Topic 4 - Chemical changes Flashcards
What is an acid?
A substance with a pH of less than 7, and forms H+ ions in water.
What is a base?
A substance with a pH greater than 7.
What is an alkali?
A base that dissolves in water to form a solution with pH >7 and forms OH- ions.
What is the reaction between acids and bases called, and what’s the equation?
1.Neutralisation
2.acid + base –> salt + water
What is the ionic equation for neutralisation?
OH- + H+ –> H2O
What colour does litmus turn to with alkalis and acids?
Alkalis - blue
Acids - red
What colour does phenophthalein turn to with alkalis and acids?
Alkali - pink
Acid - colourless
What colour does methyl orange turn to with alkalis and acids?
alkali - yellow
acid - red
What indicator should be used in titrations?
single indicators, such as phenolphthalein or litmus
Why do strong acids react faster than weak acids?
Strong acids have more H+ ions to react with other substances, so the rate of reaction is faster.
What makes a strong/weak acid?
1.Strong acids ionise fully in water, so all acid particles dissociate to release H+ ions.
2.Weak acids do not fully ionise in a solution, only a small proportion of acid particles dissociate to release H+ ions
What typre of reaction is the ionisation of a weak acid?
A reversible reaction between the undissociated and dissociated acid particles.
What do metal oxides/metal hydroxides form when reacting with an acid?
Acid + metal oxide/hydroxide –> Salt + Water
What happens when you add nitric acid + sodium hydroxide?
HNO3 + NaOH
nitric acid + sodium hydroxide –> sodium nitrate + water
HNO3 + NaOH –> NaNO3 + H2O
What do you get when you react sulfuric acid with pottasium hydroxide?
H2SO4 + 2KOH
Potassium sulfate + water
K2SO4 + 2H2O
What do acids and metal carbonates form after reacting?
acid + metal carbonate –> Salt + Water + Carbon dioxide
What happens when you react metal and acid?
acid + metal –> salt + hydrogen
How can we learn about a metal’s reactivity when we react it with an acid?
The more bubbles thay are released, the faster the reaction is going, the faster it is going the more reactive it is.
What does reacting a metal with water form?
metal + water –> metal hydroxide + hydrogen
What does a metals reaction with water tell us about it’s reactivity?
The more reactive a metal, the more it will react with water.
What is an electrolyte?
A molten or dissolved ionic compound.
What does cryolite do?
Lowers the melting point of aluminium oxide.
What happens at the cathode in an aqueous solution, when H+ ions and metal ions are present?
- If the metal ions form a metal more reactive than hydrogen, then hydrogen gas will be produced
- If the metal ions form a metal less reactive than hydrogen, then a solid layer of the pure metal will be produced.
What happens at the anode in an aqueous solution, when OH- ions and halide ions are present?
- If OH- and halide ions are present, then a halogen will be formed
- If there are no halides, then the OH- ions are discharged, and oxygen is formed.
