4c. Cabbages, Acids, and Bases!!

The Experiment

In this experiment we had to determine the identity of two unknown solutions. We had to figure out if they were weak or strong acids or bases or neutral solutions. To do this we cut up some red cabbage and put it in a beaker with water just covering it. Then we  boiled it so that the juice from the cabbage went into the water. We then strained the cabbage out, leaving only a purplish liquid, an indicator. We put the indicator in the different liquids- a strong acid, a weak acid, a strong base, a weak base and a neutral liquid. We knew that acidic liquids turn red, basic liquids turn greenish-yellow and neutral liquids turn purple or blue. From this knowledge we could determine the identity of the two mystery liquids.

The liquids and their colours

Pure water- blue

Weak acid- pink

Strong acid- red

Weak base- turquoise

Strong base- yellow

Determining the identities of two unknown solutions

Solution 1: This liquid is blue, meaning it is neutral.

Solution 2: This liquid is yellow, meaning it is a strong base

How many times stronger would an  acid with ph1 be compared to the acid with a  pH of 3?

An acid with a pH of 1 is 100 times stronger than  an acid with a pH of 3. This is because each pH number is separated by ten times more strength. For example, an acid with a pH of 1 is 10 times stronger than an acid with a pH of 2 and an acid with a pH of 2 id ten times stronger than an acid with a pH of three 3.

4b. Neutralizing Acids and Bases

The Experiment

For this experiment we had a few drops of indicator in a beaker and we had to put in some acidic liquid and neutralize it. Then we did the same again but witha  basic liquid.

Neutralizing an acid

To neutralize an acid that had a pH of 1, we added some basic liquid to it and kept adding a few drops of each liquid until it was a brownish liquid with a pH of about 7, meaning neutral.

Here is a pucture of the acid that we neutralized:

Neutralizing a base

To neutralize a base with a pH of 14, we added some acidic liquid to it and kept adding drops of the two liquids until it too was a brown colour with a pH of 7 too.

4a. Acids and Bases

The pH scale

This is the pH scale which determines how acidic or basic various liquids are. It oes from 0 to 14. A pH of 7 is neutral,  a pH less than 7 is acidic and a pH greater than 7 is basic. Here is a picture of the ph scale with some examples for each number.

The experiment

For this experiment we put pieces of pH paper in a dish with little bowls in it and then added 13 liquids, 1 for every piece of paper. We mannaged to find out how acidic or basic the liquid was by looking at the colour the pH paper turned when the chemical was added. If it went blue or green it was basic whereas oranges and reds were more acidic (see the pH scale above.)

Liquids and their place on the pH scale

1. Pure water- 6
2. Tap water- 9
3. Drain cleaner- 14
4. Soap- 6
5. Vinegar- 2
6. Orange juice- 3
7. Coke- 2
8. Baking soda- 9
9. Stomach/hydrochloric acid- 1
10. Ammonia- 12
11. Vitamin C- 2
12. Milk- 6
13. Lemon juice- 1.5
14. Spit- 6

Which substance given is the most acidic?

The stomach/hydrochloric acid was the most acidic liquid.

Which substance is the most basic?

The drain cleaner was the most basic liquid.

3b. Rates of Reaction

What is a catalyst?

A catalyst is a substance of any kind that speeds up or slows down a chemical reaction without itself being affected. They can be organic, synthetic or metal. The process by which the catalyst speeds up or slows a reaction is called catalysis.

Determine which food group (liver, celery, potato, bread) is the best and the worst catalyst for the decomposition of hydrogen peroxide.

Out of the four foods we tested, liver , celery, potato and bread, the liver proved the most successful at decomposing  the hydrogen peroxide. When the acid came into contact with it, it fizzed up and came up the test tube and bubbles came right out the top! The potato  was the second most effective, then the celery and finally the bread.

The Decomposition of hydrogen peroxide

When hydrogen oxide is decomposed it turns into oxygen and water. If a glowing splint is put into the test tube with liver and hydrogen peroxide so that it isn’t touching them but is still in the test tube, the oxygen will cause it to be re-lit!

3a. Rates of Reaction

How does concentration affect the speed of the reaction?

If there is a higher concentration of a given substance the chemical reaction is quicker. The experiment we did to test this was to add calcium carbonate rocks to hydrochloric acid. In one test tube we had 5ml of acid and in the other we had 7ml of acid. The result was that the one in the 7ml of hydrochloric acid dissolved faster than the other one with only 5ml of acid.

How does surface area affect the speed of the reaction?

A larger surface area provides a quicker reaction. The experiment we did to test this was to take 1 teaspoon of calcium carbonate powder and add it to 5 ml of htdrochloric acid in a test tube and take a rock (which had a smaller surface area) and add that to 5ml of acid in a different test tube. Even when the powder had finished reacting, the rock was still fizzing away. The powder, with the larger surface area, had a much faster reaction.

How does temperature affect the speed of the reaction?

we found that the colder the liquid is, the faster the reaction occurs. The experiment we conducted in order to test this was heating up one test tube with 5ml of hydrochloric acid in a beaker of water and keeping the other test tube, also with 5ml of acid, cold. The hot one was 30 degrees Celsius and the cold one was 25 degrees Celsius.  Then we added a teaspoon of  calcium carbonate powder to each test tube and the cold one reacted quicker. We were very surprised by our results and when we asker our teacher, she said that our results were incorrect and that in fact, the hot one should have reacted faster.

Detailed question-

How does concentration affect the speed of the reaction?

Observations and results

• Both acids fizzed immediately when the acid was put in to them.
• They both became a white liquid that looked a bit like milk after the fizzing had stopped.
• The more concentrated acid had a faster reaction.
• All three trials had similar results.

Data

In the table below is the data from our experiment

 

Conclusion

My hypothesis was that the more concentrated liquid would have the fastest reaction because I thought that the more acid there was, the quicker the powder would dissolve. If the acid was diluted, there would not be as much of it to help dissolve the powder. This proved correct as the 10ml of acid only took an average of  14.3 seconds to finish reacting whereas the diluted acid, with 5ml of acid and 5ml of water, took an average of 22.6 seconds to finish reacting. I think we got these results because of the reason I stated above, that the more acid there is to help dissolve  the powder, the quicker the reaction is.

Some errors that were in this experiment were the following:

• The timing was not very accurate. We used stopwatches and probably did not start at exactly the right time or stop at the right time. It was quite hard to see when to stop because you could not always see the bubbles because it was a white liquid and hard to see. This would have affected our results.
• Our measurements might not have been completely accurate every time. We tried to use the same amount of powder each time- 1 flat teaspoon full- but it would still have varied slightly from time to time.

If we re-did this experiment, there would be several things that we would change to make this experiment more accurate. First of all, we would need to make the timing more accurate. This would be challenging because it is so hard to see the bubbles in the white liquid and to determine when the reaction is over. This could be achieved by videoing the experiment and then watching it in slow motion sso that we could determine the exatc time it took the reaction o take place. Secondly, we would need to make sure we always had the same amount of calcium carbonate powder. We could do this by weighing it instead of measuring it out in a teaspoon. Finally, we could do a bigger experiment with more trials so that we would have more data to draw a more accurate conclusion. All of these would make the experiment much more accurate.