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Acids, bases and litmus paper

Acids, bases and litmus paper. Litmus paper is an ‘indicator’ that tells us whether a substance is acidic, basic or neutral. Blue litmus paper turns red in when put in an acidic substance. Red litmus paper turns blue when put in a basic substance.

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Acids, bases and litmus paper

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  1. Acids, bases and litmus paper • Litmus paper is an ‘indicator’ that tells us whether a substance is acidic, basic or neutral. • Blue litmus paper turns red in when put in an acidic substance. • Red litmus paper turns blue when put in a basic substance. • If you put both red and blue litmus paper in a substance and there is no change in colour, it is said to be ‘neutral’.

  2. Litmus paper

  3. Instructions • In your newly assigned groups get 1 test-tube rack, 3 test-tubes, a small beaker, and a bottle of HCl and NH4OH and make a station around the room. • When one of the natural indicators are free, one of you come to the front with your small beaker and get some of the natural indicator. • Go back to your station and pour 1/3 of the natural indicator in each test-tube. • Add acid to one test-tube, Base to another and water to the last. • View and compare the change in colours (if any!). • Create your own table to record the data! (however you like).

  4. Copy and complete the table

  5. Copy notes • pH is the measure of the concentration H+ ions in an aqueous (containing water) solution. • pH is a numerical measure from 0-14, where 0-6.9 is acidic, 7 is neutral and 7.1-14 is basic or alkali. • If a substance forms H+ ions in a solution it is acidic, and if it forms hydroxide OH- ions it is basic. • Extension: To calculate the pH we use the formula “–log(H+)” • E.g. for dilute HCl the concentration of H+ ions is 1X10-1 so using your calculator… pH = -log (1 exp -1) Therefore, pH = 1

  6. Questions to consider • What is the range of pH for the shampoos? • Are there any shampoos outside the range recommended by the textbook on page 246? • Why wouldn’t you use soap as a shampoo? • What is the pH of some of the indigesion powders? • Why? (what would it do in our body)? • Extension: ENO is also an indigestion powder, however it has a far different pH then other indigestion powders. Why could this be?

  7. Copy an complete the table

  8. Answers

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