Testing Weak and Strong Laboratory Acids and Alkalis with Indicators

Testing Weak andStrong Acid and Alkalis with indicators :

Objective: Hazcard : 47A-91A-6-40A

To determine the pH levels of different acids and alkalis (HCl, NaOH, NH₃, CH₃CH₂OH) using a universal indicator and other pH indicators. Also, to observe and record the colors of the solutions on a pH chart.

Materials:

• Hydrochloric acid (HCl) – strong acid 0.1 M to 1.0 M

• Sodium hydroxide (NaOH) – strong alkali 0.1 M to 1.0 M

• Ammonia (NH₃) – weak alkali 0.1 M to 0.5 M

• Ethanol (CH₃CH₂OH) – neutral substance Pure or 70%(v/v) solution

• Ethanoic acid (CH3COOH) 0.1 M to 1.0 M

• Universal indicator solution or pH paper

• Spotting tiles

• Other indicators (litmus paper, phenolphthalein, methyl orange....)

• Droppers/pipettes

• pH chart

• Coloured pens/pencils to colour a pH chart

• Distilled water (for dilutions if needed)

• Safety goggles and gloves

Method:

1. Set Up:

   • Place a spotting tile in front of you with enough wells for each substance.

   • Label the wells for each solution: HCl, NaOH, NH₃, CH₃CH₂OH.

2. Adding the Solutions:

   • Using a dropper or pipette, carefully place a few drops of each solution into its respective well on the spotting tile.

3. Testing with Universal Indicator:

   • Add a drop of the universal indicator to each solution.

   • Observe the colour change and compare it with the pH chart.

   • Record the pH values and colours observed for each solution.

4. Testing with Other Indicators:

   • Repeat the test for each solution using different indicators (e.g., litmus paper, phenolphthalein, methyl orange).

   • Record the colour changes and note whether the solution is acidic, alkaline, or neutral based on the indicator used.

5. Colouring the pH Chart:

   • Based on your observations, use coloured pens/pencils to mark the pH values for each solution on a blank pH chart (ranging from 1 to 14).

Expected Results:

• HCl (Strong Acid):

  • Universal indicator: Red (pH ~1-2)

  • Litmus: Red

  • Phenolphthalein: Colourless

  • Methyl orange: Red

• NaOH (Strong Alkali):

  • Universal indicator: Purple/Blue (pH ~12-14)

  • Litmus: Blue

  • Phenolphthalein: Pink/Magenta

  • Methyl orange: Yellow

• NH₃ (Weak Alkali):

  • Universal indicator: Blue/Green (pH ~9-10)

  • Litmus: Blue

  • Phenolphthalein: Faint pink

  • Methyl orange: Yellow

• CH₃CH₂OH (Neutral/Weakly acidic substance):

  • Universal indicator: Green (pH ~7)

  • Litmus: No significant change

  • Phenolphthalein: Colourless

  • Methyl orange: Orange

Safety Notes:

• Always wear safety goggles and gloves when handling acids, alkalis, and indicators.

• Handle the strong acid (HCl) and alkali (NaOH) with care to avoid skin irritation or chemical burns.

Conclusion:

By using universal indicators and other chemical indicators, you can effectively determine the pH and relative strength of acids and alkalis. Strong acids and alkalis show more extreme pH values, while weak acids/alkalis and neutral substances show intermediate or neutral pH levels.