KoolAid and similar drinks as convenient laboratory reagents: The weak acid-strong base titration of citric acid or malic acid

assorted powdered drink mixes, KoolAid, Gatorade, etc

The major constituent of a KoolAid or a similar non-carbonated soft drink will probably be either citric acid, malic acid, or a mixture of the two acids. Either of these two weak fruit acids provides a pleasant taste and an acidity level that makes the drink palatable. Previously published studies1,2 have shown that it is possible to successfully titrate fruit juices containing weak organic fruit acids against 0.1 M NaOH solution. This is a weak acid-strong base titration.

The details of an experimental trial of ready-todrink KoolAid Jammers3 are presented below. The trial demonstrated that it is feasible to titrate such coloured drinks using the visible indicator phenolphthalein so long as a weakly coloured flavour is chosen. The colour cannot be intense or red. As with many fruit juices and soft drinks, the titratable acidity level of H+ ion is in the range 0.02 to 0.04 mol/L.

Packaged solid drink powders may contain solid citric acid monohydrate (CAM) or a mixture of solid CAM and malic acid (MA), while multi-portion liquid concentrates generally contain malic acid alone. You will know whether the drink contains citric acid or malic acid from the ingredient label of the product used. Using the calculated result for titratable acid concentration, the students can calculate the content level of the fruit acid in the drink, as the molarity of the fruit acid (mol/L), and as g/L of fruit acid. It is conventional to calculate and report the result in terms of the major acid content.

The most convenient form of such drinks for teaching purposes is probably a single-portion packaged solid4. Packages require little shelf space, are indefinitely shelf-stable, and require only to be dissolved in the appropriate amount of distilled water. Canadian readers may not be able to use KoolAid in this form, as KoolAid does not market the powder form in Canada. Never fear, fellow Canadians, other brands or house brands of solid powders such as Gatorade, Tang or Walmart Great Value are available5. A small container of KoolAid liquid drink concentrate is another alternative6.

Using either a solid powder containing CAM or a liquid concentrate containing MA to provide the acid solution for a titration experiment has advantages over the usual alternatives: convenience; low cost; safety; ease of disposal; connections to other course content; a connection to real world chemical analysis; and potential extension to other analyses:

Cost. Pre-packaged powders or containers of liquid concentrate are very inexpensive compared to alternatives such as mineral acids, vinegar or fruit juices.

Convenience. Pre-packaged powders or containers of liquid concentrate are easy to transport. They require little shelf space and no special storage until dissolved/diluted in water. They are very soluble and are easy to fully dissolve.

Safety for the teacher. These reagents are safer and simpler to use than diluting mineral acids or vinegar.

Safety for the students. These drinks are food-safe. There is little hazard to hands or clothing other than staining by the food dyes. The danger to eyes, skin, and clothing is far lower than for using a mineral acid.

Disposal. The small volumes of waste solutions are non-toxic and may be safely put down any sink drain.

 

Titration Curve of pH versus Added Titrant and Indicator Choice

An excellent summary of the distinction between a strong acid-strong base titration curve and a weak acid-strong base titration curve and visual indicator choice for titration was found at the 8. This site gives access to the entire text of “Chemistry”, an open access chemistry textbook created by OpenStax. The entire text may also be accessed via the OpenStax website8.

The pH titration curve of either a citric acid solution or a malic acid solution with sodium hydroxide solution will be very similar to the titration of an acetic acid solution illustrated in the reference. There is a buffer solution region during which the pH rises slowly, followed very near the equivalence point by a rapid rise in pH from around pH 6 to above pH 9. The proper choice of a visual indicator to signal the end-point of the titration is critical. As shown in the reference, phenolphthalein is an excellent choice for such titrations. These titrations meet all of the requirements for a successful analytical titration method: known equation stoichiometry; sufficiently rapid reaction; equilibrium sufficiently close to complete reaction; and end-point indication sufficiently close to the equivalence point.

 

Trial Titrations of KoolAid Jammers

A study was carried out in order to determine whether coloured KoolAid drink solutions can be successfully titrated using 0.1 M NaOH solution with phenolphthalein as indicator. The study method and results are described here. The conclusion is that indeed KoolAid or similar drinks may be used as convenient reagents for the secondary school laboratory. Your students may enjoy the experience of being quality control analysts of a food product.

