General Chemistry Laboratory I Manual, Lab Reports of Chemistry

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GENERAL CHEMISTRY

LABORATORY I

MANUAL

Fall Semester

Contents

• Experiment 1 Measurements and Density Laboratory Equipments i
• Experiment 2 The Stoichiometry of a Reaction
• Experiment 3 Titration of Acids and Bases
• Experiment 4 Oxidation – Reduction Titration
• Experiment 5 Quantitative Analysis Based on Gas Properties
• Experiment 6 Thermochemistry: The Heat of Reaction
• Experiment 7 Group I: The Soluble Group
• Experiment 8 Gravimetric Analysis
• Scores of the General Chemistry Laboratory I Experiments

ii

What is Meniscus Point and how to read it?

VOLUMETRIC FLASK (BALONJOJE)

Volumetric flasks are used for measuring very precise and accurate amount of a liquid and is used for such when the amount is too much for pipette or burette. They are also used for solution preparation.

PIPETTE (PİPET)

Pipette is a glass tube used for the delivery of a measured quantity of liquids. There are two kind of pipettes: a) Graduated (Measuring) Pipette : has many graduated marks, much like a graduated cylinder that can deliver moderately accurate volumes (left picture) b) Volumetric (Transfer) Pipette : a kind with a bulbous middle section that has a single mark for the quantitative delivery of a single volume of liquid each time (middle and right picture)

SUCTION DEVICE (PUAR)

A suction device or rubber bulb is a device to place on top of pipettes for generation of vacuum to transfer known volume of liquid, usually from one container to another. Meniscus point occurs when liquid molecules adheres themselves onto the walls of the glassware. This phenomenon is known as adhesion. Always read the value right at the bottom of the meniscus 24 mL not 25 mL

iii

Use of a suction device with a pipette:

PASTEUR PIPETTE (PASTÖR PİPETİ)

Pasteur pipette (or medicine dropper) is a plastic or glass pipette used to transfer small amounts of liquids, but are not graduated or calibrated for any particular volume.

STAND (STAND)

A metal rod attached to a heavy metal base. The heavy base keeps the stand stable, and the vertical metal rod allows for easy height adjustment of the iron ring/clamp.

BURETTE (BÜRET)

Burette is a vertical cylindircal piece of laboratory glassware with a volumetric graduation on its full length and a stopcock on the bottom. It is used to dispense known amounts of a liquid reagent in a titration experiment. Before using the suction device deflate the air inside by pressing button A. Then connect the suction device on to a pipette. Press the button S for suction. Measure desired amount of liquid with pipette by taking meniscus point into account. While emptying use button E

v

WATCH GLASS (SAAT CAMI)

Watch glass is used to allow crystals to dry after they have been filtered. They can be used as an evaporating surface or to cover a beaker that can be heated to very high temperatures.

SEPARATORY FUNNEL (AYIRMA HUNİSİ)

Separatory funnel is used in liquid-liquid extractions to separate the components of a mixture between two immiscible solvent phases of different densities. It is fixed on a stand by a ring support.

OVEN (ETÜV)

An oven is an enclosed chamber in which heat is produced to dry chemicals or laboratory equipments.

EVAPORATING DISH (BUHARLAŞTIRMA KROZESİ)

The evaporating dishes are made of porcelain or ceramic material to heat and evaporate solutions to dryness.

vi

ROUND-BOTTOM FLASK (BALON)

Round bottom flasks are used for heating or boiling of a liquid, in distillation procedures and to carry out chemical reactions. Their two or three-necked versions are also available and usually more suitable for carrying out reactions.

TEST TUBE (TEST TÜP)

Test tubes are used as containers for solids and liquids to perform quick tests for properties such as solubility, effect of heat, etc. They can also be used as centrifuge tubes when a separation of solid and liquid is necessary.

TEST TUBE RACK (TÜPLÜK)

The test tube racks provide places to hold the test tubes vertical so that chemicals are not spilled out.

TEST TUBE BRUSH (TÜP YIKAMA FIRÇASI)

Test tube brush is a long and narrow equipment to clean the inside of glassware particularly test tubes.

THERMOMETER (TERMOMETRE)

A thermometer is a device used to measure temperatures or temperature changes.

viii

BUNSEN BURNER (BEK ALEVİ)

Bunsen burner is a used for heating when no flammable material is present. The burner can be regulated by changing the air and gas mixture.

WASH BOTTLE (PİSET)

Washbottles usually contains distilled water or acetone and makes for a convenient method to wash out lab glasswares.

STOPPER (TIPA)

Stoppers are used to close flasks and test tubes to protect from the environment.

