Theory And Procedure For Determination Of pH Of Different Solutions Using Indicators And pH Scale
Before understanding, what pH determination is? It is essential to understand what is the meaning of pH. The full form of pH is the potential of hydrogen. It is a quantitative scale that is used to determine or measure the acidity or the basicity of any liquid solution.
For instance, in the case of pure water, the concentration of hydrogen ion is 10 - 7 gram-equivalents per litre, which is considered to be neutral as it falls in the pH 7 category. We say a liquid concentration is acidic if the pH level is less than seven and we say, the liquid concentration is basic or alkaline if the pH is more than 7. This is how the pH of a given solution is determined.
How to Determine the pH Through an Experiment?
There are several experiments through which the pH of a certain liquid concentration is determined; one such is given below.
The theory rests on the fact that each chemical has an inclination towards being a base, or an acid or being neutral. When an acidic liquid is dissolved in the water, it releases free hydrogen ions (H+ ions), whereas, when a base is dissolved in the water it produces hydroxyl ions (OH- ions). The strength or weakness of the acidic solution or basic solution depends on the release of H+ ions or OH- ions when it is dissociated.
Measurement of pH
pH was invented by a Danish chemist named Soren Peder Lauritz Sorensen. The value of the pH will be low if the concentration of the hydrogen atoms is high. pH is defined as the negative logarithm (base 10) of hydrogen ion concentration.
Liquid concentration, whose level is lower than seven on the pH scale, is said to be acidic.
Liquid concentration, whose level is higher than seven on the pH scale, is said to be basic.
Liquid concentration, whose level is equal to 7 on the pH scale is neutral.
pH Determination Methods
There are several methods of pH determination.
pH Paper:
Special strips of paper are made by submerging them in the chemical compound and then drying it. When this paper is dipped on a liquid substance, it changes colour. The change of colour is then compared to the colour chart to determine the actual pH level or in which category that certain liquid belongs.
pH Meter:
there is a device known as the pH meter, which is used to determine the pH level of a substance. This electronic device has a special electronic bulb that is sensitive to hydrogen ions. The ones that are present in the solution. The bulb produces a signal which is then amplified by and is shown in a meter format in the electronic meter attached. The meter displays the pH level and in which category does the substance belong. For very precise measurement, the pH meter should be calibrated before each measurement.
The pH of Fruit Juices
People who are obsessed with the idea of dieting are quite taken by the pH levels of different fruit juices. A study has shown that juices which are lower than pH level 4 or belong to the category of pH 4 can be extremely damaging to the teeth as well as the person's health. For this purpose, the pH of fruit juices is mentioned below:
Lemon Juice - 2.25
Very Fine Grapefruit Juice - 3.22
Minute Maid Cranberry Grape - 2.71
Ocean Spray Strawberry Kiwi Juice Cocktail - 2.90
Ocean Spray Cranberry - 2. 56
Minute Maid Natural Energy Pomegranate Berry - 3.33
Ocean Spray Cran-Grape - 2.79
Minute Maid Orange Juice - 3.82
Minute Maid Cranberry-Apple Raspberry - 2.79
Study of pH of Some Fruit Juices Project Determination of pH of Acid Solutions
There is an easy way to determine the pH level or the acidic level of a given solution.
Aim
Using pH paper and a universal indicator, determine the pH of solutions such as fruit juices containing various acids, bases, and salts.
Apparatus
Test tubes
Universal indicator
pH paper
White tile
Dropper
Some juices
Procedure
Pour the liquid into separate test tubes. Take the white tile and place the strip of paper on it. Take the help of the dropper to extract the liquid which you want to test and put it on the strip of pH paper. As soon as the liquid solution gets in touch with the pH paper, it will start changing colour. Now, match the colour to the universal chart that has been given to you to know if the solution is alkaline or neutral or acidic.
In the case of Cranberry juice, it will be acidic. Cranberry juice falls directly under the category of acidity because its measurement on the pH scale is typically between 2.3 to 2.5. Foods or juices which are above pH level 7 are considered to be basic or alkaline.