Five boxes of Kool-Aid Jammers were purchased3, of different lot numbers. There were two boxes each of Strawberry-Kiwi and Tropical Punch and one box of Orange, only one lot number of Orange being available. These are flavours which are not intensely coloured, and which are not predominantly red. This was to facilitate titration of the acid content of each type of KoolAid using phenolphthalein indicator. Two of the ten drink pouches in each box were selected at random for analysis.

The method used was similar to that given in the student instructions below. A narrow-bore 10 mL TC (‘to contain’) graduated cylinder was utilized to maximize precision. One sample only was titrated from each pouch. The beaker, dropper pipet, and graduated cylinder were pre-rinsed with the first sample. The first sample was then poured from its pouch, into the beaker. A 10 mL sample was measured into the graduated cylinder with the aid of the dropper pipet. The sample was washed out of the graduated cylinder in each case with 10 to 15 mL of distilled water into a clean flask. Indicator solution was added to the flask. After titration of each sample, the beaker, dropper pipet, graduated cylinder and titration flask were then rinsed out with distilled water. The procedure was repeated for each sample in turn.

The solutions were titrated gravimetrically9 against a standard 0.1000 M NaOH solution10. A precision Nalgene capillary-dropper polymer squeeze-bottle containing the sodium hydroxide solution was employed11. This bottle releases solution only when squeezed and is easy to control. The end points were all easily discernable and occurred within one drop of the final addition. The density of the sodium hydroxide solution is so close to 1 g/mL that the mass of titrant and the volume of titrant may be considered to have the same value12. Previously published articles9 cover the practicalities of such titrations and the calculations of citric acid titrations.

Table 1: Gravimetric Titration Results and Calculated Values - * CA = Citric Acid (indicates the concentration of citric acid in the drink solution) ** CAM = Citric Acid Monohydrate (indicates the mass of citric acid monohydrate in the powder per litre of drink solution) 

The maximum variation in this small sample set was about 3% between replicate pouches, and about 6% between the two boxes of Tropical Punch. The acid molarity column in Table 1 is the calculated molarity of titratable hydrogen ion in each solution. The molarity of citric acid can be calculated by dividing each value by three. It is interesting to note that each flavour seems to have a different acid concentration, probably part of what makes each drink distinctive from the others in taste.

Conclusion. Assuming that KoolAid Jammer solutions have the same acid concentration values as all other forms of the same flavours of KoolAid, then any form of KoolAid solution could be used as a laboratory reagent for weak acid - strong base titrations. The acid concentration (H+ ion concentration) varies with the flavour. Since other brands of drink solutions are unlikely to be much different from KoolAid, it is probable that any such drink can be used for class experiments.

Note: The experimental values for Tropical Punch Jammers are anomalous. According to the package content masses of the corresponding KoolAid powders (Ref. 4), the citric acid content of tropical punch ought to be in between those of the orange and strawberry-kiwi flavours. See Questions for Students Nos. 8 and 9 for a method of calculation of these values. I am very confident of my titration results. My hypothesis is that the formulation of the Canadian tropical punch Jammers I analysed in 2012 was not the same as the present US formulation. The takeaway from this is that a trial titration has to be carried out before using or reusing any consumer product in an experiment, because the formulation can be changed without notice.

Concepts: 
acid/base
titration
Concepts: 

Course content connections:

  • This experiment would be part of the topic of acid-base chemistry;
  • A titration curve of pH and the choice of a visual indicator may be part of your course content;
  • The titration calculation requires the use of a balanced equation. Since the reactions of citric acid and malic acid with sodium hydroxide are respectively 3 moles and 2 moles to one mole, the calculations when using these reagents requires a review of the use of balanced equations;
  • A calculation of the g/L content of acid in the drink requires the use of the molar mass of the acid;
  • If your course content includes organic chemistry, the structures of citric acid and malic acid may be utilized;
  • Since citric acid is present in the packaged powder as the crystalline monohydrate, the formula of a solid hydrate and its molar mass may be introduced or reviewed.

Extensions. Other analyses of consumer products are possible, such as the amount of citric acid in sour-lemon-flavoured hard candies7, comparisons of titratable acid in fruit juices and other drink types1,2, etc..

