1. UNIT 1 ACIDS, ALKALIS & CHEMICAL REACTIONS Lesson 2 – pH paper

2. Aims of the Lesson I know how to use pH paper when testing a solid.
I can compare the colour of pH paper to a colour chart to predict the pH of a substance.

3. ACID OR ALKALI? Last time we used green universal indicator solution.
Do you remember that we can add chemicals called INDICATORS to a substance to find out if it is acid or alkali?
Last time we used green universal indicator solution.
Today we will use pH paper not universal indicator.
UNIVERSAL INDICATOR
pH PAPER

4. pH PAPER pH paper turns: Orange/Red with acids
Blue/Purple with alkalis
Green/Yellow with neutral substances (neither acid nor alkali)

5. pH SCALE
We can compare the colour of the pH paper to the pH scale to find out how strong or weak an acid or alkali is.
NEUTRAL
STRONG ACID WEAK ACID WEAK ALKALI STRONG ALKALI pH

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7. MEASURING pH with pH paper
1. Collect a dimple tile
2. Collect pH paper and a dropper
3. Add spatulaful of sample to dimple tile and dropper water over the top
4. Place a piece of pH paper into dimple and compare pH to chart.

8. MEASURING pH with paper
Copy this table in to your jotter and complete as you carry out the experiment:
SOLUTION
Colour pH
ACID or ALKALI or NEUTRAL
Example
RED 3
Acid
Sodium Bicarbonate
Ammonium Chloride
Ammonium Nitrate
Sodium Chloride
Zinc carbonate
Sodium carbonate

9. Acids have pH values of _____. They turn pH paper ________________.
Copy and complete this SUMMARY:
Acids have pH values of _____. They turn pH paper ________________.
Alkalis have pH values of _____.
They turn pH paper ___________.
Neutral solutions have a pH value of ___. They turn pH paper ______.
0-6
orange / red
8-14
blue 7
Yellow

10. Check Test
What similarities are there when using pH paper and universal indicator?
What differences are there when using pH paper and universal indicator?
3) Can you think of any occasion when neither method would be suitable?