Buffers in Household Products: Part A
Buffers in Household products
Jihyun Yoo
Introduction
One of the most important applications of acids and bases in chemistry and biology is that of buffers. A buffer solution resists rapid changes in pH when acids and bases are added to it. Every living cell contains natural buffer systems to maintain the constant PH needed for proper cell function. Many consumer products are also buffered to safeguard their activity.
"HOW DO WE DISCOVER WHICH PRODUCTS HAVE BUFFERING CAPACITY?"
Concepts
- Buffer
- Weak acids and weak bases
- Conjugate acid-base pair
- Neutralization
- Weak acids and weak bases
- Dissociation constant
- Titration
Background
Many chemical reactions in living organisms take place in neutral pH values. Even a small change in pH can cause some of nature's catalysts to stop functioning. The pH level in blood, for example, must be maintained within extremely narrow limits.
The ability of buffers to resist changes in pH upon the addition of acid or base can be traced to their chemical composition. All buffers contain a mixture of either a weak acid (HA) and its conjugate base (A-) or a weak base and its conjugate acid. The buffer components HA and A- are related to each other by means of the following chemical reaction that describes the behavior of a weak acid in water.
Buffers control PH because the two buffer components are able to react with and therefore neutralize the strong acid or strong base that might be added to the solution. The weak acid component HA reacts with any strong base, such as sodium hydroxide (NaOH) to give water and the conjugate base component A- (Equation2) reacts with any strong acid, such as hydrochloric acid (HCI) to give its acid partner HA and a chloride ion (Equation 3).
These neutralization reactions can be visualized as a cyclic process. Buffer activity will continue as long as both components are present in solution. Once either component is consumed, the buffer capacity will be exhausted and the buffer will no longer be effective.
A buffer composed of an equak number of moles a weak acid and its conjugate base is generally equally effective in resisting pH changes upon addition of either acid or base. The pH range in which a buffer system will be effective is called is buffer range. The buffer range is usually limited to 2 pH units centered around the pH of the ideal buffer solution. An ideal carbonic acid bicarbonate buffer, for example, has a pH of 6.4 and its buffer range is pH 5.4-7.4
Buffers are also important in certain commercial household products. Sops and shampoos are by nature, alkaline. The addition of citric acid buffers this alkalinity and prevents possible burns to the skin and scalp. Baby locations can contain buffers of citric acid and sodium lactate to buffer the lotion to a slightly acidic pH of six, which inhibits the growth of bacteria and other pathogens. Even alcohol production can rely on buffers. Yeasts that ferment the sugars only work well within a certain pH range. Of the pH is outside the range of 4.0 to 6.0, the yeast growth may be inhibited or even destroyed.
The purpose of this advanced inquiry lab is to investigate the buffering capacity and buffer components of various consumer products. Many household products contain buffering chemicals such as critic acid, sodium carbonate, sodium carbonate, sodium benzoate and phosphates or phosphoric acid.
The lab begins with an generating the titration curve for citric acid to identify the buffering regions in the neutralization of a polypro tic weak acid. The results provide a model for guided inquiry design of procedure to determine the buffering agents in eight different household products, including foods and beverages and over the counter drugs.
Procedure may include creating titration curves, calculating pKa values, and analyzing the buffer capacity and composition. Students may recommend additional consumer products for further inquiry.
Pre-Lab Concept Practices
25.0mL of a 0.10M solution of the weak acid acetic acid, CH3COOH, is titrated with a 0.10M solution of the strong base sodium hydrozide, NaOH Ka of acetic acid is 1.8 x 10^-5. The titration curve is shown in below graph.
1. At what point in the titration does the concentration of acetic acid equal the concentration of the acetate ion?
2. If this weak acid is effective as a buffer between the concentration ratios for the conjugate acid base pair of 10:1 and 1:10, what pH range does this cover?
3. What measurements are needed in the titration of a weak acid? Explain in detail the technique or procedure for adding the titrant to ensure that the concentration and pKa of the weak acid can be accurately determined.
The measurement needs in the titration of a weak acid are the volume of the titrant and the PH of every mL of the titrant added. The pKa of the weak acid, the PH recorded after every mL of the titrant has been added. It will be change in PH that has been reached.
Materials
- C6H8O7 0.02 M 10mL
- HCI 0.1M 150mL
- NaOH 0.1M 150mL
- Water distilled or deionized
- Beakers 150 mL
- Beakers 250 mL
-Buret, 50mL
- Clamp, buret
- Magnetic stirrer and stir bar
- pH sensor or pH meter
- Support stand
- Wash bottle
Introductory Activity: Titration of Citric Acid
It is a common buffer added to consumer products. This weak acid contains three ionizable hydrogen atoms.
1. Set up a pH meter and electrode. Calibrate the pH meter
2. Fill the buret with the 0.1 M sodium hydroxide, NaOH solution
3. Titrate 10mL of a solution of 0.02 M critic acid, C6H8O7 with the sodium hydroxide solution titrant
4. Graph the data with pH on the vertical axis and volume NaOH on the horizontal axis. Make the graph large enough to reflect the care taken with the pH and volume measurements
The table for the titration for Certic Acid
Graph for HC6H8O7
The titration of critic acid analyze the results:
The buffering region of the Cirtic acid titration current ranges from 2.5 to 6.0.
Individual pKa values can not be distinguished in the titration curve of the triprotic acid.
Procedure for titration using gatorade:
1. Powder and mix gatorade with water
2. Acidic, NaOH
3. The solution should be diluted enough to be titrated with reasonable amount of NaOH
- Rough titration to assess
4. By doing a rough titration, you should collect pH at different volumes of NaOH added graph (mL NaOH <x> added, pH <y> )
In details...
1. For this titration experiment, we measure out 0.5g of gatorade powder using a digital scale. We then added it to a beaker that had 5mL of distilled water that was measured using a graduated cylinder. We then added 1 drop of phenolphthalein indicator to the solution, and slowly titrated by increments of 0.5 mL NaOH till we were able to obswerve a color change. From this we learned that we should dillute our solution more because it took a lot of NaOH to titrate this solution and get a color change
2. Calibrate a pH meter using buffers 7.00 and 10.00
3. Measure 0.3g of gatorade powder using a digital scale and then add it to a Erlenmeyer flask with 10mL of distilled water stir to combine this will give you a light red colored solution, thusly making it easier to see the pink color change that will indicate the stoichiometric point
4. add 2 drops of phenolphthalein to your gatorade
5. record the pH of your solution with no titrant added
6. Set up a burette with titrant, NaOH
7. add titrant to gatorade by small increments of 0.5 mL record pH at each increment
8. make a table and graph using the pHs that you have recorded throughout your experiment
Final Data Table and Graph
Graph and table for gatorade powder
Analyze the results
The product contains a buffer.
Half eq = pka = 5.65 -1 +1
Buffering pH range = 4.65 ~ 6.65
Estimate the pKa: The pKa of the buffer should be near the desired midpoint of PH of the solution. Our range of the pH is 4.65 ~ 6.65; therefore our group estimate the pka value for Cirtic Acid at 25 degree of celcius is 4.76
The potential buffering components are cirtic acid and mono potassium
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