Materials: 
  • 0.10 M NaOH solution
  • a number of packages of KoolAid or similar product
  • distilled water
  • phenolphthalein indicator solution

Detailed information regarding KoolAid, Citric Acid and Malic Acid: PDF icon 

Procedure: 

Replacing a strong acid in an existing titration experiment. If you are already using a strong acid for a titration experiment, substitute the drink solution for your previous analyte solution, and use/switch to phenolphthalein as the indicator. As shown by the Trial Titrations section above, a 10 mL sample of drink solution will likely require about 2 to 4 mL of 0.1 M NaOH solution for neutralization, varying with brand and flavour. If this titration volume is smaller than you would wish, you have two options:

  • use a larger volume of the regular drink solution
  • or perhaps more conveniently, use a multiple-strength drink solution as the sample. For example, a triple-strength (3×) KoolAid Orange or Strawberry-Kiwi flavour drink solution will have a titratable concentration of H+ very near 0.1 M, and could replace 0.1 M HCl without any change in your experiment instructions

Using a polymer squeeze-bottle titration method. For a new experiment, consider using the drop-dispensing polymer squeeze-bottle method of titration described below. In my own experiments a good quality capillary-tip polymer drop-dispensing squeeze-bottle is used to dispense 0.1000 M NaOH10 solution to titrate the sample of drink solution. A bottle such as the 6 fl. oz. (60 mL) size Nalgene bottle shown in the photograph is ideal for this purpose11. My titrations employ a gravimetric determination of the amount of 0.1000 M NaOH used. However, if you do not wish to employ a balance or balances for student use, the method for drop-count titrations is identical.

A dropper bottle titration method offers convenience, speed, and good precision. Student instructions for the experiment follow. The titration instructions are identical for either a dropcount or a gravimetric titration. The difference is the analytical measurement of the amount of 0.1 M NaOH solution used: the number of drops of titrant or the mass in grams of titrant respectively.

A study13 showed that for a bottle held vertically, the drop count for a 100 drop sample was 23 drops per mL. The mean drop size was 0.044 g with a standard deviation of 0.001 g and a range of 0.005 g. Measurements were made in g of distilled water, but may be taken as either g or mL values (See Notes: Mass (g) and Volume (mL) Equivalence of Solutions below).

A dropper-bottle method has been used successfully for gravimetric pH titrations in an analytical chemistry course14. I have also used the method with 12 and 13 year old students on open house days at Mohawk College, and on a visit to a school in Toronto13. Almost all of these students were able to use a dropper-bottle proficiently for titration within a few minutes.

You can try out a dropper bottle titration without having to buy Nalgene bottles. Over-the-counter eye-drop squeeze bottle empties can be obtained from users or from a local optometrist or ophthalmologist. These bottles are not large enough and are difficult to fill/refill so they are not convenient for student use in this experiment. But they are actually more precise than the Nalgene bottles. A 15 mL artificial tear solution eye-drop bottle can hold enough 0.1 M NaOH solution to perform at least three titrations.

Experiment Instructions

Note: If you foresee that the Standard Labware Method of dispensing the drink solution and preparing the flasks for titration will be too time-demanding, consider using the Two Dropper-Bottle Method of preparation. It differs only in that the analyte sample is dispensed into the Erlenmeyer flask using a dropper-bottle. The titration method is exactly the same for both.

 

EITHER

Standard Labware Method – Preparing to Titrate

This is the method used for my own titrations. This method allows for more than one different drink sample to be analyzed during a session. In the instructions given here, there is one procedure omitted from my own method – pre-rinsing of the beaker, dropper pipet, and graduated cylinder with the analyte solution (see Notes: Pre-Rinsing of Wet Labware below). If the labware used is wet with distilled water when the analyte solution is first placed into the beaker and other labware, this will result in an inaccuracy of unknown magnitude in the result (see Question No. 1). This step has been deleted in order to simplify the experiment and shorten the time needed. If you want your students to do this procedure the instructions are given in the Notes

Preparing the Titration Flasks

  1. Place about 50 to 60 mL of the supplied drink solution into your beaker.
  2. Pour about 10 mL of the drink solution into the graduated cylinder. Use the dropper pipet to adjust the level in the cylinder to the 10.0 mL mark. Hold the graduated cylinder at eye level to eliminate parallax error.
  3. Pour the drink portion into one of the Erlenmeyer flasks. Do not rinse out the cylinder.
  4. Repeat, adding a second portion into the second Erlenmeyer flask.
  5. To each flask, add approximately 15 mL of distilled water from the wash bottle, and 4 or 5 drops of phenolphthalein acid-base indicator solution. Swirl gently to mix the contents of each flask. The titration station should be well lit. Observe the solution colour in the flask in front of or over a white background.

