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Basic Laboratory Techniques

Let's learn to use of common, simple laboratory equipment; and let's create a hydrogen generator, too.

You'll need the following equipment: Analytical balance, 250-mL beaker, 50-mL Erlenmeyer flasks, 100-mL graduated cylinder, barometer, clamp, test tube, Bunsen burner, rubber hose, meter stick, 8-mL pipet, rubber bulb, ring stand, iron ring, wire gauze, thermometer, U tube, triangular file, 500-mL Florence flask, thistle tube, wing tip (for burner), cooling pad, rubber hosing connectors, penny, open stopper

You'll need the following materials: ice, distilled water, glycerine, glass tubing

A little background: Chemistry is a science that relies heavily on experiments. These experiments are conducted in hopes of obtaining observations that can be interpreted into results that confirm or refute the scientist’s hypothesis. There are several basic, necessary procedures and systems that every chemist must be familiar with.

The most basic of these skills is measurement. Since all measurement is uncertain, a chemist must be skilled at reading instruments and at reporting observed measurements with the proper uncertainty. A chemist must be familiar with the International System of Units (SI), as this is the preferred system of measurement in the scientific realm. The base units of the SI system are the meter for length, the gram for mass, the Kelvin for temperature, and the second for time. From these units, other units are derived; for example, the cubic decimeter is used to measure volume. The more standard, metric equivalent of the cubic decimeter is the liter. In addition, the derived unit used to measure density is the gram per milliliter.

The instrument used to measure mass is the analytical balance, which is accurate to four decimal places (.0001 g). The instrument used to measure length is the meter stick, which is accurate to 2 decimal places (.05 cm). The instrument used to measure temperature is the thermometer, which is accurate to 1 decimal places (.2 °C). The instrument used to measure volume is the graduated cylinder, which is accurate to 1 decimal place (.2 mL).

Precision is defined as the closeness of repeated measurement. Accuracy is the closeness of a measurement to the true or accepted value. Thus, it is important for a chemist to use precise measurement instruments, and to read them accurately. For example, when reading a graduated cylinder, one must be careful to read from the bottom of the curved line of liquid called the meniscus. One must also take care to eliminate error resulting from parallax view.

In addition to proper use of the instruments, which will be practiced in this lab, one must take care to learn necessary skills in the laboratory environment. For example, in this experiment, a hydrogen generator must be constructed. This will be constructed by bending and tapering hot glass tubing. This is a unique technique that must be learned properly. It will be practiced in this experiment.

Calculations involving temperature conversion and density will be made in the course of this experiment. While factor labeling is not a new technique, it is important for chemists to practice this often, as it is very important for the computational aspects of chemistry.

This experiment will serve as a refresher for many old techniques and as a practice session for several new ones.

Procedure:

1. The length of the lab book was measured and recorded using the meter stick.
2. The 100-mL graduated cylinder was filled approximately halfway with water. The volume of the water was measured and recorded. The cylinder was emptied.
3. A test tube was filled with water. This water was poured into the graduated cylinder. The volume of the water was measured and recorded. The cylinder was emptied.
4. Some ice was placed in a 250-mL beaker. Distilled water was poured over the ice. The temperature of this mixture was measured and recorded after equilibrium was reached.
5. A 250-mL beaker was set up on wire gauze and an iron ring on a ring stand. The beaker was filled about halfway with distilled water. The water was heated until it was boiling. The temperature was then measured and recorded. The barometric pressure in the room was measured and recorded.
6. A penny was weighed using the analytical balance. Its mass was measured and recorded.
7. An empty, dry 50-mL Erlenmeyer flask was weighed. Its mass was measured and recorded.
8. The temperature of approximately 40 mL of distilled water was allowed to sit for several minutes. The temperature of this water was measured and recorded.
9. 8 mL of water was pipeted into the Erlenmeyer flask using the pipet and rubber bulb. The mass of the flask containing the water was measured and recorded. This was repeated twice.
10. Glass tubing was bent using a Bunsen burner. A triangular file was used when needed to cut glass. and a ring stand, a clamp, rubber stoppers, Florence flasks, bent and straight tubing, a U tube, a thistle tube, and glycerine (used as lubricant) were used to construct this apparatus:

Observations: (numbers correspond to procedural steps)

1. Length of lab book: 11 ± 1/32 inches, 27.90 ± .05 cm
Width of lab book: 8.5 ± 1/32 inches, 21.60 ± .05 cm
2. 50.0 ± .2 mL
3. 65.0 ± .2 mL
4. 3 ± .2 °C
5. 103 ± .2 °C
Barometric pressure: 767 mm Hg
6. 3.0169 ± .0001 g
7. 36.3604 ± .0001 g
8. 25 ± .2 °C
9. Trial 1: 44.0747 ± .0001 g Trial 2: 44.3389 ± .0001 g Trial 3: 44.4731 ± .0001 g

Results:

1. Length of lab book in millimeters. (Length of lab book in centimeters multiplied by 10)
= 27.90 ± .05 cm * 10
= 279.0 mm

