CHEMISTRY 3452

QUANTITATIVE TECHNIQUES

Student Name: __________________________

CHEMISTRY 3452

LABORATORY SYLLABUS

Week of: Lab # Lab Title

Sept 8^th 1 Check-in / Use of Lab Equipment

Sept 15^th 2 Gravimetric Determination of Calcium

Sept 22^nd 3 Determination of KHP

Sept 29^th 4 Determination of Acid in Vinegar

Oct 6^th 5 Determination of Sodium Carbonate

Oct 13^th Quiz (Labs 1-5)

Oct 20^th 6 Determination of Water Hardness

Oct 27^th 7 Potentiometric Determination of KHP

Nov 3^rd 8 Determination of Fe by KMnO4

Nov 10^th 9 Determination of Iodine using Iodate

Nov 17^th 10 To be determined

Nov 24^th Quiz (Labs 6-10) / Check-out

TA’s: Michelle Garza (ma0019@unt.edu) - Mon., Room 304, 1:00 – 4:50 pm

Wed., Room 304, 5:00 – 8:50 pm

Oscar Ojeda (ouo0001@unt.edu) - Tues., Room 304, 1:00 – 4:50 pm
There will be a brief discussion of each lab at the beginning of the period. The student will be expected to have read the lab manual before coming to class, since the discussion will focus on why, not how, the lab is done.

Materials

Lab Manual

Lab Notebook

Black or Blue Ink Pen

Safety Goggles

Grading

The lab grade will be calculated as follows:

laboratory reports 70%

laboratory notebook 5%

2 Quizzes 20%

TA Evaluation 5%

Notebooks will be inspected at unannounced times during the semester, and graded according to completeness and organization. The "TA Evaluation" portion of your lab grade will reflect your attitude, preparedness, and safety-consciousness during lab.

Lab Reports

The last page of each lab handout is the lab report sheet, on which you will report your lab results. This information will come directly from your lab notebook (see below), and any blanks on the report must be filled in or explained. The report sheets are due at the beginning of the lab period immediately following the completion of the lab. Ten points will be automatically deducted from late lab reports, and no lab will be accepted more than two weeks after the date due.

Lab Notebook

All students will use a lab notebook to record all data obtained in this lab. The notebook must be one in which the pages are permanently attached -- loose leaf notebooks are not acceptable. Recording data on scratch paper, paper towels, etc. before transfer to the notebook is expressly forbidden. Any student found using such scratch paper will have 10 points automatically deducted from their lab grade for that lab and the scratch paper will be discarded.

Your lab notebook must always be up-to-date. Since you will not be recording data anywhere else, this should not be a problem. The TA will check notebooks during the lab period, and anyone found with an incomplete notebook for a previous lab will have their "Notebook" grade lowered by 5%.

The notebook will contain the following information in a clear, easy-to-read, understandable manner:

A) A brief description of experimental procedure, or a flow chart.

(This should be written in advance of the lab period, and is for your own use as an organizational aid as you perform the lab.)

B) All raw data. (Preferably recorded in data tables for easy reference.)

C) At least one example of every calculation.

D) All conclusions (such as composition of unknown), and any reasons why lab results are not up to expectations (such as: "neighbor's experiment blew up all

over my reaction vessel").

Results should be in tabular form, well labeled, and easy to understand by someone not familiar with your notebook.

E) If your notebook is illegible, all conclusions will be assumed to be incorrect and
graded accordingly.

Leave an empty page at the beginning of your notebook for a "Table of Contents". Fill it in as you complete each experiment.

Lab Clothing and Eye Protection

Eye protection is required by state law for everyone in a laboratory, regardless of whether they are actually doing anything or not. Goggles are strongly recommended since they provide more adequate splash protection. Any person who refuses to wear eye protection will leave the laboratory and take an automatic "0" for that lab exercise. If you do not have a pair of goggles, you may purchase them in Masters Hall Room 210.

We will be using large quantities of acids and bases this semester. These chemicals tend to dissolve clothing (and flesh) with which they come into contact. It is advisable to consider any garment worn to lab as potentially disposable -- dress accordingly. Also: since most liquids tend to follow gravity after a spill, long pants and closed shoes are recommended.

Exercise caution when touching anything. It is especially unwise to sit or lean on the lab benches. If an acid or base has been spilled and left to evaporate, it will have left a residue that could easily install air conditioning in any clothing it contacts.