OR

Two Dropper-Bottle Method (Speed Titration) – Preparing to Titrate

In this method, the analyte solution is added to the titration flask using a dropper bottle. This method is inspired by the traditional low-technology field test kits15 that pre-date the hand-held electronic instruments now available for many of these tests (see Notes: Drop-Count Field Test Kits below).

There are two major reasons for using a multiple-strength drink solution for this version of the experiment:

  • Adding 10 mL of regular-strength drink solution from a dropper bottle requires about 240 drops – this is very tiring and time-consuming;
  • The 60 mL bottles would have to be refilled too often; certainly after each class does the experiment – this is not good planning.

This method assumes that the multiple-strength drink has an acid (H+) molarity of about 0.1 M, equalling the concentration of the NaOH solution. That way, both the drop counts will be about equal, and equally precise. The target would be for about an 80 drop sample of the analyte solution. This is enough of a drop count to provide reasonable precision, without being overly tiresome. The required multiple will have to be determined by trial titration of the drink sample used, and adjusted by experience. 

Rinse and Waste Disposal. All waste is non-toxic and may be discarded to a municipal wastewater system. Either discard directly to a sink or use collection vessels. Clean up spills as instructed as quickly as possible.

Preparing the Titration Flasks

  1. To each titration flask, add about 80 drops of multiple-strength drink solution. Record the number of drops added to each flask. Hold the dropper bottle vertically over the flask mouth. When the bottle becomes hard to squeeze, turn it upright and allow air to enter to equalize the pressure inside to atmospheric.
  2. To each flask, add approximately 25 mL of distilled water from the wash bottle, and 4 or 5 drops of phenolphthalein acid-base indicator solution. Swirl gently to mix the contents of each flask. The titration station should be well lit. Observe the solution colour in the flask in front of or over a white background.

THEN

Titrating

If titrating gravimetrically, the NaOH solution bottle must be kept clean and dry. The drop count is determined and recorded for both drop count and gravimetric titrations. In both cases, this will allow the second and subsequent titrations to be slowed as the end-point volume is neared.

1. If titrating gravimetrically, tare the balance to zero, then place the NaOH bottle on the pan. Read and record the mass to two places after the decimal point (e.g. 75.61 g).

2. For both drop count and gravimetric titration, the drop count to the end-point colour change will be determined and recorded.

3. Trial 1. Add 0.1 M NaOH solution titrant to one of your flasks 5 drops at a time. Hold the bottle in a vertical position above the mouth of the flask.

4. Watch carefully to see if a colour change occurs where the drops enter the solution. Swirl carefully without splashing after each addition. Compare the colour in the flask to that in the as yet unreacted flask. When the bottle becomes hard to squeeze, turn it upright and allow air to enter to equalize the pressure inside to atmospheric.

Absorption of carbon dioxide from the air will cause a slow fading of the redness when close to the end-point. For this reason, the usual instruction is to demand a colour change that remains for more than 30 seconds to indicate that the titration has been completed.

5. Continue until the initial reddishness around the added titrant lasts more than a few seconds. Gradually slow down the rate of titration, observe, and then swirl before another addition. When the colour change observed requires several seconds or longer to fade, slow to adding one drop at a time. Use a stream of distilled water from the wash bottle to rinse all splashed solution down into the solution at the bottom of the flask. The objective is to stop the titration at the point where one more drop will cause a significant colour change to a more reddish hue. This is not easy on the first titration, but will be easier when you know what to look out for. 

6. For a gravimetric titration, repeat the mass determination of Step 1. For both types of titration, record the drop count to the point before one more added drop causes the large colour change. The ideal will be to measure the mass of the bottle or the drop count before adding the drop that causes a major colour change.

7. Trial 2. Repeat steps 3 to 6 for the sample in the second flask. You can safely add the titrant up to about 10 drops ahead of the expected end-point volume all in one go. Then slow down to adding one drop at a time. Try to stop when the next drop will cause the big colour change. Measure and record the end mass of the bottle if required, or the titration drop count if required.

8. Discard the contents of the flasks to waste. Rinse the flasks with two small portions of distilled water.

9. Subsequent Trials. Prepare samples for two more trials.

10. Continue doing trials until you have three satisfactory results in all. For drop count titrations, three satisfactory results will have a range of no more than 5 drops from least to most. For gravimetric titrations, three satisfactory results will have a range of no more than 0.20 g from least to most.

