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
What is a salt?
An ionic compound formed during the reaction between an acid and a base
List the 4 outcomes:
Acid + Metal -> Salt + Hydrogen
Acid + Alkali -> Salt + Water
Acid + Base -> Salt + Water
Acid + Metal carbonate -> Salt + Water + Carbon dioxide
What happens when a metal reacts with oxygen?
A metal oxide is formed
What happens when a metal reacts with water?
Metal hydroxide and hydrogen is formed
What happens when a metal reacts with dilute acid?
Metal + acid -> Metal salt + hydrogen
Keep in mind that only metals more reactive than hydrogen do this
What is a displacement reaction?
A reaction where a more reactive element takes the place of a less reactive element in a compound
What happens when metals react?
They lose electrons to form positive ions. The greater the tendency of a metal to do this, the more reactive it is
What is a redox reaction?
A reaction in which both reduction and oxidation take place
What is titration?
A titration is used to measure the volume of one solution that exactly reacts with another solution
How would you prepare a pure dry sample of salt from an oxide or carbonate?
Place 25cm^3 of dilute sulfuric acid in a conical flask
Warm the acid with a bunsen burner
Add magnesium carbonate and stir until it’s in excess
Filter the solution with filter paper
Heat the filtered solution to make it more concentrated
When you cool it, salt crystals will form, which you can then filter out and dry
How would you carry out a titration?
Measure out a known volume of a solution of an acid with a pipette and place it into a conical flask
Add a few drops of indicator
Add drops of the other solution from the burette until the indicator changes colour
Record the volume added from the burette
Repeat the experiment until you get concordant results
