pH Determination

DEPARTMENT OF FOOD SCIENCE AND TECHNOLOGY College of Agriculture and Food Sciences Visayas State University Visca, Baybay City, Leyte Name: Jadess Lorraine Z. Fusio Tuesday 1:00-4:00 PM

Date Performed: November 17,2015 Date Submitted: December 1,2015 Ftec 122 – Food Analysis LaboratoryExercise No. IA pH Determination

Introduction pH is a measure of the acidity or alkalinity of a water solution. The acidity or alkalinity of a water solution is determined by the relative number of hydrogen ions (H+) or hydroxyl ions (OH-) present. Acidic solutions have a higher relative number of hydrogen ions, while alkaline (also called basic) solutions have a higher relative number of hydroxyl ions. Acids are substances which either dissociate (split apart) to release hydrogen ions or react with water to form hydrogen ions. Bases are substances that dissociate to release hydroxyl ions or react with water to form hydroxyl ions. If the hydrogen ion concentration is very high, the pH value is very low. This is determined using a scale ranging from 0-14 called the pH scale. It was introduced by a Danish chemist Soren Peder Lauritz Sorensen. Substances with pH lower than 7 are acidic, those with pH equal to 7 are neutral and those with pH greater than 7 are basic in nature. Objectives • • •

To determine the pH of different solutions using pH meter. To have knowledge on the different ways on how to properly use a pH meter. To identify which among the solustions is the most acidic and basic.

Methodology pH meter was used to determine the pH values of the different solutions. In order to properly have a precise value, different measurement procedure was followerd in this laboratory experiment. First, when the push button “off” is depressed it indicates that the pH meter is switched on. The electrodes was then connected to immersed in a buffer solution. Then, the temperature control was set to buffer temperature and the pH button was immediately pressed. The pH value of the buffer solution on the scale was also set together with the asymetry control. For now the instrument is calibrated and ready to use. Then, the electrode was removed from the buffer soltion and the membrane and salt bridge was washed down with distilled. In line with this, it was also noted that the membranes with the spout of the water bottle must never be touched. The electrodes was then wiped with tissues. Lastly, the electrode was lowered into the test solutions and the pH read button was press to obtain the said pH value of the different solution.

Results and Discussion

Solutions •

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pH Values

Vinegar Silver Swan

2.79

Datu Puti

2.72

Coconut Vinegar

3.13

Soft Drinks Coke

2.58

Sprite

3.32

Royal

2.99

Beverage Cofee

6.24

Milk

6.45

C2

3.81

Juices Zest-O

3.26

Plus (Orange)

3.14

Calamansi Juice

2.6

Table 1.0 pH values of different liquid solutions. pH is a measure of the acidity or alkalinity of a water solution. The acidity or alkalinity of a water solution is determined by the relative number of hydrogen ions (H+) or hydroxyl ions (OH-) present. Acidic solutions have a higher relative number of hydrogen ions, while alkaline (also called basic) solutions have a higher relative number of hydroxyl ions. Acids are substances which either dissociate (split apart) to release hydrogen ions or react with water to form hydrogen ions. Bases are substances that dissociate to release hydroxyl ions or react with water to form hydroxyl ions. pH is measured using a pH meter of a glass electrode. A pH meter generally comprises a detecting unit consisting of a glass lectrode and a reference electrode, and an indicating unit for indicating the pH value coresponding to the electromotive force detected fundamentally represents the value of hydrogen ion activity in solutions. The pH electrode uses a specially formulated, pH sensitive glass in contact with the solution, which develops a potential (voltage) proportional to the pH of the solution. The reference electrode is designed to maintain a constant potential at any given temperature, and serves to complete the pH measuring circuit within the solution. It provides a known reference potential for the pH electrode. The difference in the potentials of the pH and reference electrodes provides a millivolt signal proportional to pH.

In this laboratory experiment, the different pH of liquid solutions namely vinegar, soft drinks, beverage and juices was determined to identify which among those solutions are acidic or basic using a pH meter. Identifiying the different solutions of food product will help one identify the level of pH intended for the specific product. Based on the gathered results, the most acidic solution was coke which had the lowest pH value of 2.58 while the most basic solution was milk which had the highest pH value of 6.45. The results implies that acidic solutions are substances that produce free hydrogen ions (H+ions) when dissolved in water. Bases are substances that produce hydroxyl ions (OH - ions) when dissolved in water. Acidic solutions are rich in hydrogen ions and basic solutions are poor in hydrogen ions. Some acids dissociate only partly, releasing very small amounts of H +ions, and are called weak acids. Others dissociate completely, releasing large amounts of H +ions, and are called strong acids. In the same way, bases that dissociate partly are called weak bases and those that dissociate completely are called strong bases. Conclusion Therefore, liquid solutions olutions with a pH less than 7 are acidic and solutions with a pH greater than 7 are alkaline or basic.Contrary to popular belief, the pH value can be less than 0 or greater than 14 for very strong acids and bases respectively. If the hydrogen ion concentration is very high, the pH value is very low. It is also important to know the pH or the concentration of the acid in a food product for understanding the product's properties and for the quality control of commercial products. Questions and Answers 1. Review the relationship between pH and hydrogen-ion concentration of solutions. Discuss briefly. Answer: The relationship between pH and hydrogen-ion concentration is direct. PH and H+ are both on the nomerator. As the H+ ion concentration increases, the pH decreases. As the OH- ion concentration increases, the pH increases, the more hydrogen an ion has, the more acidic it is. 2. What is the purpose of calibrating the pH measurement? Answer: The purpose of calibrating the pH measurement is to have a accurate reading and it is required to match the pH meter to the electrodes. For very precise measurement, the pH meter should be calibrated before each measurement. The calibration should be performed with at least two buffer solutions with known pH. For general purposes, buffer solutions with pH 4 and pH 10 are used. For more precise measurements, three buffer solution calibrations are preferred. Acids and bases around the balance point of 4 can be assumed to be the opposite of their actual chemistry if the meter is off and calibrating the pH scale makes the observer understand easily the nature of the substance,i.e. acidic or basic. 3. What are buffer solutions? What is their application to pH determination? Answer: Buffer solutions are one which resists changes in pH when small quantities of an acid or an alkali are added to it. Buffer solutions are necessary or needed to keep the correct pH for enzymes in many organisms to work.

4. What is the importance of knowing the pH of food materials in food processing? Answer: The importance of knowing the pH of food materials in food processing is that certain foods are required to be preserved based on their pH levels. For examples, food with the pH of 5.6 or less must be preserved because of their acidity. It is also important to know the pH to understand the properties of different food product. References • • •

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amrita.olabs.co.in,. (2013). Determination of pH. Retrieved 22 November 2015, from amrita.olabs.co.in/?sub=73&brch=7&sim=144&cnt=1 Bates, Roger G.Determination of pH: theory and practice. Wiley, 1973. Mendham, J.; Denney, R. C.; Barnes, J. D.; Thomas, M. J. K. (2000),Vogel's Quantitative Chemical Analysis (6th ed.), New York: Prentice Hall, SBN 0-582-22628-7, Section 13.23, "Determination of pH" Maloney, Chris."pH calculation of a very small concentration of a strong acid.". Retrieved 13 March 2011.