Graphing

Several experiments in this lab will require the use of graphical methods of data analysis. When graphing continuous data (including most experimental results), a smooth curve should be drawn through the data points so that there are an equal number of points above and below the line. This is essentially a method of determining the average value of a function along the curve. A few other points to remember when graphing:

A) Use as much of the graph paper as possible. Your graphs will be more legible
and more accurate.

B) If more than one curve is shown on the same sheet of paper, use
different colored lines, different symbols for the data points (circles and stars, for
example), or dotted versus continuous lines to differentiate the data sets. Make
certain the difference is obvious, and provide a key to identify which is which.

C) The x- and y-axes need not start at zero. Use only the parts of the axes which
contain the domain and range of your data.

The following graphs illustrate these points, with the graphs on the left showing good techniques and those on the right showing poor techniques. 1A and 1B show the benefit of graphing only that portion of the graph that is of interest. Graphs 2A and 2B illustrate the best way to draw a line through a series of data points (calculators can do this by a least squares program). Graphs 3A and 3B illustrate why you should use reasonable scales on both axes.

Place holder for Figure 1 to 3 A &B.
Place holder for lab report example (3 pages)
INTRODUCTION TO USE OF LAB EQUIPMENT

Purpose: To avoid costly and time-consuming mistakes

Objective: To learn the correct use of commonly used equipment

Equipment: All

PROCEDURE:

Read the following information and the corresponding sections in the text. Answer the questions at the end of this experiment. The answer sheet must be turned in before you can begin the exercise. If you have any questions, please ask; it will save you time later.

You were most likely exposed to the following pieces of equipment and the rules for their use during freshman or organic chemistry. However, in quantitative analysis, we are interested in exact quantities, and so we are much more dependent on accurate measuring devices and techniques. Two or three extra drops or a careless fingerprint can affect your grade. Our goal this semester is to obtain results within 1 or 2% of the correct value -- anything over 5% will not be considered passing work.

Glassware

In most cases, it is not necessary to dry glassware before use. The most common ways to dry glassware will, in fact, contaminate the glass. Paper towels can introduce significant contamination into a sample, and should never be allowed to come into contact with the primary surface of a container. Compressed air contains dust and oil from the compressor. Glassware should only be dried, then, when water must be excluded.

Wash all glassware well and rinse with several small aliquots of distilled water instead of one large aliquot.

Volumetric glassware (burets, pipets, volumetric flasks, etc.) is not designed to withstand heating. The glass may break, and it will almost certainly distort, altering the volume to an unknown degree. Never place a ground glass stopper on the tabletop. It will pick up contaminants, and could easily roll off the table and break. Instead, remove a stopper from a bottle with the knuckles of your first two fingers, so that the ground glass portion sticks away from your palm. This allows the use of both hands for subsequent manipulations, and minimizes the chances for contamination.

Reagents

The best rule here is the Golden Rule: "Do unto others as you would have them do unto you". Your results and your grade will depend on the care with which everyone else in the class treats the common reagents, and their results will depend on you.

1) Never put anything back into a common reagent container unless specifically instructed to do so by the lab instructor. A dirty spatula can spoil every batch of material taken from that bottle.

2) Place approximately what you will need in a beaker, watch glass, or on weighing paper. If you have excess, share it with a (trusting) buddy or throw it away. Do not return the excess to the reagent container.

3) When removing the tops from reagent containers, never allow the stopper to become contaminated (see above). Always replace all stoppers immediately after use, to keep dust and other contamination from falling into the container.

Pipets

There are several types of pipets in use today. Each type requires a specific method of use, and incorrect use can result in up to 10% error for that measurement. If you are not sure what type of pipet you have, then, ask. Your grade will depend on it.

1) Never pipet by mouth. This is more than a rule -- it is the law. Also, it can contaminate your sample. Always use a pipet bulb. If you are unsure how to use a pipet bulb effectively, ask the TA for a demonstration.

2) Always pre-rinse the pipet with the solution you are about to measure, and then discard the rinse solution. This removes any water adhering to pipet walls, and prevents dilution of the solution inside the pipet.

