topic 4 Flashcards
What is an indicator
a dye that changes colour depending on whether its above or below a certain pH
What can be used to measure the pH electronically
A pH probe attached to a pH meter
What is an acid
A substance that forms aqueous solutions with a pH of less than 7
What is a base
A substance with a pH greater than 7
Acid + base ——>
Salt + water
What ions do alkalis form in water
OH^-
What ions do acids form in water
H^+
What do acids do in water
- They ionise in aqueous solution
- they produce protons in water
What type of acids ionise completely in water
Strong acids
Weak acids do not fully ionise in solutions what does this mean for some acid particles
They dissociate to release H^+ ions
What is an electrolyte
A molten or dissolved ionic compound
What happens in electrolysis
An electric current is passed through an electrolyte
What do ions do in electrolysis
They move towards the electrodes, where they react, and the compound DECOMPOSES
What do positive ions do in the electrolyte
Move towards the cathode (-ve electrode) and gain electrons (they are REDUCED)
What type electrode do positive ions move towards
-ve electrode
What do the negative ions do in the eoectrolyte
Move towards the anode (+ve electrode) and lose electrons (they are OXIDISED)
What type of electrode do the negative ions move towards
+ve electrode
As ions travel to the electrodes what happens
It creates a flow of charge through the electrolyte
What happens as ions gain or lose electrons
They form the uncharged element and are discharged from the electrolyte
Why can’t an ionic solid be electrolysed
Because the ions are in fixed positions and can’t move
Why can molten ionic compounds be electrolysed
Because the ions move freely snd conduct electricity
What type of ionic compound can be electrolysed
Molten ionic compound
Positive METAL ions are … to the element at the …
- reduced
- cathode
Negative NON-METAL ions are …. to the element at the …
- oxidised
- anode
What method is used if a metal is “too reactive to be reduced with carbon or reacts with carbon”
Electrolysis
What is the main draw back of electrolysis and why
It is expensive as lots of energy is required to melt the ore and produce the required current
What ore is aluminium extracted from
Bauxite by electrolysis
What dies bauxite contain
Aluminium oxide (Al2O3)
What is electrolysis
- Extracting metal using electricity
- the ore is melted to produce the required current
As aluminium oxide has a high melting temperature what is it mixed with
Cryolite to lower the melting point
In aluminium oxide what dies the molten mixture contain
Free ions so it will conduct electricity
What are the positive Al3+ ions attracted to
To the negative electrode is where they each pick up 3 electrons and turn into neutral aluminium atoms
What are the negative O2- ions attracted to
The positive electrode where they each lose 2 electrons
The neutral oxygen atoms will combine to from O2 molecules
Aluminium oxide —->
Aluminium + oxygen
What is reduction
A gain of electrons
What is oxidation
Loss of oxygen
A more reactive metal will …
Displace a less reactive metal from its compound
What happens if you put a reactive metal into the solution of a dissolved metal compound
The reactive metal will replace the less reactive metal in the compound
What always electrons in displacement reactions
The metal ion-so it is reduced
What is oxidised in displacement reactions
The metal atoms as they lose electrons
What is a reduction reaction
A reaction that separates a metal from its oxide
Formation of metal ore
Oxidation=
Gain of oxygen
Extraction of metal
Reduction =
Loss of oxygen
