Topic 3 - Chemical Changes Flashcards
What do acids form in water?
H+ ions
What does the higher the conc of H+ mean?
The more acidic the solution is
What do alkalis form in water?
OH- ions
What does the higher the conc of OH- mean?
The more alkaline the solution is
What is a base?
A substance which reacts with an acid to produce a salt and water
What is an indicator?
A dye that changes colour depending on whether it’s above or below a certain pH
State the colour of litmus in acid?
Red
State the colour of litmus in neutral?
Purple
State the colour of litmus in alkaline?
Purple
State the colour of methyl orange in acid?
Red
State the colour of methyl orange in neutral?
Yellow
State the colour of methyl orange in alkaline?
Yellow
State the colour of phenolphthalein in acid
Colourless
State the colour of phenolphthalein in neutral?
Colourless
State the colour of phenolphthalein in alkaline?
Pink
What does neutralisation produce?
Salt and water
State the neutralisation ionic equation?
H+ + OH- -> H2O
The pH of an unknown solution is 2
Is the solution acidic or alkaline?
Acidic
How do you investigate the neutralisation reaction of CaO and HCl?
Measure out HCl and CaO
Add and then record pH and repeat
What does dissociating H+ mean?
Splitting up to produce hydrogen ions
What are strong acids?
Acids that almost completely ionise in water
What are weak acids?
Acids that partially ionise in solution
What type of reaction is the ionisation of a weak acid?
A reversible one
What are alkalis?
Soluble bases
What does acid strength tell you?
What proportion of the acid molecules ionise in water
What does acid strength tell you?
What proportion of the acid molecules ionise in water
What does acid concentration tell you?
How much acid there is in a volume of water (how watered down the acid is)
Describe a dilute acid?
An acid with a small number of acid molecules compared to the volume of water
Describe a concentrated acid?
An acid with a large number of acid molecules compared to the volume of water
What does acid concentration not describe?
The number of molecules that produce hydrogen ions
How does a decrease in 1 pH affect a solutions H+ ions level?
1 less pH will mean 10x more H+ ions
A solution with a hydrogen ion concentration of 0.001 M has a ph of 3
What would happen to the pH if you increased the hydrogen ion concentration to 0.01 M
The H+ concentration has increased by 10x therefore the pH would decrease by 1
3 - 1 = 2
Explain the difference between a strong acid and a weak acid?
A strong acid ionises almost completely in water whilst a weak acid only partially ionises in water
A student added a strong acid to a solution with a pH of 6
The new solution had a pH of 3
State whether the concentration of H+ had increased or decreased and by what factor
Increased by x10^3
Acid + Metal Oxide =?
Salt + Water
Acid + Metal Hydroxide =?
Salt + Water
Acid + Metal =?
Salt + Hydrogen
Acid + Metal Carbonate =?
Salt + Water + Carbon Dioxide
How can you test for hydrogen?
A lit splint making a ‘squeaky pop’
Where does the pop in the ‘squeaky pop’ test come from?
The hydrogen burning with the oxygen in the air
How do you test for carbon dioxide?
Bubble the gas through lime water and if the water goes cloudy, Carbon dioxide is present
Write a symbol equation for the reaction of hydrochloric acid with calcium carbonate?
HCl + CaCO3 -> CaCl2 + H20 + CO2
Write a balanced symbol equation for the reaction of hydrochloric acid with calcium carbonate?
HCl + CaCO3 -> CaCl2 + H20 + CO2
2HCl + CaCO3 -> CaCl2 + H20 + CO2
What salt’s are always soluble?
Sodium, potassium, ammonium and nitrates
What chlorides are insoluble?
Silver and lead
What sulfates are insoluble?
Lead, Barium and Calcium
What carbonates/hydroxides are soluble?
Sodium, Potassium and Ammonium
What do you need to pick when making salts via precipitation?
Two soluble salts that react together to form an insoluble salt
Explain why, if soluble salts are prepared from an acid and an
insoluble reactant an excess of the reactant is added?
To ensure all of the acid has reacted allowing the solution to be made of the products and the insoluble excess reactant which can easily be filtered
Suggest two reactants you could use to form barium sulfate in a precipitation reaction?
Barium Nitrate + Sodium Sulfate
When given a insoluble salt and asked for two soluble salts that could be used, whats a easy way to answer without having to ensure they are soluble
_____ Nitrate + Sodium _____
When reacting acid with a base, why is it heated?
To speed up the reaction
When adding base to acid, when can you tell all the base has been used?
The base no longer reacts with the acid, instead it sits at the bottom of the flask
How do you neutralise an acid with an alkali?
Titration
How do you do titration?
You do a rough titration and add acid into a flask and indicator, then add alkali until the end point is reached
Then repeat, without indicator, at much slower incriments and then slowly evapourate off some of the water and then leave the solution to crystallise
Iron Nitrate is a soluble salt that can be made from iron oxide and nitric acid
Suggest which method you should use?
Excess base
What two things does elecrolysis involve?
Reduction and oxidation
What are electrolytes?
