Acids, bases and litmus paperAcids, bases and litmus paper

Litmus paper is an ‘indicator’ that tells us Litmus paper is an ‘indicator’ that tells us whether a substance is acidic, basic or neutral.whether a substance is acidic, basic or neutral.

Blue litmus paper turns red in when put in an Blue litmus paper turns red in when put in an acidic substance.acidic substance.

Red litmus paper turns blue when put in a basic Red litmus paper turns blue when put in a basic substance.substance.

If you put both red and blue litmus paper in a If you put both red and blue litmus paper in a substance and there is no change in colour, it is substance and there is no change in colour, it is said to be ‘said to be ‘neutralneutral’.’.

Litmus paperLitmus paper

InstructionsInstructionsIn your newly assigned groups get 1 test-tube rack, 3 In your newly assigned groups get 1 test-tube rack, 3 test-tubes, a small beaker, and a bottle of HCl and test-tubes, a small beaker, and a bottle of HCl and NHNH44OH and make a station around the room. OH and make a station around the room.

When one of the natural indicators are free, one of you When one of the natural indicators are free, one of you come to the front with your small beaker and get some come to the front with your small beaker and get some of the natural indicator.of the natural indicator.Go back to your station and pour 1/3 of the natural Go back to your station and pour 1/3 of the natural indicator in each test-tube. indicator in each test-tube. Add acid to one test-tube, Base to another and water Add acid to one test-tube, Base to another and water to the last.to the last.View and compare the change in colours (if any!).View and compare the change in colours (if any!).Create your own table to record the data! (however Create your own table to record the data! (however you like).you like).

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Natural Indicator

Acid (HCl) Water (H2O) Base (NH4OH)

Ammonium Hydroxide

Green Tea

Black Tea

Onion Skins

Boysenberry Juice

Red Cabbage Juice

Copy notesCopy notespH is the measure of the concentration H+ ions in an pH is the measure of the concentration H+ ions in an aqueous (containing water) solution.aqueous (containing water) solution.pH is a numerical measure from 0-14, where 0-6.9 is 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.acidic, 7 is neutral and 7.1-14 is basic or alkali.If a substance forms H+ ions in a solution it is acidic, If a substance forms H+ ions in a solution it is acidic, and if it forms hydroxide OH- ions it is basic.and if it forms hydroxide OH- ions it is basic.Extension: To calculate the pH we use the formula “–Extension: To calculate the pH we use the formula “–log(H+)”log(H+)”E.g. for dilute HCl the concentration of H+ ions is E.g. for dilute HCl the concentration of H+ ions is 1X101X10-1-1 so using your calculator… so using your calculator…pH = -log (1 exp -1) pH = -log (1 exp -1) Therefore, pH = 1Therefore, pH = 1

Questions to considerQuestions to consider

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

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Name Formula IonsSulfuric acid

Hydrochloric acid

Sodium Hydroxide

Ammonium Hydroxide

Ammonium Nitrate

Acetic acid CH3COOH

AnswersAnswers

Name Formula IonsSulfuric acid H2SO4 H+ SO4

2-

Hydrochloric acid HCl H+ Cl-

Sodium Hydroxide NaOH Na+ OH-

Ammonium Hydroxide NH4OH NH4+ OH-

Ammonium Nitrate NH4NO3 NH4+ NO3-

Acetic acid CH3COOH H+ CH3COO-

Ammonia and Water NH3 H2O NH4+ OH-