Acid + Base Salt + Water
According to this theory, I expect that the vinegar, which is an acid in the experiment, will be gradually neutralized by a base. When it is being neutralized, the pH will be higher, so I expect the color will change towards the neutral color of pH 7, which is green, then the pH will be higher again and gradually turns to purple, which presents a high pH.
Strongly Acidic Strongly Alkaline
pH1 pH14
Apparatus:
-
1 beaker of 100 cm3
- 1 measuring cylinder of 25 cm3
- 1 glass stirring rod
- 1 spatula
- 1 pH chart for Universal Indicator paper
- 1 pair of scissors
- 1 box of Universal Indicator paper
- 1 white tile
Chemicals:
- 500g of lime (Calcium hydroxide)
- 50ml of vinegar
- 50ml of water
Safety:
- Wear lab coats
- Put safety goggles on
- Beware of Calcium hydroxide which can irritate eyes
Procedure:
- Pour 20cm3 of vinegar into the beaker
- Add 20cm3 of water to the vinegar
- Stir the mixture with a glass rod
- Cut a piece of Universal Indicator paper into six strips
- Place the strips on a white tile
- Use the glass rod to place a drop of the vinegar solution on a strip of the indicator
- Add a spatula measure of lime to the beaker
- Stir the mixture
- Remove the glass rod
- Place a drop of the mixture on another strip of indicator paper
- Keep adding spatulas of lime until there is no further change in the colour of the indicator paper
Results:
Discussion:
What does the experiment show?
The experiment shows that the pH is getting higher and higher when more lime has been added. In a pH scale, the solution is getting more and more alkali when the pH is increasing. The more lime added, the more the acid is being neutralized. It comes to a point to the pH 7, which means the solution is neutral at that time. But when more lime is added, the neutral solution will change into alkali solution until to the optimum pH 14.
Why the results above don’t match with the recorded pH scale showing below the results?
The results have changed in a period of time after I have done the experiment. When I have just finished the experiment, the indicator is showing the pH of the drops of the solution and I have also taken the pH number according to the colours in the pH scales straight after the experiment is done. After a period of time, the chemical properties in the solution may change as it is in contact with the air, so the results showing above is not the exact results seen in the experiment.
Why the intervals of the pH each time are not the same even one spatula measure of lime is added every time?
Even one spatula measure of lime is added every time; there will be errors as we don’t weigh the amount of lime added every time. Also, we don’t know how much lime needed to move the pH by 1 every time.
Conclusion:
The experiment proves the change in the pH when a base is neutralizing an acid. The pH number is increasing when the neutralization takes place, because the solution is originally acidic, but turning to be neutral and then alkali, when a base is added.
The chart below shows a pH scale. In my previous results, the pH number is from the left side, which is red, but change of colours are moving to the right, turning to be neutral when lime has been added. When more lime is added, the neutral solution will have a higher pH number, turning to be alkali. The colour change is moving from the left to the right during neutralization, so the pH number is increasing. So the colours are turning from red to green, then green to purple.
Strongly Acidic Strongly Alkaline
pH1 pH14
Errors and Improvements: