Topic 4: Acids and alkalis flashcards
Which ions make aqueous solutions acidic?
Hydrogen ions (H+)
Which ions make aqueous solutions alkaline?
Hydroxide ions (OH-)
What is the definition of a strong acid?
Strong acids fully ionise in aqueous solutions
What is the definition of a weak acid?
Weak acids partially ionise in aqueous solutions
What is the pH scale?
The pH scale ranges from pH 0 to pH 14 and measures the acidity or alkalinity of a solution.
What are pH ranges for acids and alkalis? What is the pH of a neutral solution?
Acid - Less than pH 7 (pH 1 is strongest).
Neutral - pH 7.
Alkali - Greater than pH 7 (pH 14 is strongest).
What can be used to measure pH?
Universal indicator
pH probe
What colour us phenolphthalein in acid and alkali?
Acid - Colourless
Alkali - Pink
What colour is methyl orange in an acid and an alkali?
Acid - Red
Alkali - Yellow
What colour is blue litmus paper in an acid and an alkali?
Acid - Turns red
Alkali - Stays blue
What colour is red litmus paper in an acid and an alkali?
Acid - Stays red
Alkali - Turns blue
Suggest a problem with using universal indicator to test the pH of a solution
The colour of the solution is matched to a pH colour chart. This is quite subjective as people may disagree with which colour the solution matches.
It doesn’t provide an exact pH value.
Acid X has a pH of 1. What can you say about the concentration of hydrogen ions in acid X? (higher only)
There is a high concentration of hydrogen ions in the acid, making it a strong acid.
The lower the pH of the acid, the higher the concentration of H+ ions.
Alkali Y has a pH of 8.5. What can you say about the concentration of hydroxide ions in alkali Y? (higher only)
There is a low concentration of hydroxide ions in the alkali, making it a weak alkali.
The lower the pH of the alkali, the lower the concentration of OH- ions.
If pH decreases by one unit, what happens to the concentration of hydrogen ions? (higher only)
The hydrogen ion concentration increases by a factor of 10.
