January 21, 2023

Scientific Knowledge

“Learning is never done without errors.”

Class 10th CBSE – Science Practicals (Chemistry)

Class 10th CBSE – Science Practicals (Chemistry)?

Experiment No. 01

Aim:

To determine the pH of the given samples using pH paper or universal indicator. The samples whose pH has to be determined are-

  1. Dilute CH3COOH
  2. Dilute NaOH
  3. Salt NaCl
  4. Dilute NaHCO3
  5. Water
  6. Lemon juice

Materials required:

  1. Six test tubes
  2. Test tube holder
  3. Glass rod
  4. Measuring cylinder (10 mL)
  5. Dropper
  6. pH paper
  7. Standard pH colour chart
  8. Dilute acid CH3COOH
  9. Dilute base NaOH
  10. Salt NaCl (preparation: dissolve 1 gram salt in 10 mL distilled water)
  11. Water
  12. Lemon juice
  13. Dilute NaHCO3

Theory:

What is pH?

pH is a measure of hydrogen ion concentration to determine the alkalinity or acidity of a solution.

  • ./ If the pH value of a solution is less than 7 it is an acidic solution
    • .-If the pH value of a solution is greater than 7 it is a basic solution
    • . If the pH value of a solution is equal to 7 it is a neutral solution

What is pH scale?

The pH scale consists of values which range from 0 (very acidic) to 14 (very alkaline). The numbers on the scale help to determine the hydrogen ion concentration.

What is pH paper?

pH paper can help us know if a solution is basic, acidic or neutral. When the pH paper is dipped into a solution whose pH has to be determined, a colour will be developed. This colour is compared with the standard pH colour chart. Instead of pH paper, we can also use universal indicator paper or universal indicator solution.

pH value chart:

Class 10th CBSE - Science Practicals (Chemistry)
10th CBSE – Science Practicals (Chemistry)

Procedure:

  1. Wash six test tubes with distilled water and put them on test tube stand and label them A, B, C, D, E, F.
  2. Add 2ml of CH3COOH in test tube A, Add 2ml of NaOH in test tube B, Add 2ml of NaCl in test tube C, Add 2ml of NaHCO3 in test tube D, Add 2ml of Water in test tube E, Add 2ml of Lemon juice in test tube F.
  3. Take white tile, place 6 pH paper and label them A, B, C, D, E, F.
  4. Use a dropper or glass rod to put the respective sample solutions on the labelled pH paper placed on the white tile.
  5. Observe the colour change.

Observation:

SampleColour on pH paper
AOrange
BDark blue
CRed
DLight blue
EGreen
FPink

Result and Conclusion:

Test tubeSolutionpH colour paperpHNature
Sample ACH3COOHOrange3Weak acid
Sample BNaOHDark blue14Strong base
Sample CNaClRed1Strong acid
Sample DNaHCO3Light blue9Weak base
Sample EWaterGreen7Neutral
Sample FLemon juicePink2Weak acid

Precautions to be taken during the experiment

  • Use freshly prepared test sample for the experiment.
  • The fruit juice sample should also be fresh to get the proper pH values.
  • Glass rod or dropper used for one sample should be washed thoroughly before using it for the other samples.

Class 10th CBSE – Science Practicals (Chemistry)?

Viva Voce:

  1. Who was the first scientist to introduce pH?
    Ans: Soren Peder Lauritz Sorensen a Danish chemist.
  2. Define the pH of a solution.
    Ans: It is a measure of the basic or acidic power of a solution. It is a scale to measure the hydrogen ion concentration in the solution. Lower the hydrogen ion concentration higher is the pH.
  3. What is the pH of pure water at 25 °C?
    Ans: 7.
  4. There are two solutions with different pH values. Solution A has a pH value 6 and solution B has a pH value 5. Which solution is more acidic?
    Ans: Solution B whose pH value is 5 is more acidic.

10th CBSE – Science Practicals (Chemistry)

To determine the pH of the given samples using pH paper or universal indicator. The samples whose pH has to be determined?

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