Experiment 1

Basic Laboratory TechniquesParts A, D, E, and an Unknown

(work in groups of 2)

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Purpose of This Experiment

• Determining the SF and value from calibrated equipment

• Use a laboratory balance• Use a pipet• Calculating a mean and deviation from the

mean • Determine the density of two liquids (antifreeze and an unknown)

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Calibration Scales

• Know how to read the calibration marks on a piece of calibrated equipment and determine:

1. the correct number of significant figures2. the correct volume reading

Part A uses a meter stick; please do this part at home with a ruler

Part D uses a pipet and balancePart E uses a pipet and balance

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• The ± values listed in Table 1.4 on page 6 do not always match up with the equipment we have.

Meter stick: ± is 0.01cm in theory, but use the ±0.1 cm because it is more practical for human eyes

Graduated cylinder: ± depends on sizeLaboratory balance: ±0.01g or ±0.001g

(check readout)

Pipet: only one calibration line, ± depends on quality of pipet

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Reading A Calibration ScaleIn General:1. Find difference between numbered tick marks2. Use the un-numbered tick marks between the two

numbered marks to count the number of jumps from one numbered mark to the other

3. Determine what each un-numbered mark is worth4. Estimate one digit beyond the un-numbered tick marks

(this is the last significant digit for the measurement)5. Read the measurement, using the correct number of

significant figures

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Part A: The Meter Stick• Use your lab book for object to measure• Measure length and width of book using the inch

calibration side of ruler (use ¼ as the smallest division of an inch; .00, .25, .50, .75)

• Measure length and width of book using the metric side of ruler. Take all measurements in units of cm, use ± 0.1 cm for SF determination

• Calculate L and W in units of mm and m, do not measure for these units

• Area = Length x Width, cm x cm = cm2

• All numbers must have units6CHE116

Part D: Using the Balance to Calibrate Your 10 mL Pipet

• Please use the balance carefully• DO NOT press the calibration button on the

balance• Use a small Erlenmeyer flask• The pipet size is referred to as 10 mL, but the

significant figures are 10.00 mL or 10.0 mL• Calculate volume of the pipet by using the mass

of water delivered by the pipet: D = mass / volume (see Table 1.6 on page 9)

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How to Use a Pipet

Pipetter

Pipet

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Use proper technique to prevent cutsHold pipet near end to be inserted Insert pipet into pipetter

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How to Use a Pipet• A pipet is like a calibrated straw – but never put the pipet into your

mouth1. Draw liquid into the pipet with the pipetter or rubber bulb, have

the liquid go well above the calibration mark2. Remove pipetter (or bulb) and put your index finger over the top

end to keep liquid from coming out the bottom end3. Ease up on your finger pressure so liquid can come out of the pipet

slowly until the bottom of meniscus sits exactly on the calibration mark

4. Put the bottom end of the pipet into the receiving vessel and remove your index finger so liquid drains into the vessel

5. For a TD pipet, the last drop stays in the tip of the pipet; for a TC pipet, the last drop must be pushed into the receiving vessel

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How To Calculate the Mean

• An experiment is typically done multiple times (2 or 3 times depending on time and cost)

• The mean is the average of the results

Mean = (sum of results) / (number of results)

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How to Calculate the Deviation from the Mean

Deviation = /mean – individual result/ (a (+) number)

Average Deviation = (sum of deviations)/number of deviations

The number of deviations should be the same as the number of results; use all of the data unless you know something went wrong.

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Part E and An Unknown

• Determine the density of antifreeze• Determine the density of an unknown• Work individually for the unknown liquid (lab partners must use different unknowns)

Density = mass / volumeVolume is known by pipet sizeMass is found with the lab balance

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Identify Unknown

• Use your density of the unknown liquid to determine the identity of the unknown.

• Refer to page 11 in the CHE116 packet for a list of possible substances (look for a liquid)

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