Similarly, limes, lemons, and tangerines - all of which are rich in ascorbic acid - feature a pH of 2.4, 3.1, and 4.1, respectively.
Precautions to be Taken During the Experiment
Make a careful match between the colour of the solution and the standard colour pH chart.
Keep the pH strips out of the reach of any chemical fumes.
Maintain the pH paper clean.
Conclusion
pH determination helps people to understand if the given solution is acidic, basic or neutral, which, in turn, helps them to determine which liquids are safe or easy to consume. The way of measuring the pH scale is extremely easy, either that person can use pH paper or pH meter.
FAQs on Determination Of pH Of Some Solution Chemistry Practical
1. What is the aim of the determination of pH of some solution experiment?
The aim of the determination of pH of some solution experiment is to measure the pH value of given solutions and identify whether they are acidic, basic, or neutral.
- pH indicates the concentration of H+(aq) ions in a solution.
- If pH < 7, the solution is acidic.
- If pH = 7, the solution is neutral.
- If pH > 7, the solution is basic (alkaline).
2. What is pH in chemistry?
In chemistry, pH is the negative logarithm of the hydrogen ion concentration, defined as pH = −log[H+].
- [H+] is the molar concentration of hydrogen ions in mol L-1.
- The pH scale usually ranges from 0 to 14 at 25°C.
- Lower pH means higher acidity, while higher pH means higher basicity.
3. How do you determine the pH of a solution in the laboratory?
The pH of a solution in the laboratory is determined using a pH meter or suitable indicators.
- Using a pH meter: Calibrate with standard buffer solutions, immerse the electrode in the test solution, and read the pH directly.
- Using pH paper/universal indicator: Dip the strip into the solution and compare the color with a standard chart.
4. What is the formula used to calculate pH of a solution?
The formula used to calculate pH is pH = −log[H+], where [H+] is the hydrogen ion concentration in mol L-1.
- For example, if [H+] = 1 × 10-3 mol L-1, then pH = 3.
- For strong acids like HCl(aq), [H+] equals the acid concentration.
5. What is the difference between a strong acid and a weak acid in terms of pH?
The main difference is that a strong acid completely ionizes in water, while a weak acid partially ionizes, resulting in different pH values at the same concentration.
- Example of strong acid: HCl(aq) → H+(aq) + Cl-(aq)
- Example of weak acid: CH3COOH(aq) ⇌ H+(aq) + CH3COO-(aq)
- Strong acids generally have lower pH than weak acids of equal molarity.
6. How does a pH meter work in measuring pH?
A pH meter works by measuring the electrical potential difference related to the hydrogen ion concentration in a solution.
- It contains a glass electrode sensitive to H+ ions.
- The electrode generates a voltage proportional to pH.
- The meter converts this voltage into a pH reading.
7. Why is it important to calibrate a pH meter before use?
Calibration of a pH meter is important to ensure accurate and reliable pH measurements.
- Electrode response can drift over time.
- Standard buffer solutions of known pH (such as 4, 7, and 9 or 10) are used for calibration.
- Calibration adjusts the meter to match known reference values.
8. What are buffer solutions and how do they affect pH?
A buffer solution is a solution that resists changes in pH when small amounts of acid or base are added.
- It usually contains a weak acid and its salt, such as CH3COOH/CH3COO-.
- Buffers maintain nearly constant pH.
- They are used to calibrate pH meters and maintain stable pH in experiments.
9. How does dilution affect the pH of an acid or base?
Dilution increases the pH of an acid and decreases the pH of a base by reducing the concentration of H+ or OH- ions.
- For acids, decreasing [H+] increases pH.
- For bases, decreasing [OH-] increases pOH and slightly lowers pH toward 7.
- For example, diluting HCl(aq) lowers its acidity and raises its pH.
10. What are common sources of error in the determination of pH experiment?
Common sources of error in the determination of pH experiment include improper calibration, contaminated electrodes, and temperature variations.
- Not calibrating the pH meter with buffer solutions.
- Dirty or dry glass electrode.
- Not rinsing the electrode between solutions.
- Changes in temperature affecting pH readings.
