1. Experiment 1 Basic Laboratory Techniques Parts A, D, E, and an Unknown
(work in groups of 2)
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2. 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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3. Calibration Scales
Know how to read the calibration marks on a piece of calibrated equipment and determine:
the correct number of significant figures
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 balance
Part E uses a pipet and balance
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4. CHE116
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 size
Laboratory balance: ±0.01g or ±0.001g
(check readout)
Pipet: only one calibration line, ± depends on quality of pipet
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5. Reading A Calibration Scale
In General:
Find difference between numbered tick marks
Use the un-numbered tick marks between the two numbered marks to count the number of jumps from one numbered mark to the other
Determine what each un-numbered mark is worth
Estimate one digit beyond the un-numbered tick marks (this is the last significant digit for the measurement)
Read the measurement, using the correct number of significant figures
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6. 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 units
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7. 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 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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8. How to Use a Pipet
Pipet
Pipetter
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9. Use proper technique to prevent cuts
Hold pipet near end to be inserted
Insert pipet into pipetter
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10. How to Use a Pipet
A pipet is like a calibrated straw – but never put the pipet into your mouth
Draw liquid into the pipet with the pipetter or rubber bulb, have the liquid go well above the calibration mark
Remove pipetter (or bulb) and put your index finger over the top end to keep liquid from coming out the bottom end
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
Put the bottom end of the pipet into the receiving vessel and remove your index finger so liquid drains into the vessel
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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11. 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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12. 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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13. 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 / volume
Volume is known by pipet size
Mass is found with the lab balance
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14. 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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