Teaching Note: adjust the target ranges as needed based on experience with your students.

Calculations

Determine the mean value of the three (or more) titrations within the accepted range. Use this value for your calculations.

  • If using the gravimetric method, convert the mass of titrant NaOH solution in g units to a volume in mL units (see Note: Mass (g) and Volume (mL) Equivalence of Dilute Aqueous Solutions).
  • If using the drop-count method, use the mean drop volume value provided by your teacher to convert the mean number of drops into a volume in mL units (see Note: Calibration of Dropper Bottles for Drop-Count Titration Calculations).

Use the calculation method suggested by your teacher. You should be able to use the balanced chemical equation of the analytical reaction to determine: the molarity of H+ ion in the drink solution; the molarity of the fruit acid; and the g/L concentration of the fruit acid.

Notes

Preparation of a Standard Drink Solution. A re-purposed 1 gallon (4 L) distilled water jug is a suitable vessel for the preparation and storage of a drink solution. Clean and then rinse the jug and cap with small portions of tap water then distilled water. Add the required amount of powder or liquid concentrate to make 2 quarts (2 L) of the drink. Add the required amount of distilled water. The amount of water added need not be precisely metered. Even if you could add the water with high precision, replicate batches of solid powder or additions of liquid concentrate are unlikely to be precisely similar. Mark the fill line on the outside of the container for future batch preparation. Cap securely. Mix until all of the solid has dissolved. Ensure uniformity by making 10 slow inversions. Label the jug.

Preparation of a Multiple-Strength Drink Solution. A re-purposed 1 or 1.5 quart (1 or 1.5 L) wide-mouth juice bottle with a screw cap is a suitable vessel for the preparation and storage of a drink solution. Clean and then rinse the bottle and cap with small portions of tap water then distilled water. Add the required amount of powder or liquid concentrate to make 2 quarts (2 L) of the drink. But in this case, add only the amount of distilled water required to make to make a your required multiple-strength drink solution. For example, about 500 mL to make a quadruple-strength solution. The amount of water added need not be precisely metered. Even if you could add the water with high precision, replicate batches of solid powder or additions of liquid concentrate are unlikely to be precisely similar. Mark the fill line on the outside of the container for future batch preparation. Cap securely. Mix until all of the solid has dissolved. Ensure uniformity by making 10 slow inversions. Label the bottle.

Preparation of 0.1 M NaOH solution. Preparation of a standardized solution of 0.1 M sodium hydroxide from solid pellets of NaOH that is uncontaminated by sodium carbonate is both a hazardous and a complex procedure. Solid sodium hydroxide is the exemplar of a hazardous solid16. The solid adsorbs both water and carbon dioxide from the air. It is safer to purchase and dilute a concentrated NaOH solution of known molarity, for example 3.0 M17. A 1 L bottle of a 3 M solution would provide up to 30 L of 0.1 M NaOH solution for this exercise.

Why does Fisher Scientific label and purvey this solution as 3 N (normality) rather than 3 M (molarity)? It is because vendors cater to the industrial users who will purchase this solution (e.g. water treatment, sewage treatment, swimming pool, environmental, metal cleaning, electroplating, etc.) and who are following instructions written many years ago in the language of normality, not molarity. These users cannot translate between normality and molarity as chemists can, and must have a product label that matches the protocol they follow. For example, see: https://www.tpomag.com/editorial/2014/05/understanding_alkalinity

Standardization of 0.1 M NaOH Solution. There is no compelling reason to standardize the sodium hydroxide solution used by the students. You can tell the students it is 0.1 M. However, it would be wise to prepare a solution that is close enough to 0.1 M that the students’ results are credible. The amount of solution prepared should be sufficient for the experimental work for at least one class so that all of the results are comparable. Once prepared, the drink solution to be used should be trial titrated beforehand using the sodium hydroxide solution that has been prepared for use, to ensure that the resulting values are acceptable.

If you are a perfectionist, purchase a bottle of certified 0.1000 M NaOH for your own use10. Use this standardized 0.1000 M solution to titrate and standardize your prepared drink solution. Very little volume will be required. Then titrate the now standardized drink solution against the sodium hydroxide solution prepared for student use in the experiment, thus determining its NaOH concentration.

