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

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.

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

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

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 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14

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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.

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

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

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?