3) The pipet you are using is marked at the top with a number, representing the maximum capacity of the pipet, and the initials "TD" or "TC". "TD" stands for "to deliver", and the pipet delivers the stated volume by gravity alone -- do not try to remove the last drop which remains in the tip after emptying. "TC" stands for "to contain", and the stated volume includes that final little drop. Use a pipet bulb to blow it out into your reaction container.

The following types of pipets will be used in this lab:

1) Volumetric (sometimes called a "transfer pipet"): Does not have graduations. It is designed to deliver exactly the stated volume when filled to the etched line. Volumetric pipets are always "TD" pipets.

2) Mohr (also called a measuring pipet): Neither TD nor TC, these should only be used to measure volumes which do not require complete emptying of the pipet.

3) Serological: May be either TD or TC. These pipets have graduations all the way to the tip of the pipet, so be certain which kind you are working with before you start.

Burets

Burets can be tricky. A buret is calibrated to show the amount of solution that has been dispensed, not the amount of solution left in the buret. Be very careful when reading a buret, and if you are at all uncertain, ask the TA for a demonstration.

1) Fill the buret with deionized water to see that it is working correctly. There should be no leakage when the stopcock is closed, and there should be a continuous stream coming out the tip when the stopcock is fully open. If this isn't the case, alert the TA.

2) Always pre-rinse the buret with the solution to be measured. Place approximately 5 mL of the solution in the buret with the stopcock closed, and tilt and rotate the buret so that the solution contacts the entire inside surface. Open the stopcock to allow the solution to exit through the tip of the buret, discarding this solution, then close the stopcock and repeat two more times. Finally, place the buret in the buret holder and fill the buret with the solution to be measured.

3) Open the stopcock completely for a second or two to allow the solution to flow. This flushes any air bubbles out of the tip. Be sure there are no air bubbles left in the tip of the buret before beginning the titration.

4) The buret need not be filled exactly to 0.00, but the initial reading, whatever it is, must be recorded accurately before a titration is begun.

5) A small, but significant, amount of solution will adhere to the walls of the buret after each addition. Wait approximately one minute after your final addition before taking your final reading.

6) Read the buret as accurately as possible. At the beginning of the semester, you can probably read to an accuracy of + 0.04 mL. This should improve to + 0.02 mL by the end of the semester.

Analytical Balance

The analytical balance is one of the most sensitive and expensive instruments you will use this semester. Replacement cost of each balance is around $2000. It is therefore extremely important to use the balance correctly and carefully, to avoid any possible damage. Since every experiment this semester involves the accurate weighing of at least one compound, proper use of the balance will also affect your results.

1) The balance should be in the "off" position when not in use, and all the weights should be set to "zero".

2) Never place a chemical directly on the balance pan. Always use weighing paper or a small container for weighing.

3) Always have the balance in the "off" position when adding or removing anything from the balance pan.

4) The balance doors should be completely closed before taking a final weight, since air currents will affect your readings.

5) Use the preweigh (partial release) position to obtain an approximate weight.

6) Only after the approximate weight has been determined and set should you turn the balance to the full release position. This will avoid any undo stress on the mechanical components of the balance.

7) Always turn the balance off and set the weights back to zero when you are through with the balance.

8) Keep the balance area clean at all times to prevent corrosion of the balance. Be sure to clean up any spill in the vicinity of the balance.

INTRODUCTION TO USE OF LAB EQUIPMENT QUESTION SHEET

NAME_______________________________

1) Why is it not necessary to dry glassware before use?

2) How does one hold the ground glass stopper from a volumetric flask or reagent bottle?

3) What should you do with excess chemicals that you have taken to your desk?

4) What are two good reasons why you should never pipet by mouth?

5) What do the initials "TD" and "TC" near the tip of a pipet stand for?

6) What volume of solution is necessary to rinse out a buret?

7) Why should you drain the solution from a buret slowly, or wait after draining, before taking a reading?

8) To how many decimal places should one read a buret?

9) What are the proper settings on an analytical balance when the balance is not in use?

10) What is the purpose of the partial release position on an analytical balance?

GRAVIMETRIC DETERMINATION OF CALCIUM

AS CALCIUM OXALATE MONOHYDRATE

Purpose: To determine the concentration of Ca⁺² in an unknown

solution by gravimetric analysis.

Objective: To become familiar with gravimetric analysis and

precipitation from homogeneous solution.

Equipment: Filter crucibles

Key Points: Precipitation from homogenous solution.

