Agata Łuszczyńska 29.09.2007
II LO im. Stefana Batorego

Investigate the volume of a drop

Design		DCP		CE
1 asp		1 asp		1 asp
2 asp		2 asp		2 asp
3 asp		3 asp		3 asp
sum		sum		sum

The volume of a drop can differ much from each other. Changing the pressure, temperature, the diameter of the pipette can greatly influence the volume. However for different needs the volume of a single drop was standardized to a volume from ¹/₂₀ to ¹/₁₀ ml.

For my investigation I tried to determine if the density of a solution can influence the volume of such drop.

Apparatus:

• An electronic scale ± 0.1 g

• A pipette

• Beakers

Reagents:

• Water

• Ethanol

• Sodium chloride

Variables:
Dependent: Concentration of a compound dissolve in water	Independent: Volume of a drop	Controlled: Temperature of the air Temperature of the reagents Pressure Diameter of the pipette

Procedure:

Firstly I will measure the weight of an empty beaker with an electronic scale. Then I will instill 50 drops of water with the pipette into the beaker and weight it. The weight of the liquid can be achieved by subtracting the weight of an empty beaker from the weight of a full beaker Then using a formula for the density I will calculate the volume of fifty drops a solution and divide it by fifty achieving the volume of a single drop. I will follow the same steps with the ethanol and the sodium chloride (20%). All of it I will repeat three times to assure myself with the results. The best way to collect the data will be a table

	Weight of an empty beaker [±0.1g]	Weight of a full beaker [±0.1g]	Mass of liquid [±0.2g]
Probe 1
Probe 2
Probe 3

Data collection and processing:

Raw data:

Water

	Weight of an empty beaker [±0.1g]	Weight of a full beaker [±0.1g]	Mass of liquid [±0.2g]
Probe 1	51.3	54.9	3.6
Probe 2	51.3	55.1	3.8
Probe 3	51.4	55.0	3.6

Ethanol

	Weight of an empty beaker [±0.1g]	Weight of a full beaker [±0.1g]	Mass of liquid [±0.2g]
Probe 1	51.2	52.4	1.2
Probe 2	51.2	52.6	1.4
Probe 3	51.4	52.7	1.3

Sodium chloride 20%

	Weight of an empty beaker [±0.1g]	Weight of a full beaker [±0.1g]	Mass of liquid [±0.2g]
Probe 1	51.5	55.7	4.2
Probe 2	51.4	55.4	4
Probe 3	51.4	55.5	4.1

Processing raw data:

d_water = 1 g/cm³

d_ethanol = 0.79 g/cm³

d_{NaCl 20%} = 1.25 g/cm³

I will use the following equation:

d = m/V

where: d - density m - mass V - volume

so: V = m/d

Then the volume of the liquids is:

Water:

	Volume of the liquid [±0.2ml]	Volume of one drop [±0.004ml]
Probe 1	3.6	0.072
Probe 2	3.8	0.076
Probe 3	3.6	0.072
Average volume		0.073

Ethanol:

	Volume of the liquid [±0.2ml]	Volume of one drop [±0.004ml]
Probe 1	1.51	0.030
Probe 2	1.77	0.035
Probe 3	1.65	0.033
Average volume		0.033

Sodium Chloride 20%

	Volume of the liquid [±0.2ml]	Volume of one drop [±0.004ml]
Probe 1	3.36	0.067
Probe 2	3.20	0.064
Probe 3	3.28	0.066
Average volume		0.066

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