Polymer Capillary-Tip Drop-Dispensing Squeeze-Bottles. Capillary-tip controlled drop-dispensing polymer squeeze-bottles can be used for either gravimetric titration9 or drop-count titration13. The titration method is identical. Unless you have sufficient two-place balances available, drop-count titration is recommended. My preferred bottle type is the Nalgene11. The polymer wall of this bottle is thick and stiff, so the bottles are very durable and ideal for titrations. The bottles are hard to squeeze, but nothing comes out even when the bottle is fully inverted. We have used these bottles at Mohawk College for many years for all manner of purposes and solutions. They are indestructible. Examples of use are: indicator dispensing; microscale experiments with indicators, buffers, redox reagents, precipitations, complexation, corrosion, etc.; dispensing small volumes of acids and bases in numerous experiments.

For drop-count titrations, compared to using eye-droppers or capillary tip pipets, using squeeze-bottles reduces both the likelihood of reagent spills and the chance of dripping reagent, since the bottles are capped and no reagent can be lost when a bottle is upright.

Calibration of Dropper Bottles for Drop-Count Titration Calculations. There are two required properties of the bottles to be used. Firstly, the dispensing of drops must be easily controlled, even when the bottle is inverted. Secondly, the drop size must be consistent, not variable. Using the drop count of base required to neutralize samples of acid for calculation can only make sense if the drop size from the dropper bottles is consistent and reproducible.

The Table 2 gives the result of weighing successive drops of distilled water from each of three types of sample bottle on a 4-place analytical balance. The balance door was open, and the last place (0.1 mg) was unsteady, so each reading was rounded to the third place (to the nearest 1 mg).

The percent relative standard deviation (% RSD) of both types of 60 mL dropper bottles was about ± 2.5 %. Notice that the ‘medical grade’ Tears II bottle, an overthe-counter synthetic-tear eye-drop, had a much more consistent drop volume. This type of delivery system for medication is subject to FDA/USP regulation 90518,19, which mandates that the amount of medication delivered in successive doses be within an RSD of ± 2.5 %, and that includes variability of the solution in different bottles as well as both inter-bottle and intra bottle variability.

You can have your students use my values from the table for mean drop volume for a bottle. But if time permits the students can easily calibrate the bottle(s) they used for the experiment. A calibration method is given in Question 5: measuring the volume of a 100 drop sample. An alternative is to count drops to a precise volume, e.g. 5.0 mL.

Pre-Rinsing of Wet Labware.

  1. The beaker, the graduated cylinder, the dropper pipet, and the Erlenmeyer flasks should be cleaned, then rinsed with two small (10 mL) portions of tap water, then rinsed with two small (10 mL) portions of distilled water. Leave wet. Do not lay the dropper pipet on an unclean surface.
  2. Rinse 1. Place about 10 mL of regular-strength analyte drink solution in the beaker. Swirl, tip and rotate the beaker to wet the walls with this solution. Use the rinse portion to fully wet the inside of the dropper pipet. Return the rinse to the beaker. Pour the rinse portion into the graduated cylinder to fully wet the inside walls. Discard the rinse portion as instructed.
  3. Rinse 2. Repeat the rinse and discard as before.

Drop-Count Field Test Kits. Field test kits are made by a number of laboratory supply companies15. These test are portable, and are based on simple wet chemistry. They are either based on a drop-count titration using an eye-dropper, or are based on a colour development reaction with a colour comparison chart. The drop-count titrations are usually in the range of 15 – 25 drops, so while the chemistry of a test may be highly accurate, the precision is low, ± 5 % or even ± 10 % being typical. Field tests are designed to be low precision, but easy to perform rapidly, so that many tests may be performed in a short time. They are mainly used to survey or detect problems, in which case documented samples are gathered and returned to a testing laboratory for further analysis.

Mass (g) and Volume (mL) Equivalence of Dilute Aqueous Solutions. The densities of most dilute aqueous solutions are very near 1 g/mL. For gravimetric titrations with dilute aqueous solutions, it causes only a very small error to take the volume of solution used as an amount in mL units equal to the mass in g units of the solution used12.

Example Data: density of 0.125 M NaOH at 20 ºC = 1.0039 g/mL density of 0.052 M CA at 20 ºC = 1.0022 g/mL

The error introduced by equating mass (g) to volume (mL) for 0.1 M NaOH and 0.03 M citric acid is therefore below 1% and is not significant for this experiment.

