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pH and Indicators

Derivation of pH, Uses of indicators

QuestionAnswer
What is the breaking up of water into H+ and OH- ions known as? The self ionisation of water
What is Kw the symbol for? The Ionic Product of Water
What Danish chemist discovered the pH scale? Soren Peter Sorensen
Definition of pH? The pH of a solution is the negative log to the base 10 of the hydrogen ion concentration measured in moles per litre.
What do the letters "pH" actually stand for? It comes from the German word "potenz" meaning power
What is Ka the symbol for? What does it tell us? The Acid Dissociation Constant. It tells us how strong an acid is by telling us how much an acid dissociates. Strong acids have a large Ka
What is Kb the symbol for? What does it tell us? The Base Dissociation Constant. It tells us how strong a base is by telling us how much it dissociates. Strong bases have a large Kb
What is the relationship between acids and conjugate bases? Strong acids make weak conjugate bases, weak acids make strong conjugate bases.
What formula is used to calculate the pH of a substance? -log^10[H+}
How do we calculate the pH of a base? We use -log^10[H+} then take the answer away from 14 to get the number of OH- ions.
How do we calculate the pH of weak acids and bases? We use the formula (square root)Ka x Mol(acid) to get the concentration of H+ ions. We then sub this value into -log^10[H+}
What range do most indicators need to show a distinct colour change? A change of 2 units are required to show a colour change
What is the range and colour change of Methyl Orange? 3-5 Red to Yellow
What is the range and colour change of Litmus? 5-8 Red to Blue
What is the range and colour change of Phenolphthalein? 8-10 Colourless to Pink
What is the correct indicator for a strong acid vs a weak base? All 3 indicators, Methyl Orange, Litmus and Phenolphthalein will work for this titration. The range of the titration is from 3-10
What is the correct indicator for a strong acids and a weak base? The range here is from 3-7 so Methyl Orange will be a suitable indicator
What is the correct indicator for a weak acid and a strong base? The range here is from 7-10 so Phenolphthalein will be a suitable indicator
What is the correct indicator for a weak acid and a weak base? The range for this titration is extremely small and cannot be detected by an indicator. Instead we would titrate the weak acid against a strong base and the weak base against a strong acid.
Created by: cbschemistry