Chapter 4: Chemical changes Flashcards
What is electrolysis?
The process of breaking down ionic substances by passing an electric current through them. For example, it can be used to separate metals from their ores.
What is an electrolyte?
A liquid that conducts electricity
What is the anode?
The positive electrode, where oxidation (the loss of electrons) takes place
What is the cathode?
The negative electrode, where reduction (the gain of electrons) takes place
Why can’t ionic compounds conduct electricity as solids?
Because the ions can’t move around, unlike when the compound is melted or dissolved
How does electrolysis work?
The 2 electrodes are placed into the electrolyte and connected to a power supply. Since opposite charges attract, the negative ions are attracted to the positive electrode and vice versa. At the electrodes, the ions are discharged and become neutral, while the electrons move through the wires and back to the other electrode.
What do you need to remember when writing half equations?
The non-metals at the positive electrode often come in pairs of 2
Why can some metals only be extracted from their ores using electrolysis?
Their oxides can not be reduced by heating with carbon because they would either react with the carbon or are already more reactive than carbon
Why is electrolysis expensive?
Because of the high cost of the electricity and heat energy required to melt the metals
Why do electrodes sometimes have to be replaced?
Because the products sometimes react with the electrode itself
What are inert electrodes?
Electrodes that allow electrolysis to take place but do not react themselves
How is electrolysis different when the ionic compound is dissolved in water?
A small fraction of the molecules in the water break down into hydroxide and hydrogen ions, which are discharged at the electrodes and
What are ionic equations?
Equations where the spectator ions (ones that don’t change) are removed. For example: HCl + NaOH -> NaCl + H2O would become H+ + OH- -> H2O
How do you prepare a salt from an insoluble base and an acid?
Warm up the base,
What is the difference between a base and an alkali?
An alkali can dissolve in water, while bases (e.g. sodium hydroxides, metal oxides) cannot
