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Physical Science Notes 416-436
pH Lab
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Use for the pH scale

pH lab (the non-idiot proof lab)

 

Synthetic indicators:

            -Synthetic indicators are indicators that are made in a lab

e.g.: Universal (used in this lab), Bromothymol Blue (BTB) etc.

 

Natural indicators:

-Natural indicators are indicators that are from nature. They can also be called household indicators.

e.g.: Cabbage juice (used in this lab), Flowers etc.

 

In this lab you had to make your own natural indicator from cabbage leaves. This is the procedure to make it:

 

1) Take some cabbage

2) Add a little bit of water

3) Heat up the cabbage and water

4) Obtain the juice

 

The reason you add only a bit of water is because you want to have the most concentrated cabbage juice as possible. You want it to be as dark as you can get it, by adding to much water it dilutes it to much.

 

-In this lab 12 chem. plate circles were filled with different pHs. It started with pH 2 and went up to pH 12. Once that the pHs were in their circles a drop of universal indicator was added to each different pH and the colours were recorded.

-Those steps were repeated, but instead of using universal the second time we used cabbage juice as our indicator.

 

Observations:

The chart below tells you what colour was shown when indicators were added:

pH

level

Synthetic indicator: Universal

Natural indicator:

Cabbage

pH2

Red

Fuscia

pH3

Red

Fuscia

pH4

Red

Purple-pink

pH5

Orange

Purple

pH6

Yellow

Purple

pH7

Light-green

Blue

pH8

Green

Blue-green

pH9

Turquoise

Green

pH10

Purple

Green

pH11

Dark purple

Green

pH12

Deep purple

Grass green

 

The picture below shows the colours shown when the indicators were added. All pH liquids started off being clear.

phlabscale.jpg

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