Electrolysis Flashcards
what is not covered: Outline chemical tests that would provide evidence for the presence of H+ or OH ions in solution Give reasons why the mass lost by one electrode may not be equal to the mass gained by the other in an experimental situation
What is an ion?
charged particles that have either gained or lost electrons, making them either positively charged (cations) or negatively charged (anions)
gained a dull outer shell
Why do ionic compounds form?
Ionic compounds usually form when a metal reacts with a nonmetal, where the metallic atoms lose an electron or electrons, becoming cations (positively charged ions), and the nonmetallic atoms gain an electron or electrons, becoming anions (negatively charged ions).
What is current (chem)?
involves the movement of charged particles through a substance
why do electrons flow out of the negative terminal?
because they repel
what is needed for a substance to conduct electricity?
if it has charged particles (e.g., ions and electrons) that can move (and thus act as charge carriers)
Can copper conduct electricity?
it is a metal, therefore it has a sea of delocalised electrons which are free to move through the substance
Can a sugar cube conduct electricity?
NO-there are no free charged particles (because the sugar cube is a simple covalent substance with neutral molecules) and the particles are fixed in position
can distilled water conduct electricity?
it cant conduct electricity because the water molecules are neutral, and it doesn’t carry charged particles or delocalised electrons (to act as charge carriers)
can sodium chloride solid conduct electricity? can sodium chloride in distilled water conduct electricity?
solid - it is fixed in an ionic lattice so the charged particles can’t move
liquid - the charged particles can move and they are no longer fixed in the lattice as they are dissolved (sodium is a metal and has delocalised electrons)
can graphite conduct electricity?
graphite is a metal as it is made of carbon and has a sea of delocalised electrons which are free to move between layers and conduct electricity
what is monatomic? what type of particle is it? Which substances are in this type?
atoms which are group 0 elements
what is simple molecular? what type of particle is it? Which substances are in this type?
molecules which are mostly non-metals (except group 0), most metals made from non-metals combined
what is giant covalent? what type of particle is it? Which substances are in this type?
atoms made from diamond, silicon, graphite, silicon dioxide
what is metallic? what type of particle is it? Which substances are in this type?
ions and delocalised electrons made from metals
what are ions? what type of particle is it? Which substances are in this type?
ions made from most compounds from metals and non-metals combined
can a metal conduct electricity?
yes- it has a sea of delocalised electrons which are free to move through the structure and act as charge carriers
can an ionic solid conduct electricity?
no - electrons aren’t free to move in the lattice as they are fixed and therefore act as charge carriers
can an ionic molten or dissolved conduct electricity?
yes- there is a sea of delocalised ions which are free to move and can act as charge carriers
can graphite conduct electricity?
yes- delocalised electrons which can carry charge and move
can diamond conduct electricity?
no- there are no free electrons to carry charge which are free to move through the substance
can simple covalent conduct electricity?
no- there are no free charge carriers as the molecules are neutral
what is electrolysis?
splitting of a compound using electricity. A type of decomposition reaction (electro-electricity, lysis-splitting)
OR
the decomposition of compounds using electricity
what 3 compounds do they need for electrolysis?
electrolyte dissolved in a substance containing ions
2 electrodes (e.g., graphite, platinum, a metal)
power source
what is a cation and an anion? Which go to the anode and cathode
a positive ion and a negative ion. the cation goes to the cathode (negative electrode) and vice versa
what is the half equation for metals? and non metals?
metals (atoms to ions) - M -> M+ + e- (and vice versa)
non metals (molecules to ions) X2 + 2e- _> 2X-
be able to label/draw a diagram of molten electrolysis?
things that must be there:
anode
cathode
heat
anions going to the anode which is positively charged
cations going to the cathode which is negatively charged in order to attract the cations
the battery (one big line (positive- leading to anode), one shorter one (negative) leading to the cathode)
the movement of electrons on the wire
the metal becoming neutral at tthe bottom and if a gas is produced two circles which are smucshed together and half in an out of the liquid
e.g., lead bromide - lead going to the cathode, bromide going to the anode, bromine gas being produced, molten lead being produced
what happened at the anode? (and cathode)
anode- negative ions lose electrons and become neutral
OXIDATION
cathode- positive ions gain electrons and are reduced
how can you collect gas from the anode
with a glass tube
how can lead be collected from molten electrolysis
lead is heavier and can be collected it decanted
why do graphite electrodes need to be replaced?
they need to be replaced every 28 days because after a while the carbon begins to react
what is an ore?
a rock containing enough of a metal in its compound form for it to be profitable to extract (that metal)
what is the metal reactivity series?