PROCEDURE:

Clean a fritted filter crucible by heating it gently in a solution made by adding approximately 5 mL of concentrated HNO₃ and 1 mL of 3% H₂O₂ to about 150 mL of water. Allow the crucible to heat gently for about 15 minutes. Rinse the crucible with large volumes of destilled water and place in the oven to dry for approximately 2 hours. Cool the clean, dry crucible in the desicooler.

Prepare an ammonium oxalate solution by adding approximately 4 grams of ammonium oxalate and 2.5 mL of concentrated HCl to 100 mL of deionized water.

Precipitation of Calcium Oxalate

Obtain approximately 40 ml of the unknown from the TA. Pipet 25.00 ml of the unknown into a 400 ml beaker. Add 75 ml of 0.1M HCl and 5 drops of methyl red indicator. (The 0.1M HCl can be made by adding 1 ml of concentrated HCl to 100 ml of water.)

Add 25 to 30 ml of the oxalate solution to the beaker and mix well. Add about 20 grams of solid urea to the solution. Cover with a watch glass and bring to a gentle boil. Boil the solution until the methyl red indicator turns from red to yellow. Continue boiling for 15 minutes after the solution has changed color.

Weigh the cooled, clean dry fritted glass crucible and set up the suction filtration. Filter the still hot solution. Use cold water to rinse the beaker of all remaining solid. (Use approximately 5 mL additions.)

After the beaker has been thoroughly rinsed, add 10 ml of cold destilled water to the crucible to complete the washing of the precipitate. After all the solution has been filtered, continue the suction for approximately 5 minutes to partially dry the crystals of CaC₂0₄ H₂O.

Place the filter crucible with the calcium oxalate monohydrate crystals in the oven for about 2 hours, if short of time, cover with a watch glass and dry it next lab period. Allow to cool in the desicooler. Weigh. Based upon the weight of calcium oxalate monohydrate obtained, determine the molar concentration of Ca in the original unknown.

(If time does not allow for the drying of the crystals for 2 hours during this lab period, place the crystals in the desicooler and dry for two hours during the next lab period. Be sure to keep the crucible from touching the calcium chloride used in the desicooler.)

REMEMBER --- Do not heat the solution too quickly or it may bump and cause some of the solution to boil over onto the top of the lab bench.

Do not handle the crucible with your fingers any more

than is absolutely essential to keep from adding

additional weight from the oil on your fingers.

GRAVIMETRIC DETERMINATION OF CALCIUM REPORT SHEET

Name ______________________

Unknown # _________________

Volume of Unknown _________

Weight of precipitate _________________

Molarity of Ca⁺² ___________ (to 4 places)

in original solution

TITRIMETRIC DETERMINATION OF KHP

Purpose: To determine the percent potassium hydrogen phthalate (KHP) in an unknown.

Objective: To become proficient in titration and calculations involved in titrimetric procedures.

Equipment: Pipets, burets, analytical balance

Key Points: Titration Techniques and Significant Figures

PROCEDURE:

The KHP unknown and the KHP Primary Standard Grade Known must be dried at 110^oC for at least one hour before use. Be sure to label everything well.

For the unknown, remove the plastic top and set the vial upright in a covered beaker. Remember to record your unknown number.

Preparation of NaOH:

Prepare a sodium hydroxide solution by adding approximately 1.8 grams of solid NaOH to a 1 liter brown bottle half-filled with distilled water. Mix well. Dilute until the bottle is about 9/10 full and mix well.

Rinse a buret several times with the NaOH solution as instructed and fill the buret with the NaOH solution. Make sure there are no air bubbles remaining in the tip of the buret.

Weigh approximately 0.4 grams of the Primary Standard Grade KHP (100%) into a 250 ml erlenmeyer flask. Record the weight to 4 places. Dissolve the solid in approximately 75 ml of water and add 3 or 4 drops of phenolphthalein indicator. The solution should be colorless. If it is not, then please seek assistance before proceeding.

Titrate the sample with NaOH until one drop of NaOH produces a faint pink color which persists for at least 30 seconds in a well stirred solution. The appearance of the pink color indicates the end point. The solution will continue to get darker pink and eventually red as you add additional NaOH so you must stop at the first sign of pink. It is easy to see if you place a light colored piece of paper underneath the titration flask.

