3

                                                            = 33.0305 g / 3

                                                            = 11.0102 g

Now,

Density = Mass/ Volume

                        = 11.0102 g/ 10.00 mL

                        = 1.1010 g/ mL

                        = 1.10 g/ mL

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