UNIT 1 ACIDS ALKALIS CHEMICAL REACTIONS Lesson 2

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

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

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

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

p. H SCALE We can compare the colour of the p. H paper to the p. H scale to find out how strong or weak an acid or alkali is. NEUTRAL STRONG ACID p. H 0 1 2 WEAK ACID 3 4 5 6 WEAK ALKALI 7 8 9 STRONG ALKALI 10 11 12 13 14

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

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

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

Check Test 1. What similarities are there when using p. H paper and universal indicator? 2. What differences are there when using p. H paper and universal indicator? 3) Can you think of any occasion when neither method would be suitable?