 

Questions: 

Download a worksheet including the following questions: PDF icon 

1. Students began a titration experiment with labware (beaker, graduated cylinder and dropper pipet) that was wet with small amounts of distilled water. This caused a small error in their results. Explain why this caused an error, and whether their result for the acid content of the drink solution was higher or lower than the actual true value.

2. The Erlenmeyer flasks used for student titrations were wet with distilled water after rinsing. This did not cause any error in the experiment results. Explain why the presence of distilled water in the flasks did not affect the results.

3. A 10.0 mL sample of a regular strength drink solution containing citric acid required 3.65 mL of 0.1000 M NaOH solution for the titration. Calculate (a) the molarity of H+ in the drink solution (b) the molarity of citric acid (c) the g/L content of citric acid, and (d) the g/L content as citric acid monohydrate. Show all of your calculation steps.

4. A 10.0 mL sample of a regular strength drink solution containing malic acid required 86 drops of 0.1000 M NaOH solution for the titration. The mean drop volume for the dropper bottle was 0.0440 mL. (a) Calculate the volume of NaOH solution required (b) the molarity of H+ in the drink solution (c) the molarity of malic acid (d) the g/L content of malic acid, Show all of your calculation steps.

5. A calibration of a dropper bottle found that 100 drops of distilled water from the bottle into a graduated cylinder had a volume measured as 4.50 mL. Calculate the mean drop volume delivered.

In olden times, before instrumental methods became ubiquitous, manual titration was the main method of chemical analysis. This was before PCs and hand calculators! To save time in calculating results, a titration solution would be labelled with its titre value for a particular analysis:

6. Verify by the use of the balanced chemical equation that the titre of 0.1 M NaOH solution for citric acid is 1 mL (or 1 g) = 6.40 mg citric acid. Show all calculations in full, including unit conversions.

7. Verify by the use of the balanced chemical equation that the titre of 0.1 M NaOH solution for malic acid is 1 mL (or 1 g) = 6.71 mg malic acid. Show all calculations in full, including unit conversions.

8. A regular-strength Orange KoolAid drink solution made from a package of powder4 was titrated using 0.1000 M NaOH solution. The package content lists citric acid as the acid present in the drink. The titration of a 10.0 mL sample required 3.10 mL of the NaOH solution for neutralization:

a. The package contained 0.15 oz mass (US) of powder (1 oz mass = 28.35 g). Convert the mass of the powder to g units.

b. The package was intended to prepare 64 oz liquid (US) of drink (1 oz liquid = 29.6 mL). Covert the volume of the mixed drink solution to mL units and to L units.

c. Use the titre value, 1 mL 0.1 M NaOH = 6.40 mg citric acid, to calculate the mass in g units of citric acid present in the 10.0 mL sample.

d. Calculate the mass of citric acid present in the entire package, in g units.

e. The package of solid actually contains citric acid monohydrate (210.1 g/mol), not citric acid (192.1 g/mol). Calculate the mass of citric acid monohydrate present in the entire package, in g units.

f. Calculate the percentage by mass of citric acid monohydrate in the solid in a package of Orange KoolAid powder, to the nearest 1%. g. Does your answer make sense? Explain your answer.

9. A package of Strawberry-Kiwi KoolAid powder4 was dissolved in 64 liquid oz. US of distilled water. The package lists “citric acid” among its ingredients, total weight of the powder being 0.17 oz. weight US. Assume that the actual ingredient is citric acid monohydrate comprising 92% of the powder. Predict the titration volume of 0.1000 M NaOH solution required to neutralize a 10.0 mL sample of this KoolAid solution. Show all of your calculation steps.

Preparation: 

Collect one or more types of drink mixes or citric acid for students to test. 