Repeat the titration with two additional samples of the Primary Standard Grade KHP making appropriate changes in sample size. (For instance: if a 0.4 gram KHP sample takes over 20 ml of solution then you need to take a smaller sample for the next two. If a 0.4 gram sample takes less than 7.5 ml of solution then you should take a larger sample.)

Using the volume of NaOH, the mass of the KHP, and the following equation, determine the concentration of the NaOH.

NaOH + KHP ------> H₂O + NaKP

Determination of an Unknown:

Weigh out approximately 0.5 gram of the unknown into a 250 ml erlenmeyer flask and add 75 ml of water and 3 or 4 drops of phenolphthalein. Titrate the unknown in the same manner as with the primary standard grade KHP.

Repeat with two additional samples of the unknown adjusting sample size as needed.

Determine the % KHP in the unknown.

REMEMBER --- Titrate to the first permanent pink. If it turns too red then you have gone too far.

NOTE --- Save the NaOH solution and return the remaining unknown KHP for use in the potentiometric laboratory exercise.

TITRIMETRIC DETERMINATION OF KHP REPORT SHEET

Name ________________________

NaOH Standardization Unknown # _________

# Weight KHP Volume NaOH M of NaOH

1 __________ ___________ _________

2 __________ ___________ _________

3 __________ ___________ _________

mean M _________

% RSD _________

Determination of Unknown Unknown # _________

# Weigh Volume NaOH % KHP

1 __________ ___________ _________

2 __________ ___________ _________

3 __________ ___________ _________

% KHP mean _________

% RSD _________

Selection of an Appropriate Acid-Base Indicator

Determination of Acetic Acid in Vinegar

Principles

The endpoint of an acid-base titration can be conveniently determined potentiometrically using a pH meter, or visually using an acid-base indicator. Potentiometric endpoint determination involves measuring the pH of the solution after each incremental addition of titrant, and then constructing a pH titration curve by plotting the measured pH of the solution after each incremental addition of titrant (which in this case is NaOH solution). The endpoint is the infection point of the "S-shaped" titration curve. Alternatively, the endpoint can be determined by selecting an appropriate acid-base indicator having a visual color change. The color change arises because the protonated and unprotonated forms of the indicator have different colors. For example, methyl red is red at a pH < 4.8 and yellow at a pH > 6. (NOTE: Pages 294 - 296 of our textbook, Quantitative Chemical Analysis, 4 edition, by Daniel C. Harris discusses indicators and indicator selection in greater detail.)

One of the purposes of this particular laboratory experiment will be to study acid-base indicators in greater detail, and to select an appropriate indicator for the quantitative determination of vinegar in an unknown liquid solution. Vinegar consists primarily of a 4 to 6% solution of acetic acid. It also contains small amounts of other acidic components, but it is customary to report the total acid content as percent (weight-volume) acetic acid

(HC₂H₃O₂). The acid content in vinegar can be determined by titration with 0.1 N NaOH. Because acetic acid is a weak acid (K_A = 1.75 x 10^-5), the equivalence point pH will be near 9. The indicators that will be examined include methyl red (red to yellow), bromocresol green (yellow to blue), phenolphthalein (colorless to faint pink), methyl orange (red to yellow) and alizarin yellow (and yellow to orange-red). The pH range for each indicator is listed in the textbook.

Because the acid concentration is so high in vinegar, it is convenient to dilute the sample and employ aliquots for the titration (note 1). Do not neglect the dilution factor in your calculation.

Directions

Use your NaOH solution that has already been standardised against the primary standard KHP.

Obtain approximately 80 ml of the unknown from your TA. Rinse/clean pipet with small amount of unknown then transfer 25 ml. of the vinegar sample to a 250 ml volumetric flask, using a volumetric pipet. Dilute to the mark with distilled H₂O. Mix thoroughly. Pipet 50-ml aliquots into 250-ml Erlenmeyer flasks, and add 50 ml of distilled H₂O and 3-4 drops of phenolphthalein indicator. Titrate with the 0.05 M NaOH. The endpoint signal is the first pink coloration that persists for 30 seconds. Repeat the titration using a fresh 50-ml aliquot of the diluted unknown solution, this time using 3-4 drops of methyl red indicator. Repeat the titration until you have used all five indicators. Note, it will be necessary to prepare a second 250-ml batch of the dilut