11/04/13

 Can you give an example of a strong acid, what would its pH value be?  Do you think citrus acid found in fruits is a strong acid, what do you think its pH value is?  Do you know any strong bases what would its Ph would be?  Give an example of a weaker base and estimate its pH

 The Arrenhius definition of an acid and a base and further a strong acid/base and weak acid/base  The Bronsted- Lowry definition of an acid and base  The pigment found in plants and an example of an indicator that uses this pigment  Why this pigment can act as a natural indicator  How to prepare a natural indicator using red cabbage

 The Arrenhius Definition:  An Acid is a substance that dissociates in water to produce H + ions.  HCl → H + + Cl -  HNO 3 → 2H + + NO 3 -  A strong acid is one which dissociates almost completely in water to give H + ions such as HCl.  A weak acid is one which dissociates only partially in water to give H + i.e. ethanoic acid.

 A Base is a substance that dissociates in water to produce OH - ions.  NaOH → Na + + OH -  Mg(OH) 2 → Mg OH -  A strong base is one which dissociates almost completely in water to give OH - i.e. NaOH  A weak is one which only partially dissociate in water i.e. Mg(OH) 2

 An Acid is a proton donor, i.e. donates a proton.  A Base is a proton acceptor, i.e. accepts a proton.  HCl + H 2 O → H 3 O + + Cl -  The HCl has donated a proton to water, therefore it is an Acid. Since the molecule of water accepts the proton, it is the Base.

 NH 3 + H 2 O → NH OH -  What does this tell us about water?

 It is clear from the reaction of Water with HCl and NH 3 that water can act as either an Acid or a Base.  A substance that can do this is said to be Amphoteric (the greek word for on both sides!)

 Many indicators we use today such as Phenolpthalein indicator and Methyl orange indicator are derived from natural plant materials such as red cabbage, blackberries, blueberries and beet plants.  All these plants contain a pigment molecule called an Anthocyanin, the active ingredient used in indicators.  They are water soluble and acts as Indicators by changing colour in different Ph’s.

 Is food in the cell vacuole in plants but also in the leaves, stems and roots  The natural occurring colour of the pigment in most plants is a red-purple colour  In flowers bright reds and purples are adaptive for attracting pollinators  There are also know to protect the plant cells from high-light damage by absorbing ultraviolet light.

 Contains the pigment molecule Anthocyanin and works as a natural indicator by changing colour when solutions of different pH’s are added.  pH: 2, 4, 6, 8, 10, 12  Colour: Red,Purple,Violet,Blue,Blue-Green, Greenish yellow

 Place about 2 cups full of red cabbage in a blender, cover it with boiling water and blend!  The water used should be deionised water.  The liquid should be at around pH 7 after blending  Pour about ml of the indicator into each beaker.  Add the 4 unlabelled solutions to the indicator until a colour change is detected.  Isolate the unlabelled solutions by the colour changes that occur!

 Repeat the procedure using blue grapes which also contains the Anthocyanin pigment.  Compare the results which indicator works best and is the most accurate.