acidity and alkalinity
DESCRIPTIONAcidity 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?. - PowerPoint PPT Presentation
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 (H3O)
• It tastes sour
What is a base?
• A substance that accepts a hydronium ion (H30) 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!
• 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 is a liquid that reacts in acids and bases
• It turns yellow in acidand 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 byboiling 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
Bibliography of images• http://science.nayland.school.nz/SimonPa/Webpage/Year10/Acid_base_images/acids
/images/crm3s3_1.jpg• http://www.biologycorner.com/resources/dissociation.gif• http://oldwww.mtlsd.org/senior/science/JPtachcinski/Lab_Proc/Basic%20Science%20
Lab%20Techniques_files/litmus.jpe• http://www.farm.ucl.ac.be/tpao/instrumentation/titrimetrie/Indicateurs/HBtB.jpg• http://www.erowid.org/archive/rhodium/chemistry/equipment/pictures/ph-cabbage.jpg• http://wetheadmedia.com/wp-content/uploads/pictures/2009/03/Arm-Hammer-Baking-
Soda.jpg• http://cojent7.files.wordpress.com/2010/05/coca-cola.jpg• http://www.bized.co.uk/images/battery.jpg• http://beautifullyused.com/wp-content/uploads/2009/03/lemon.jpeg• http://www.mochadad.com/wp-content/uploads/2008/12/soap-on-a-rope.jpg• http://www.savingwithshellie.com/wp-content/uploads/2009/04/ammonia.jpg