Acids and Alkalis Flashcards
What is an acid
A substance that produces hydrogen ions in water
Has pH <7
What is an alkali
A substance that produces hydroxide ions in water
Has pH > 7
What has pH 7
A neutral substance
What is a base
A substance that reacts with an acid to produce a salt plus water
An alkali is a base
What is an indicator
A dye that changes colour depending on pH
Name 3 indicators and their colour changes
Litmus - red in acid, purple neutral, blue in alkali
Methyl orange - red in acid, yellow in neutral/alkali
Phenolphthalein - colourless in acid and neutral, pink in alkali
What is neutralisation
The reaction between an acid and base (alkali)
Produces a salt plus water
H+ + OH- = H20
At pH 7 number of H+ ions equals number of OH- ions
How would you investigate the neutralisation reaction between calcium oxide (a base) and dilute hydrochloric acid
- Measure set volume of acid into conical flask
- Measure fixed mass of Calcium oxide using mass balance
- Add Calcium oxide to acid
- Wait for base to completely react then measure pH with pH probe or universal indicator paper
- Repeat steps 2-4 until all acid has reacted - you know this as unreacted Calcium oxide will sit at bottom of flask
- Plot graph of pH against mass of base added
p105 revision book
What dose an acid ionises mean
An acid ionises or dissociates in water into H+ ions and another ion
eg HCl goes to H+ and Cl-
What is a strong acid
An acid that ionises almost completely in water ie most of the acid dissociates. Have very low pH <2
What is a weak acid?
An acid that only partly ionises in water only some dissociates to release H+. Have pH 2-6
What is a reversible reaction
One which can go both ways and set up an equilibrium eg weak acid dissociates but can reassociate
Is a strong acid a concentrated acid