Molten or aqeous ionic compounds
What type of current must electrolysis have?
Direct Current
Describe electrolysis
A process where electrical energy, from DC, decomposes electrolytes
What ions migrate to the cathode?
Positively charged cations
What ions migrate to the anode?
Negatively charged anions
What charge is the cathode?
Negative
What charge is the anode?
Positive
Where would Mg2+ go to in electrolysis?
The cathode
Where would Cl- go to in electrolysis?
Anode
What ions are oxidised in electrolysis?
Anions
What ions are reduced in electrolysis?
Cations
What happens to the cations in electrolysis?
They go to the cathode and reduce
What happens to the anions in electrolysis?
They go to the anode and oxidise
Give eamples of inert electrodes?
Graphite and platinum electrodes
What is formed in copper chloride molten?
Copper at cathode
Chlorine gas at anode
What is formed in sodium chloride molten?
Sodium at cathode
Chlorine gas at anode
How do you electrolyse a molten ionic substance?
Put the solid substance in a crucible and melt it
Dip two electrodes into the liquid and then connect the electrodes to a power supply
At which electrode does oxidation happen?
Anode
How do you electrolyse a solution?
Clean electrodes with emery paper
Add electrodes into solution
And turn on the circuit
Why can’t an ionic solid be electrolysed?
Because the ions are in fixed positions and can’t move
How is what appears at the cathode get decided in a solution?
Based on whether the metal is more reactive than the hydrogen
If a metal is more reactive than hydrogen, what will appear at the cathode?
The hydrogen
If a metal is less reactive than hydrogen, what will appear at the cathode?
The metal
How do you remember what appears at the anode?
If its an ate, It “ate”‘n’t that one
If its an ide, “Ide” bet it’s that one
If its an halide, “Ide” bet on “hal” it’s that one
When a solution of sodium chloride is electrolysed where and what is formed?
Hydrogen at cathode
Chlorine gas at annode
When a solution of sodium sulfate is electrolysed where and what is formed?
Hydrogen at cathode
Oxygen at cathode
When a solution of sulfuric acid (H2SO4) is electrolysed where and what is formed?
Hydrogen at cathode
Oxygen at anode
What is the half equation at an anode when oxygen is produced?
4OH- -> O2 + 2H2O + 4e-
An aqueous solution of copper bromide, CuBr2, is electrolysed using inert electrodes
Give the half equation to show the reaction occurring at the anode
2Br- - e- -> Br2
What four different ions does copper sulfate (aq) contain?
Cu2+, H+, OH- and SO4(2-)
What do you get when you electrolyse copper sulfate solution with inert electrodes?
Copper at the cathode
Oxygen at the anode
What do gases appear as in electrolysis?
Bubbles
What happens when you electrolyse copper sulfate with copper electrodes?
The mass of the anode will decrease whilst the mass of the cathode will increase
Why does the mass of the anode will decrease whilst the mass of the cathode will increase when electrolysing copper sulfate with copper electrodes?
The copper from the anode is being transferred to the cathode
What should you ensure before weighing electrodes?
The electrodes are dry
Why must the electrodes be dry when weighing?
To increase the accuracy of the results
What happens to the rate of electrolysis as you increase current?
It increases
How does the electrical supply work in the electrolysis of copper sulfate with copper cathodes?
Pulls electrons off the copper anode
Offers electrons at the cathode to nearby copper ions
What happens to the impure copper annode during electrolysis?
It is oxidised and dissolves into the electrolyte to form copper ions
What happens to the copper ions during electrolysis?
They are reduced at the cathode and add to it as a layer of pure copper
What happens to the impurities from the impure copper anode during electrolysis?
They sink to the bottom forming a sludge
Explain how electrolysis is used to purify copper for use in electrical circuits?
The anode is a large thick pick of impure copper whilst the cathode is a thin piece of pure copper. During the electrolysis the supply pulls electrons off the atoms so they dissolve and form copper ions. The copper ions migrate to the cathode where the yaccept electrons to reform copper atoms and coat the cathode with a pure layer of copper
State what colours; litmus, methyl orange and phenolpthalein will turn in acidic solutions?
Litmus - Red
Methyl Orange - Red
Phenolpthalein - Colourless
What does a pH curve look like?
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---------/Write an equation to show how ethanoic acid acts as a weak acid?
CH3COOH ⇌ CH3COO- + H+
If you increase the hydrogen ion conc of a solution by a factor of 10, what will happen to the pH of the solution?
Decrease by 1
Write a chemical equation to show how HCl reacts with CuO?
2HCl + CuO -> CuCl2 + H2O
Describe a test you could carry out to test for hydrogen gas?
A lighted splint making a squeaky pop
What would you expect to see if you bubbled carbon dioxide through limewater?
It will turn cloudy
List three insoluble sulfates
Lead, barium and calcium
Name two soluble hydroxides?
Potassium and sodium
Towards which electrode do the anions move?
The anode
Why do the masses of non-inert electrodes change during electrolysis?
The non-inert anode loses its mass to the non-inert cathode
