Design:
Research Question: How does the density of a liquid affect the volume of a drop?
Hypothesis: If density is inversely proportional to volume (mass/volume=density), then as the density of the liquid increases, the volume decreases. Similarly, as the density decreases, the volume will increase.
Variables:
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Independent: Mass (amount of liquid), Density
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Dependent: Volume
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Controls: Temperature (of room and liquid), Pressure (of room and liquid), pressure applied to pipet, type of pipet, Equipment used
Materials:
-Disposable Pipet
-2 Empty Containers
-100 g liquid sample
-Thermometer (-10°C to 110°C 0.2°C)
-Balance (to 0.001 ± 0.0001 g)
-Barometer (0-30 atm)
-Ringstand
-Clump
-Calculator
-100 mL graduated Cylinder
Procedure:
- Obtain the temperature of the room and liquid using a thermometer and the pressure of the room and liquid using a barometer. Record your findings.
FOR COLUMN A:
- Weigh the mass of the empty container on the balance. Record its mass (to .001 g)
- Pour about 2/3 of the 100 g liquid sample into the container. Record the combined mass of the liquid and container. Then get mass by difference to figure out the mass of the liquid sample.
- Find the moles of liquid using molar mass
- Transfer the sample into the disposable pipet and let it drop into a 100mL graduated cylinder
- Using the Ideal Gas Law (PV=nRT), find the volume of this sample of liquid. P would be the pressure of the liquid, n would be the moles, R would be the constant of 0.0821mol(K)/L(atm), and T would be the temperature.
FOR COLUMN B:
- Record the temperature and pressure again to make sure these numbers are relatively the same as it was in the first set of procedures.
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Repeat the same procedures as the first set, except this time changing your data according to the new set of mass you obtain from the leftover liquid in the 2nd container.
- Rinse out the pipet and make sure it is dry before transferring the liquid.
- Make sure to apply relatively the same amount of pressure when squeezing the bulb of the pipet to release the drops.
- Record this set of data in order to calculate the volume
- Compare the two volumes that were obtained in both these sets of procedures with the density using D=M/V – where D stands for density, M for mass, and V for volume.
Errors that may occur:
Human error: We might have observed it incorrectly or misinterpreted a step.
Instrumental limitations: A digital balance showing three decimal places can only weigh to within 0.0005 g by its very nature and even then only if it rounds the figures to those three places.
Also, analogue devices such as thermometers or pipets and graduated cylinders often require the observer to interpolate between graduations on the scale. Some people will be better at this than others.
Observing: For example, to measure the temperature of the liquid sample, you will dip a thermometer into it. This will inevitably cool the liquid slightly. The amount of cooling is unlikely to be a source of major error, but it is there nevertheless
External Influences: The balance or other equipment may not be accurate and we also have to take in consider the impurity of the liquid sample.
Sampling: Just these two sets of experimental procedures may not be enough to completely determine accurately the intended purpose for this experiment. Therefore, there may not be enough evidence to support the hypothesis.