Chemical Changes Flashcards
What does the pH scale go from?
0 to 14
True or false : The lower the pH of a solution, the more alkaline it is.
False - the lower the pH, the more acidic
What is the pH of a neutral substance?
7
How can you measure the pH of a solution?
An indicator (dye that changes colour)
A pH probe attached to a pH meter
What do acids and bases do to each other?
neutralise each other
What is an acid?
A substance that forms an aqueous solution with a pH of less than 7.
What ions do acids form in water?
H+ ions
What is a base?
Any substance that will react with an acid to form a salt.
What is an alkaline?
A base that dissolves in water to form a solution with a pH greater than 7.
What ions do alkalis form in water?
OH-
What is the word equation for neutralisation?
acid + base —> salt + water
What is the ionic equation for neutralisation?
H+ + OH- —> H2O
What are titrations used for?
To find out exactly what volume of acid is needed to neutralise a measured volume of alkali - or vice versa.
How would you measure the alkali?
Using a pipette and pipette filler
What do you add to the alkali?
An indicator
Give two examples of indicators in titrations.
Phenolphthalein and methyl orange
What colour is phenophthalein in acids?
Colourless
What colour is phenolphthalein in alkalis?
pink
What colour does methyl orange in an acid turn when an alkali is added?
From red to yellow
What is the acid stored in, in a titration?
A burette with an unknown concentration
Give the method for titrations. RP
- Use a pipette and pipette filler to add a set volume of alkali to a conical flask. Add two drops of indicator.
- Use a funnel to fill a burette with an unknown concentration of acid. Record the initial volume.
- Use the burette to add the acid a bit at a time, whilst swirling the conical flask. Go slowly when you think the endpoint is about to be reached.
- When the indicator has changed colour, the alkali has been neutralised.
- Record the final volume of thr acid in the burette and use it to calculate the volume used to neutralise the alkali.
Name the 4 apparatus used in titrations.
Pipette, Burette, Scale, Conical flask
What could you do to calculate a mean volume of acid in titrations?
Repeat
What do acids produce in water?
protons or H+ ions
What do acids do in aqueous solutions?
ionise, they produce H+ ions
What is meant by a strong acid?
They ionise completely in water, all particles dissociate to release H+ ions.
What is meant by a weak acid?
They do not fully ionise in a solution, only a small proportion of particles dissociate to release H+ ions.
What type of reaction is the ionisation of a weak acid?
reversible reaction
What is meant by the pH of an acid or alkali?
The concentration of H+ ions.
Complete the sentence: For every decrease of 1 on the pH scale, the concentration of H+ ions ___________ by a factor of ___.
increases, 10
What is meant by a concentrated acid?
A large amount of acid in a certain volume of liquid.
What is meant by a dilute acid?
A small amount of acid in a certain volume of liquid.
What are metal oxides and metal hydroxides?
Bases
What does an acid + a metal oxide/hydroxide produce?
Salt + Water
What does an acid + a metal carbonate produce?
Salt + Water + Carbon dioxide
How can you make soluble salts using an insoluble base? RP
- Gently warm the acid using a bunsen burner then remove from the heat.
- Add the insoluble base in excess to the acid.
- Filter out the excess solid to get the salt solution.
- Gently heat the solution in an evaporating basin over a bunsen burner until about half has evaporated and crystals have begun to form.
- Stop heating and leave the solution to cool or pat dry.
List the reactivity series?
Potassium
Sodium
Lithium
Calcium
Magnesium
Aluminuim
Carbon
Zinc
Iron
Tin
Lead
Hydrogen
Copper
Silver
Gold
What is the most reactive element in the reactivity series?
Potassium
What is meant by reactivity?
How easily an element loses electrons
What does an acid + metal produce?
Salt + hydrogen
What does a metal + water produce?
Metal hydroxide + hydrogen
What metals don’t react with water?
zinc, iron, copper
What are ores?
Compounds that contain an element due to its reactivity.
What is oxidation?
The gain of oxygen
What is reduction?
The loss of oxygen
What is an oxide?
A metal compound that contains oxygen
How can metals be extracted by reduction?
Using carbon
What metals can be extracted by carbon?
Metals below carbon in the reactivity series
What does OILRIG stand for?
Oxidation
Is
Loss (of electrons)
Reduction
Is
Gain (of electrons)
What is a redox reaction?
When reduction and oxidation happen at the same time.
What are three examples of redox reactions?
Metals reacting with acids
Halogen displacement reactions
Metal displacement reactions
What happens when metals react with acids?
Metal atoms become oxidised (lose electrons)
The hydrogen ions are reduced (gain electrons)
Complete the sentence: A ________ reactive halogen can displace a ________ reactive halogen from a salt solution.
More, less
Which ion becomes reduced when copper sulphate is reacted with iron?
Copper gains electrons
What is meant by electrolysis?
Splitting up with electricity
During electrolysis, what is passed through the electrolyte?
An electric current.
What is an electrolyte?
A molten or dissolved ionic compound
What charge does the cathode have?
Negative
What charged ions does the cathode attract?
Positive
What happens to the ions at the cathode?
They become reduced/gain electrons
What is the positive electrode called?
The anode
What charged ions does the anode attract?
negative
What happens to the ions at the anode?
They become oxidised/lose electrons
What does electrolysis of molten ionic solids form?
elements
Why can’t ionic solids be electrolysed?
The ions are in fixed positions and can’t move
In electrolysis of molten ionic solids, what type of ion is reduced at the cathode?
metal ions
In electrolysis of molten ionic solids, what type of ion is oxidised at the anode?
non-metal ions
What are electrodes made of?
An inert material, often graphite
What metals are extracted by electrolysis?
Metals more reactive than carbon
What are the disadvantages of electrolysis?
Very expensive and requires lots of energy
What ore is aluminium extracted from?
bauxite
What does bauxite contain?
Aluminium oxide
True or false : Aluminium oxide has a low melting point.
False - it has a very high melting point
What is aluminium oxide mixed with to lower its melting point?
cryolite
In electrolysis of aluminium oxide, what ions are attracted to the negative electrode?
Positive Al3+ ions are attracted to the cathode where it gains electrons to produce aluminium atoms.
In electrolysis of aluminium oxide, what ions are attracted to the positive electrode?
Negative O2- ions are attracted to the anode where they lose two electrons. They then combine to form O2 molecules.
What happens at the negative electrode during electrolysis of molten ionic solides?
Metals form positive ions. The metal is produced
What happens at the positive electrode during electrolysis of molten ionic solides?
Non-metals form negative ions.
Oxygen is produced
What happens at the cathode during the electrolysis of aqueous solutions?
If the metal is less reactive tham hydrogen, the metal is produced.
If the metal is more reactive than hydrogen, hydrogen is produced.
What happens at the anode during the electrolysis of aqueous solutions?
If no halide ions are present, oxygen and water is produced.
If halide ions are present then molecules of the halogen is produced.
What is formed at the cathode and anode in the electrolysis of copper sulfate solution?
Cathode: Copper
Anode: Oxygen
What is formed at the cathode and anode in the electrolysis of sodium chloride solution?
Cathode: Hydrogen
Anode: Chlorine
What are half equations?
Equations that show the reactions at the electrodes
If no halide ions are present, give the half equation for the anode.
4OH- — 4e- —> O2 + 2H2O
What is the half equation at the cathode if the metal is more reactive than hydrogen?
2H+ + 2e- —> H2
