Use multiple indicators to determine whether a substance is an acid or a base.
Equipment:
- Four test tubes (or more depending on the chemicals being used.)- Test tube holder
- Various indicators - We used litmus paper (red or blue), universal indicator, cranberry juice etc.
- An acid - We used HCl
- A Base - We used NaOH
- A neutral substance - We used water
- A household "unknown" substance - We used toilet cleaner and Spray and Wipe
- Safety glasses - Don't be an idiot
Method:
- Add a few drops of each substance/chemical into each of your test tubes - Label or remember which one is which.
- Choosing an indicator test each substance. Either, add a few drops of universal indicator or cranberry juice or other liquid indicators into the chemicals/substances OR placing a strip of litmus paper into the tubes.
- Record the change. We used a table but it doesn't really matter.
- Using your results, determine whether your substances are acidic, basic, or neutral. With the universal indicator, use the colour to determine the pH level.
Results:
Discussion:
When we take acid and a base, such as sulfuric acid (H₂SO₄) and sodium hydroxide (NaOH), they begin to neutralise each other. If we start with a solution of sulfuric acid and universal indicator, the solution will begin as a reddish orange colour and a low pH level. As you add sodium hydroxide, the pH rises, approaching a pH of 7. The closer to this pH the solution gets, the more greenish-yellow the solution becomes. As all this is happening, OH⁻ particles are slowly connecting with and neutralising the H⁺ particles. Once a solid green, and completely neutralised, the solution will have a pH of 7 and the number of OH⁻ particles will be the same as the number of H⁺ particles. If you continue to add sodium hydroxide, the colour of the overall solution will become blue due to the OH⁻ particles outnumbering the H⁺ particles. The more unbalanced this is the more purple the solution will appear, leaving the solution with a pH of around 14.
If I were to do this experiment again, I'd remove the excess litmus paper, as it did not end up working at all. I would also use each indicator on all of the solutions, as it will give a more accurate result. In hindsight, I would have prefered if I did more investigation into what's happening in the experiment. (This would be things like what in each solution makes the indicators change colour etc.)
Hi please ignore the white litmus paper it was really useless
Conclusion:
From the results, we can confirm that hydrochloric acid is indeed an acid (Wow, incredible, such a revelation). We can tell this due to the fact it was a complete red in the universal indicator AND the red litmus paper stayed red. We can also confirm that sodium hydroxide is a base, due to its purple colour in the universal indicator and that water is neutral due to its green colour. As for the toilet cleaner and Spray and Wipe... These two were our unknowns. Again, from the chart, we can conclude that toilet cleaner is a weak acid, as it was orangey red in the universal indicator, and that Spray and Wipe is a base as it turned the red litmus paper blue. Remember, BLUE=BASE!
Discussion:
When we take acid and a base, such as sulfuric acid (H₂SO₄) and sodium hydroxide (NaOH), they begin to neutralise each other. If we start with a solution of sulfuric acid and universal indicator, the solution will begin as a reddish orange colour and a low pH level. As you add sodium hydroxide, the pH rises, approaching a pH of 7. The closer to this pH the solution gets, the more greenish-yellow the solution becomes. As all this is happening, OH⁻ particles are slowly connecting with and neutralising the H⁺ particles. Once a solid green, and completely neutralised, the solution will have a pH of 7 and the number of OH⁻ particles will be the same as the number of H⁺ particles. If you continue to add sodium hydroxide, the colour of the overall solution will become blue due to the OH⁻ particles outnumbering the H⁺ particles. The more unbalanced this is the more purple the solution will appear, leaving the solution with a pH of around 14.
Evaluation:
If I were to do this experiment again, I'd remove the excess litmus paper, as it did not end up working at all. I would also use each indicator on all of the solutions, as it will give a more accurate result. In hindsight, I would have prefered if I did more investigation into what's happening in the experiment. (This would be things like what in each solution makes the indicators change colour etc.)
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