C4 - Chemical changes Flashcards
What is an ore?
Rocks containing enough metal to be worth extracting.
What is electrolysis?
Splitting an ionic compound into simpler substances using an electric current.
When do we use electrolysis?
When our metal is more reactive than carbon. When are substance contains ions.
What is an electrolyte?
Liquid containing ions. Must be able to conduct electricity.
What is a Cathode?
Connects to the negative side of the battery (the negative electrode). Attracts cations.
What is an anode?
Connects to the positive side of the battery (the positive electrode). Attracts anions.
Why do we melt or dissolve the solution in water?
To allow ions to flow.
What does water split into?
hydrogen ions (H+) and hydroxide ions (OH-)
What are the positive ions in CuSO4 when it is dissolved in water?
Cu(charge)2+ and H+
What are the negative ions formed at the anode in CuSO4 when it is dissolved in water?
SO4 (charge)2- and OH-
What is the rule for what forms at the cathode (-)?
The less reactive positive ion forms here.
What is the rule for what forms at the anode(+)?
Oxygen forms unless a halide ion is present. (Group 7 element)
Why does CO2 form in electrolysis?
Oxygen formed from electrolysis reacts with the graphite anode, forming carbon dioxide.
When does a neutralisation reaction occur?
When an acid and an alkali react together.
What is the word equation for a neutralisation reaction?
Acid + Alkali -> Salt + Water
What do all acids contain?
H+ ions
What do all alkalis contain?
OH- ions
What determines if an acid or alkali is weak or strong?
How ionised it is in water.
Weak acid/alkali - only partially ionised in water
Strong acid/alkali - 100% or fully ionised in water.
What is oxidation?
When a substance loses electrons. (gains oxygen)
What is reduction?
When a substance gains electrons. (loses oxygen)
What is the reactivity series of metals?
Shows the metals in order of reactivity.
What groups react with water?
Mostly Group 1 metals and Group 2 metals react with water.
How are metals more reactive than carbon extracted?
Electrolysis
Why must an ionic substance have been melted or dissolved in water?
So ions are free to move.
What happens in electrolysis?
Positively charged ions move to the negative electrode. They gain electrons and are reduced.
Negatively charged ions move to the positive electrode. They lose electrons and are oxidised.
Why are carbon electrodes chosen?
Carbon electrodes are chosen because they have a high melting point and they do not react with the reactants and the products (they are inert).
What is the general equation for the reaction between metal carbonate and an acid?
Metal carbonate + acid -> salt + water + co2
What is the general equation for the reaction between metal oxides/hydroxides and an acid?
metal oxide/hydroxide + acid -> a salt + water
What do acids and alkalis produce in an aqueous solution?
Acids produce hydrogen ions. Alkalis produce hydroxide ions.
State the general equation for a neutralisation reaction in short ionic form.
H+ + OH- -> H20
How is aluminium manufactured and why is it expensive?
It is made through the electrolysis of cryolite and aluminium oxide.
It is expensive because lots of energy is needed to produce the current.
Why is cryolite used in the extraction of aluminium?
Because it lowers the melting point of aluminium oxide. Reducing energy costs.
What are the half equations in the extraction of aluminium?
Al(3+) + 3e- -> Al (cathode)
2O(2-) -> O2 + 4e- (anode)
Oxygen reacts with carbon at the anode forming C02
What is a redox reaction?
A reduction or oxidation reaction.
What is an ionic equation?
Where you only show the particles that are oxidized or reduced. e.g. Ca + Fe(2+) –> Ca(+) + Fe
What are ionic half equations?
Focuses on the ionic change of one particular element. e.g. Fe(2+) + 2e(-) –> Fe
What are the products when calcium hydroxide and hydrochloric acid react?
Calcium chloride + water
What is used to measure the unknown volume in a titration?
Burette
Why are trains powered by hydrogen fuel cells being referred to as the new steam trains?
In hydrogen fuel cells hydrogen goes to the positive electrode where it loses electrons and is, therefore, oxidized. This means it produces water.