Attribution: 
  1. Cash, David, “”, Chem 13 News, University of Waterloo, Dec 2012/Jan 2013.
  2. Cash, David, , Chem 13 News, University of Waterloo, Oct 2013.
  3. KoolAid Jammers Premixed Drinks, KoolAid.com: (strawberry-kiwi) https://www.koolaid.com/en/product/00043000028278 (tropical punch) https://www.koolaid.com/en/product/00043000028254 (orange) https://www.koolaid.com/en/product/00043000028216
  4. KoolAid Drink Powder Packages, KoolAid.com: (strawberry-kiwi) https://www.koolaid.com/en/product/00043000955277 (tropical punch) https://www.koolaid.com/en/product/00043000955437 (orange) https://www.koolaid.com/en/product/00043000955314
  5. Tang Orange Flavor Crystals, Walmart Canada: https://www.walmart.ca/search?q=Orange%20Flavor%20Crystals
  6. KoolAid Orange Liquid Drink Mix, kraftcanada.ca: https://www.kraftcanada.ca/product/kool-aid-orange-liquid-drinkmix-00068...
  7. Cash, David, , Chem 13 News, University of Waterloo, April 2014.
  8. OpenStax Chemistry Textbook, Chapter 14, Section 7: https://opentextbc.ca/chemistry/chapter/14-7-acid-base-titrations/ or http://cnx.org/contents/85abf193-2bd2-4908-8563-90b8a7ac8df6@9.311
  9. Prof. D. Cash Web Page Downloads, Gravimetric Titrations: a. https://www.uclmail.net/users/dn.cash/GravTitr1.pdf (includes detailed calculation methods) b. https://www.uclmail.net/users/dn.cash/GravTitr2.pdf (includes pH titration curves) c. https://www.uclmail.net/users/dn.cash/GravTitr3.pdf (includes details about polymer squeeze bottles)
  10. Fisher Scientific, certified 0.1000 M NaOH solution: https://www.fishersci.ca/shop/products/sodium-hydroxidecertified-0-1000n...
  11. ThermoFisher, 60 mL Nalgene Dropper Bottle, 12 Pack or 48 Pack: https://www.thermofisher.com/order/catalog/product/2411-0060PK https://www.thermofisher.com/order/catalog/product/2411-0060
  12. Handbook of Chemistry and Physics, CRC Press, 54th Edition, 1973-1974, Concentrative Properties of Aqueous Solutions, Citric Acid (CA), page D-198 and Sodium Hydroxide, page D-225. (density of 0.125 M NaOH at 20 ºC = 1.0039 g/mL; density of 0.052 M CA at 20 ºC = 1.0022 g/mL)
  13. Prof. D. Cash Web Page Download, “Comparing the Acid Content of Fruit Juices and Other Samples by Drop Count Titrations”: https://www.uclmail.net/users/dn.cash/DropCountTitr.pdf
  14. Mohawk College Experiment Download, “pH Meter and Gravimetric Titrations”: https://www.uclmail.net/users/dn.cash/pHMeter.pdf
  15. Hach Company: https://www.hach.com/populartestkits https://www.hach.com/family-print.pdf.jsa?productCategoryId=35547009716 https://ca.hach.com/family-print.pdf.jsa?productCategoryId=22746996607 https://ca.hach.com/single-parameter-test-kits/drop-count-titration-test...
  16. American Chemical Society, Guidelines for Chemical Laboratory Safety in Secondary Schools, Page 30:
  17. Fisher Scientific, certified 3 M NaOH solution: (https://www.fishersci.ca/shop/products/sodium-hydroxide-3-0nstandardized...)
  18. United States Pharmacopia (FDA) Regulation 905: https://www.usp.org/sites/default/files/usp/document/harmonization/gen-m...
  19. Cash, David, , Chem 13 News, University of Waterloo, Dec 2016/Jan 2017.
  20. Peynaud, Émile, The Taste of Wine: The Art and Science of Wine Appreciation. trans. Michael Schuster. London, Macdonald Orbis, 1996, ISBN 0-471-11376-X, pages 176-177 and 208.
  21. Cash, David, “Carboxylic Acids in Wine”, Chem 13 News, University of Waterloo, Oct 2006, pages 12 and 13.
  22. Cash, David, , Chem 13 News, University of Waterloo, Nov 2014 and , Chem 13 News, University of Waterloo, Dec 2015/Jan 2016.
  23. Inexpensive Purchase of Citric Acid Monohydrate and Malic Acid: https://www.fishersci.com/shop/products/citric-acid-monohydrate-24/S2525... https://www.fishersci.com/shop/products/dl-malic-acid-98-thermo-scientif... https://modernistpantry.com/products/citric-acid.html?_ga=2.30018367.106... 1573004696.1650133903 https://modernistpantry.com/products/malic-acid.html https://www.fibregarden.ca/product/citric-acid/

 

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Safety

General Safety

For Laboratory Work: Please refer to the ACS .  

For Demonstrations: Please refer to the ACS Division of Chemical Education .

Other Safety resources

: Recognize hazards; Assess the risks of hazards; Minimize the risks of hazards; Prepare for emergencies