Presentation on theme: "Acidity and Alkalinity How do we tell an acid from a base and what is it good for?"— Presentation transcript:
Acidity and Alkalinity How do we tell an acid from a base and what is it good for?
What is an acid? A substance that donates a hydrogen ion (proton) when dissolved in water. The hydrogen ion goes with water to make hydronium (H 3 O) It tastes sour
What is a base? A substance that accepts a hydronium ion (H 3 0) when in water. It releases hydroxide ions OH - when dissolved in water It tastes bitter Examples include: Ammonia, sodium hydroxide and baking soda What about bases make them react with acids to make salt?
Tomato is at 4 on the pH scale and lemon is at 2. How many times more acidic than tomato do you think the lemon is? 100times more! Each step on the pH scale works out to be 10 times more acidic or basic!
Indicators There are several substances which react with acids and bases They can tell us whether the substance is acidic or basic Examples include: litmus paper, bromothymol blue and red cabbage juice
Litmus paper Litmus paper is used to tell whether a solution is an acid or a base. It cannot tell you how strong the acid or base is It comes in 2 colours: red and blue Red paper turns blue in a base but will not change otherwise Blue paper turns red in an acid but will not change otherwise. Why do you think we sometimes need to test an acid or a base with both colours of paper before knowing what it is?
Bromothymol Blue Bromothymol Blue is a liquid that reacts in acids and bases It turns yellow in acid and blue in base It takes on a green tinge in a neutral solution It is good for telling the exact pH when the substance is only slightly acidic or basic
Red Cabbage Juice Red cabbage juice is another liquid indicator that will change colour in an acid or base It can be made by boiling red cabbage and keeping the juice It will change a wide range of colours and so can be used to accurately determine the aciditiy of a substance.
Classify each of the following as either an acid or a base