Why must the positive electrode be continually replaced during the production of aluminium?
The carbon electrode reacts with the oxygen formed at the anode, which produces carbon dioxide. Meaning the electrode will corrode.
Why can’t sodium chloride solution be used as the electrolyte to produce sodium metal?
The less reactive metal will from at the positive electrode.
Meaning hydrogen will form instead of sodium.
Why do alkaline batteries eventually stop working?
A reactant is being used up
Why can alkaline batteries not be recharged?
The reaction is not reversible.
What is a cell?
A cell is composed of two electrodes dipped in an electrolyte solution. It creates a current from a chemical reaction.
How are metals less reactive than carbon extracted.
Reduction with carbon. Carbon displaces the metal in a metal oxide. Leaving the metal in it’s pure form.
What is the general equation for a reaction between metals and acids?
Metal + acid -> salt + hydrogen
Which metals in the reactivity series will react with an acid?
Those above hydrogen.
State a neutralisation reaction in ionic form.
H+ + OH- -> H2O
Where does reduction occur in electrolysis?
Cathode
Where does oxidation occur in electrolysis?
Anode
How is aluminium manufactured?
Electrolysis of aluminium oxide and cryolite.
Why is manufacturing aluminium expensive?
Lots of energy needed to produce the current.
What is the difference between a chemical cell and electrolysis?
Electrolysis uses electricity to produce a chemical reaction.
A chemical cell uses a chemical reaction to produce electricity.
Why is graphite used as an electrode?
Conducts electricity.
Inert (unreactive)
Why does the metal in electrolysis need to be more reactive than carbon?
So it doesn’t get displaced by carbon.
What is an alkali?
A base that dissolves in water to form a solution with a pH greater than 7.
What is a base?
Any substance with a pH greater than 7.
What are 3 common acids?
Nitric
Sulfuric
Hydrochloric
What are 3 common bases?
Metal Carbonate
Metal Hydroxide
Metal oxide
How should we evaporate the water in crystallisation and why?
Water bath/ electric heater
To avoid damaging the salt
Why is a pipette and a burette used in a titration?
Pipette used to measure fixed volume.
Burette used to measure variable volume.
Give 4 factors that affect the voltage produced by a cell.
Type of electrode.
Type of electrolyte.
Concentration of electrolyte
Temperature.
What is a cell?
A cell is composed of two electrodes dipped in an electrolyte solution. It produces current from a chemical reaction.
What is a battery?
Two or more cells connected in series.
Explain rechargeable batteries.
Chemical reactions are reversed when external current is supplied.
Explain non-rechargeable batteries.
All reactants are used up, cannot be recharged.
What is a fuel cell?
Fuel cells consist of fuel and oxygen. Where the fuel is oxidised to produce electricity.
What is a hydrogen fuel cell?
Where hydrogen is oxidised to form water.
Why should batteries not be put in household waste?
Alkaline waste can be harmful / toxic / corrosive.
What are the adv. of alkaline cells?
Cheap to manufacture.
What are the disadv. of alkaline cells?
Expensive to recycle.
Toxic waste.
May end up in landfill sites.
What is the overall equation for a hydrogen fuel cell?
Hydrogen + oxygen -> water
What is the difference between hydrogen fuel cells and electrolysis?
Electrolysis - anode is positive and cathode is negative
Hydrogen fuel cells - cathode is positive and anode is negative
What is the anode in both electrolysis and hydrogen fuel cells?
Where electrons are lost.
Difference between an alkali and a base.
Alkali is an soluble metal hydroxide, a base is a insoluble metal hydroxide or metal oxide.
What are all the charges of ions from acids?
Hydrochloric acid - Cl-
Nitric acid - NO3-
Sulfuric acid - SO42-
What happens when the concentration of H+ ions increases by a factor of 10?
pH decreases by 1 unit.
What forms from a metal + acid?
Salt + hydrogen
How can soluble salts be made?
By reacting acids with insoluble solids such as metal, metal oxide, metal hydroxide and metal carbonate.
How are metal oxides made?
Metal + oxygen
