Experiment 1 Basic Laboratory Techniques Parts A, D, E, and an Unknown (work in groups of 2) CHE116

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) CHE116

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 CHE116

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 CHE116

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 CHE116

Part A: The Meter Stick Use your lab book as an 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 CHE116

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 beaker or 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) CHE116

How to Use a Pipet Pipet Pipetter CHE116

Use proper technique to prevent cuts Hold pipet near end to be inserted Insert pipet into pipetter CHE116

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 CHE116

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) CHE116

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. CHE116

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 Part D Mass is found with the lab balance CHE116

Identify Unknown Use your density of the unknown liquid to determine the identity of the unknown. Refer to page 9 in the CHE116 packet for a list of possible substances (look for a liquid, m.p. less than room temp.) CHE116