FUME HOODS (ÇEKER OCAK)

The fume hoods protect laboratory workers from fumes and potentially dangerous chemicals reactions by continuously vacuuming air out of the lab and providing a glass shield.

ix DISPOSAL OF CHEMICALS and CLEANING-UP THE GLASSWARE If material solid, use solid waste. If it is liquid, determine whether the substance is organic or inorganic then use the related waste. Use acetone to dissolve organic material. For both organic and inorganic materials, they require distilled water to be cleaned up properly. Use brushes to clean glassware if necessary.

Experiment 1: Measurement and Density 11 Random errors are more related to experimental uncertainty than to accuracy. Their sources cannot be identified and are beyond our control. They also tend to fluctuate in a random fashion about a measured value. One of our main tasks in designing and performing experiments is to reduce or eliminate the effects of systematic error. In this way, only the cumulative effect of the random errors remains, and this may be estimated in terms of precision. PRECISION The key to significance in experimental measurements is repetition. Only with repeated measurements of density, concentration, or other quantities can the experimenter have some confidence in the significance of measurements. Only if a measured quantity can be reproduced repeatedly can the experimenter have that confidence. Precision is a quantitative measure of the reproducibility of experimental measurements. It is how well repeated measurements of the same quantity agree with one another. Precision is frequently measured in terms of the average deviation, which is determined by the following process:

1. From series of measurements (three or more) determine the average value. 2. For each measurement determine its deviation from the average value. 3. Determine the average of the deviations without regard to sign. In order to make the measurements of precision more useful, the average deviations are put on a percentage basis by determining the relative average deviation. This is the average deviation divided by the average value and multiplied by 100 %. Example: In the determination of concentration of an unknown acid by titration with standard base, four measurements were made: 0.1025 M, 0.1018 M, 0.1020 M, and 0.1024 M. a) Compute the average value and the average deviation. b) Assuming the accepted value of the unknown acid molarity is 0.1014 M, determine relative error of the experiment. Solution: a) The average value is computed by summing the four measurements and dividing by four. This yields an average value of 0.1022 M.

Experiment 1: Measurement and Density 12 The individual deviations of each measurement from the average value are 0.0003 (0.1025), 0.0004 (0.1018), 0.0002 (0.1020), and 0.0002 (0.1024). The sum of the four deviations, 0.0011, divided by four yields the average deviation, 0.00028. Since this deviation represents an uncertainty in the measurements, the molarity of the unknown acid is not precisely 0.1022 M, but ranges from 0.1019 M to 0.1025 M and should, therefore, be reported with the average deviation included, that is, 0.1022 ± 0.0003 M. In the example, the relative average deviation is A relative average deviation of 0.27% or better (that is, smaller) is a typical expected precision value for an acid-base titration. In general, however, the precision of an experiment varies with the technique and/or apparatus used. Number of variables built into the method or design of the experiment can affect its precision. b) Since the error is the difference between the measured value and accepted value, in this case it is 0.1022 – 0.1014 = + 0.0008. From this error, the % error is calculated as

Experiment 1: Measurement and Density 14 The relative average deviation in the volume is found by dividing average deviation to average volume and multiplying it by 100 % (0.02 ml/10.00 ml) x100 % = 0.2 %. The density is, therefore, is obtained by dividing the mass of solution to the volume 10.713 g/10.00 mL = 1.071 g/mL The relative average deviation is found by addition of the deviations in both mass and volume measurements 0.07% + 0.2% = 0.3%. The absolute deviation of the density is (0.3% /100%)(1.071 g/mL) = 0.003 g/mL. Thus, we would report 1.071 ± 0.003 g/mL as the density. SIGNIFICANT FIGURES Associated with the evaluation of experimental data is an understanding of the extent to which the numbers in measured quantities are significant. For example, the mass of an object can be measured on two different balances, one a top-leading balance sensitive to the nearest 0.001 g and another a triple-beam balance sensitive to the nearest 0.1 g. These balances have a different uncertainty and precision. Top-loading Balance Triple Beam Balance Quantity 54.236 g 54.2 g Uncertainty ± .002 g ± 0.1 g Measured mass 54.236 ± 0.002 g 54.2 ± 0.1 g Precision high (2 parts in 54.236) low (1 part in 542)

