EXPERIMENT: Finding the pH of Various Samples Using pH Paper/Universal Indicator

---

AIM:

To find the pH value of the following samples using pH paper/universal indicator:

• Dilute Hydrochloric Acid (HCl)
• Dilute Sodium Hydroxide (NaOH) solution
• Dilute Ethanoic Acid (CH₃COOH) solution
• Lemon juice
• Water
• Dilute Sodium Hydrogen Carbonate (NaHCO₃) solution

---

MATERIALS REQUIRED:

1. Test tubes (6)
2. Test tube stand
3. pH paper/Universal indicator
4. pH color chart
5. Glass rod
6. Dropper
7. White tile
8. Samples: Dilute HCl, Dilute NaOH, Dilute Ethanoic Acid, Lemon juice, Water, Dilute NaHCO₃ solution

---

THEORY:

pH (Potential of Hydrogen): It is a scale used to measure the acidity or basicity of a solution. The pH scale ranges from 0 to 14.

• pH < 7 → Acidic solution
• pH = 7 → Neutral solution
• pH > 7 → Basic/Alkaline solution

Universal Indicator/pH Paper: These are chemical indicators that show different colors at different pH values. By comparing the color with a standard pH color chart, we can determine the approximate pH of the solution.

Nature of Solutions:

• Strong Acids (like HCl): pH 0-3
• Weak Acids (like CH₃COOH, citric acid in lemon): pH 4-6
• Neutral (like pure water): pH 7
• Weak Bases (like NaHCO₃): pH 8-10
• Strong Bases (like NaOH): pH 11-14

---

PROCEDURE:

1. Take six clean and dry test tubes and label them as A, B, C, D, E, and F.
2. Pour about 2-3 mL of the following solutions into respective test tubes:
   • Test tube A: Dilute HCl
   • Test tube B: Dilute NaOH solution
   • Test tube C: Dilute Ethanoic Acid
   • Test tube D: Lemon juice
   • Test tube E: Water
   • Test tube F: Dilute NaHCO₃ solution
3. Cut small strips of pH paper (or use universal indicator solution).
4. Using a clean glass rod, put a drop of solution from test tube A on a pH paper strip placed on a white tile.
5. Observe the color change immediately and compare it with the standard pH color chart.
6. Note the pH value.
7. Repeat steps 4-6 for all other test tubes (B to F).
8. Record your observations in the observation table.

---

OBSERVATION:

S. No.	Solution	Color of pH Paper	pH Value	Nature of Solution
1	Dilute HCl	Red	1-2	Strong Acid
2	Dilute NaOH solution	Blue/Purple	12-13	Strong Base
3	Dilute Ethanoic Acid	Orange/Yellow	4-5	Weak Acid
4	Lemon juice	Orange	2-3	Acidic
5	Water	Green	7	Neutral
6	Dilute NaHCO₃ solution	Light Blue	8-9	Weak Base

(Note: Actual pH values may vary slightly depending on concentration)

---

RESULT:

The pH values of the given solutions are determined using pH paper/universal indicator:

• Dilute HCl is strongly acidic (pH ~1-2)
• Dilute NaOH is strongly basic (pH ~12-13)
• Dilute Ethanoic Acid is weakly acidic (pH ~4-5)
• Lemon juice is acidic (pH ~2-3)
• Water is neutral (pH ~7)
• Dilute NaHCO₃ is weakly basic (pH ~8-9)

---

PRECAUTIONS:

1. Use clean and dry test tubes and glass rods to avoid contamination.
2. Do not dip the pH paper directly into the solution; use a glass rod to transfer a drop.
3. Compare the color of pH paper immediately as the color may fade with time.
4. Use dilute solutions to avoid skin contact and ensure safety.
5. Handle acids and bases carefully; wear safety goggles if available.
6. Do not taste or smell any chemical solution.
7. Use a fresh strip of pH paper for each solution.
8. Dispose of chemicals as per laboratory guidelines.