2. Length of lab book in meters. (Length of lab book in centimeters divided by 100)
= 27.90 ± .05 cm / 100
= .2790 m

3. Width of lab book in millimeters. (Width of lab book in centimeters multiplied by 10)
= 21.60 ± .05 cm * 10
= 216.0 mm

4. Width of lab book in meters. (Width of lab book in centimeters divided by 100)
= 21.60 ± .05 cm / 100
= .2160 m

5. Area of lab book. (Length of lab book in centimeters multiplied by width of lab book in centimeters)
= 27.90 ± .05 cm * 21.60 ± .05 cm
= 27.90 ± .18% cm * 21.60 ± .23% cm
= 602.64 ± .41% cm
= 602.64 ± 2.47 cm
= 603 ± 2 cm

6. True (corrected) temperature of boiling water. (100 °C – ((760 mm Hg – observed barometric pressure) * .037 °C/mm Hg)))
= 100 °C – ((760 mm Hg – 767 mm Hg) * .037 °C/mm Hg)
= 100 °C – (-.259 °C)
= 100.259 °C
= 100.3 °C
Using this information and the information contained in observations 4 and 5, a temperature calibration curve was constructed. It is attached to the end of this report.

7. Corrected temperature of water at room temperature. (Observed temperature plus 3 °C)
= 25 °C + 3 °C
= 28 °C

8. Mass of 8 mL of water for each of three trials. (Mass of Erlenmeyer flask and water minus mass of Erlenmeyer flask)
TRIAL ONE: 44.0747 ± .0001 g – 36.3604 ± .0001 g = 7.7143 ± .0002 g TRIAL TWO: 44.3389 ± .0001 g – 36.3604 ± .0001 g = 7.9785 ± .0002 g TRIAL THREE: 44.4731 ± .0001 g – 36.3604 ± .0001 g = 8.1127 ± .0002 g

9. Volume delivered by pipet. (Mass of water divided by density of water at said temperature)
Density of water at 28 °C = .996232 g/mL
TRIAL ONE: 7.7143 g / .996232 g/mL = 7.7435 mL TRIAL TWO: 7.9785 g / .996232 g/mL = 8.0087 mL TRIAL THREE: 8.1127 g / .996232 g/mL = 8.1434 mL

10. Mean volume delivered by pipet. (Average of results in result 9)
= (7.7435 mL + 8.0087 mL + 8.1434 mL) / 3
= 7.9652 mL

12. Average deviation from the mean. (Average of results in result 11)
= (.2217 mL + .0435 mL + .1782 mL) / 3
= .1478 mL

13. Volume delivered by pipet using proper notation. (Mean volume delivered by pipet ± average deviation from the mean)
= 7.9652 ± .1478 mL
= 8.0 ± .1 mL

14. Hydrogen generator, final product.
This is a picture of the end result of the glass work and assembly.

Discussion: There are several sources of error in this experiment. For example, when weighing the water discharged by the pipet, some of the water could have evaporated. If anything caused the countertop to move even slightly, the reading on the balance could have been caused to shift between incorrect readings and correct readings. When bending the tubing, overheating or underheating the tubing could have caused the bend to be rough and imperfect. Using the triangular file improperly could have also caused imperfections in the tubing. Not allowing the icewater mixture to come to equilibrium would have caused an incorrect reading on the thermometer, causing the calibration curve to be incorrect.

The theory associated with this experiment involves density. Density is mass over volume. Since the volume of a liquid or gas is contingent upon temperature, it can be deduced that density depends on temperature. Liquids can expand when heated or shrink when cooled because the motion of the molecules in the liquid is increased or decreased accordingly. The motion of molecules increases as kinetic energy (temperature) is increased, causing the volume to increase. The motion of molecules decreases as temperature decreases, causing a drop in volume.

Since this was a skill-building exercise, the ramifications are chiefly comprised of learning new techniques. This experiment served as practice for future experiments. In addition, equipment for future use was prepared during this experiment.

Questions:

1. 5’9” = 69 inches; 69 in (1 meter / 39.37 inches) = 1.75 m = 175 cm
160 lb (1 kg / 2.2 lbs) = 72.7 kg

2. 100 °C – ((760 mm Hg – 698.5 mm Hg) * .037 °C/mm Hg) = 97.7 °C

3. Density of water at 19°C = .998405 g/mL
Volume = mass/density
9.97 g / .998405 g/mL = 9.99 mL

4. Mean volume: (10.02 mL + 10.12 mL + 10.08 mL + 10.06 mL) / 4 = 10.07 mL
Individual deviations, in order: .05 mL, .05 mL, .01 mL, .01 mL
Average deviation: (.05 mL + .05 mL + .01 mL +.01 mL) / 4 = .03 mL

5. 121 mg = .121 g
8.203 g + .121 g = 8.324 g

6. a. See second attached graph.
b. It appears to be near 5°C.
c. °C = 5/9(°F-32); 5/9(40-32) = 4.45 °C

Conclusion: The purpose of this experiment was achieved well. The use of common, simple laboratory equipment was learned. A hydrogen generator was created for use in a future experiment.