Experiment 1: Measurement and Density 15 On the top loading balance with high precision, five significant figures are available. On the triple-beam balance only three figures are significant. Thus, significant figures are the numbers about which we have some knowledge. If no information is available regarding the uncertainty of the measuring device, one may assume that all recorded figures are significant with an uncertainty of about one unit in the last digit. Zeros are significant if they are part of the measured quantity, but not if they are used to locate the decimal place. Thus, 62.070 has five significant figures while 0.0070 has only two (the first three zeros only locate the decimal place). In calculations involving measured quantities with different numbers of significant figures, the result must be evaluated carefully with respect to the number of digits retained. In addition, or subtraction, the number of digits retained is based on the least precise quantity. For instance, consider the following summation of masses. Here the result should be rounded to 149.2 g since the least precise mass is known only to the first decimal place. In multiplication and division, the number of significant figures retained in a result is equal to the number in the least reliably known factor in the computation. For example, in the determination of the density of an object, the measured mass is 54.723 g while the measured volume is 16.7 mL. The density of the object is 54.723 g/16.7 mL = 3.28 g/mL. Note that only three significant figures can be retained. When a number is rounded, the last figure retained is increased by one unit if the one dropped is more than five and decreased by one unit if the one dropped is less than five. Examples: a) 3.276 → 3.28 b) 149.74 → 149.7 c) 5.45 → 5. As we have emphasized, chemistry is very much an experimental science in which careful and accurate measurements are the very essence of meaningful experimentation. It is therefore, essential for the beginner student of chemistry to learn how scientific measurements are carried out properly using common measuring instruments. Further, it is equally important

Experiment 1: Measurement and Density 17

MATERIALS CHEMICALS

50 mL beaker Distilled water 25 mL pipette Salt Solution 25 mL graduated cylinder Suction Device Balance Metal Bar Ruler PROCEDURE PART I: MEASUREMENTS A. Mass Measurements After balance instruction, you will be assigned to select a balance for use during the experiment.

1. Zero the balance.
2. Measure the mass of a clean dry 50.00-ml beaker to the nearest ±0.001 g.
3. Record, in ink, your observation directly into the lab notebook/data sheet.
4. Remove the beaker from the pan. Again, zero the balance.
5. Weigh the same beaker as before (step 2) and record the result.
6. Repeat the steps 4 and 5 one more time.
7. From the three measurements, calculate the average mass of the beaker. B. Volume Measurements Use of a pipet: In order to accurately measure a liquid volume using a pipette, we must consider several things. Most volumetric pipets are designed to deliver rather than contained the specified volume. Thus, a small amount of liquid remains in the tip of the pipet after transfer of liquid. This kind of pipet is marked with the letters ‘‘TD’’ somewhere on the barrel of the calibration line. Also, for purposed of safety, never pipet by mouth ; that is, never use your mouth to draw liquid into the pipet. Always use a suction device/bulb (Figure 1). A: Air valve expels air from bulb. S: Suction valve draws solution into the pipet. E: Empty valve drains solution from the pipet. Figure 1. Suction device/bulb. A S E Airvalve Suctionvalve Emptyvalve

Experiment 1: Measurement and Density 18 Use a clean, and dry, 20.00 or 25.00-ml pipet. Rinse the pipette several times with small portions of the liquid to be transferred. To measure the desired volume, a volume of liquid greater than that to be measured is needed in order to keep the pipette tip under the liquid surface while filling. Before using the suction device, deflate the air inside by pressing button A. Then connect the suction device on to pipette. Immerse the tip of the pipette inside the liquid, but not touch the bottom of the container (a chipped tip causes error) and hold it vertically. Press the button S for suction. Measure desired amount of liquid with pipette by taking meniscus point into account. While emptying use button E.

1. Measure the temperature in the laboratory. Your instructor will provide you with the density of water at this temperature.
2. Use the same 50.00-ml beaker from Section A for determining the mass of each liquid of water. Rather than weighing the empty beaker, the average mass of the beaker determined in Section A will be used as the mass of the dry beaker.
3. Measure 20.00 or 25.00-ml of water (depending on the size of pipette available) into the 50.00-ml beaker.
4. Record the volume of water measured with the pipette to the appropriate number of significant figures.
5. Record the number of significant figures in the volume measurement.
6. Weigh the beaker and water to the nearest mg (±0.001g).
7. Calculate the mass of water in the beaker.
8. Use the mass and density of water to determine the volume of water measured.
9. Repeat steps 3-8 using a 25.00-ml graduated cylinder and 50-ml beaker instead of the pipet to measure the 20.00 or 25.00 ml of water. PART II: DENSITY A. Density of A Metal Bar Mass Measurement of A Metal Bar NOTE: Use the same metal bar for all trials.
10. Zero your balance. Weigh a metal bar on a balance to the nearest mg (±0.001g) and record its value. Repeat step 1 twice. Do not allow the first measurement that you obtain to influence subsequent measurements that you take. Each time you weigh, make sure you zero the balance before proceeding. Determine the volume of the metal bar by each of the following methods, making at least 3 measurements by each method. Do not allow the first measurement to influence the