Potassium
Sodium
Lithium
Calcium
Aluminium
(metals above can be extracted by electrolysis due to their high reactivity)
Carbon
Zinc
Iron
Lead
(hydrogen)
copper
(metals below carbon are exracted by heatin them with carbon in a blast furnace)
silver
gold
platinum
(their low reactivity means that they will be found on their own as they are so unreactive and they are often found on their own - native)
why is electrolysis so expensive?
- heating the compound
- energy (flow of electrons)
what is so special about water?
although water is a covalent molecule, a small fraction of water molecules are always ionised in a reversable reaction.
equilibrium lies far to the left (most of it is water) but there will always be few ions [present in any sampple of water
what happens at the anode during electrolysis in the solution?
- if halide ions (group 7) are present then the halogen id produced (e.g., CL2)
- otherwise (if not e.g., NO3-, CO32-, SO42- present) then oxygen (O2) gas will be produced from hydroxide ions (OH-)
what happens at the cathode during electrolysis in the solution?
the least reactive element at the CATHODE
what is the half equation of hydroxide?
4OH- -> O2 + 2H2O + 4e-
what is they half equation for H=?
2H+ 2e- -> H2
when can ions conduct electricity?
ions can only conduct if the ions are mobile in a solution or liquid
what is oxidation? reduction?
oxidation - if it loses an electron
reduction- if it gains an electron
Explain how carbon could be used to extract a metal
carbon can be used to extract a metal below it in the reactivity series from its ore in a displacement reaction in a blast furnace and it is very cheap
what metals are extracted using electrolysis?
elements above carbon
What is the chemical test for hydrogen?
use a lit splint in an upturned test tube and it will give off a squeeky pop
What is the chemical test for oxygen?
oxygen is present if it relights a glowing splint (in a test tube)
What is the chemical test for chlorine?
use damp blue litmus paper and it will bleach. It needs to be damp so the chlorine dissolves
(in some demonstrations from electrolysis this wont work because e.g., the sodium chloride electrolysis and the gas cant escape)
How can electrolysis be used to create a thin layer of metal on the electrodes
electrolysis can be used to create a thin layer of a metal on a conductive object (electroplating) .
e.g., a solution creating gold ions is attracted to the anode (e.g., sterling silver jewelry) and gold is deposited on the layer of the anode. You could ensure this happens by measuring mass or colour change
what can be produced from electrolysis of sodium chloride?
electrolysis of sodium chloride solution can be used to produce hydrogen, chlorine and sodium hydroxide
draw a diagram of electrolysis in a solution of sodium chloride
a negative and positive electrode
hydrogen going to the cathode/negative electrode
chlorine going to the anode/positive electrode
sodium and hydroxide being left over
how to know in a question if it is molten electrolysis or in a solution?
molten - liquid
in a solution - aqueous
how can magnesium be used to separate a metal?
using displacement
does ammonia conduct electricity?
yes
what does the acronym PANiC stand for?
positive anode, negative (is) cathode)
what is an electrolyte?
a liquid or solution that undergoes electrolysis
All electrolytes contain ions
why is carbon used frequently as an electrode
because it is inert (not very reactive)
what happens at the electrode to an ion
it is discharged (loses its charge)
what does the acronym OILRIG stand for?
Oxygen Is Loss of electrons Reduction Is Gain of electrons
why cant some ionic compounds be electrolysed?
some break up into simpler substances before their melting point e.g., copper (II) carbonate breaks into copper (II) oxide and carbon dioxide
Explain the electrolysis of copper (II) sulfate solution using inert electrodes and the mass changes including when copper is used at the positive electrode
Copper and hydrogen will be attracted to hydrogen. Copper is below hydrogen in the reactivity series so it will more easily add electrons to form an atom (cathode is then coated in pink-brown copper)
Sulfate and hydroxide ions are attracted to the anode and the sulfate ions aren’t easy to oxidise so you get oxygen
If electrolysis continues for a long time the copper ions will eventually fade from blue to colourless
Hydrogen and sulfate ions not used so the solution turns into sulfuric acid and the electrolysis will continue for dilute sulfuric acid (?)
Therefore the mass increases at the positive electrode.
Inert electrodes are used because sometimes it can affect the product you get e.g., if copper electrodes were used, oxygen gas is not produced, rather the anode gets smaller
why do you use distilled water in electrolysis of solutions
There are no other ions or minerals in distilled water to affect electrolysis
What is the test for H+ ions
OH- ions in a solution
Acids contain H+ ions, and bases contain OH- ions, so you can use a few drops of universal indicator. If H+ - would go red/ orange, if OH- would go purple/blue
