topic 4 Flashcards
how do we measure ph
indicators-(chemical dyes)
ph probe connected to ph meter
what is an acid
any substance that forms an aqeous solution with ph less than 7 which is made acidic from the h+ ions they release in water
what are bases
any substance of ph greater than 7
what are alkalis
a sub group of bases that are soluble in water- a base that dissolves in water to form a solution with a ph greater than 7
what is an acid +base reaction called and what does it produce
a neutralisation reaction
- produces water and salt
-baws
what is the formula for sulfuric and nitric acid
-h2so4
-hn03
what are formulas for calcium carbonate /sodium hydroxide
NaOH/CaC03
what is a titration
an experimental technique to find an unknown conc of an acid or alkali
list equipment needed for titration
-a pipette to measure 25cm3 volume of acid or alkali
-conical flask to hold the liquid from the pipette
-a burette to add acid or alkali
-white tile to place conical flask
titration method
1) use pipette to add 25cm3 of alkali to conical flask
2)add few drops of indicator and put the conical flask to the white tile
3)fill the burette with acid and note the starting volume by reading it off the burette
4)Add acid from the burette to alkali in conical flask swirling it to mix
5)Stop adding acid when all acid has neutralised alkali and the indicator changes colour
6)Read volume of acid remaining in burette and calculate the volume of acid added
7)Repeat the titration until you get concordant(0.10 cm3 of each other)
8)Find the mean volume of acid required to neutralise the alkali using concordant results
list the indicators and how they would be used
-litmus-red in acidic and blue in alkaline
-phenolphthalein-colourless in acidic and pink in alkaline
-methyl orange-red in acidic solutions and yellow in alkaline solutions
list some safety precautions
wearing gloves to reduce risk of harm from acid burns
what does the term ionise mean
for particles to split or dissasociate to release ions
what are some strong acids vs weak acids
strong include sulfuric acid /hydrochloric/nitric
weak acids include ethanoic/citric/carbonic
why are weak acids not completely ionising
its ionisation is reversible so there is an equilibrium between the undissociated and dissociated forms of the acid
therefore the equilibrium will lie to the left are there are far more undissociated forms of the acid
what is an acids strength or weakness
how much an acid dissasociates
what is the relationship between ph and hydrogen ions
the lower ph higher conc of h+ ions
at any concentration what do strong acids have over weak acids
At low ph a higher proportion of h+ ions will dissasociate
Moaws
what do metal oxides/hydroxide + acid form
salt +water
how do we form salts with words
take the -ion from acid and combine w +ion from base
cawcs
metal carbonate +acid
=h20 +co2 and salt
how do we make soluble salts
from an acid + insoluble base
1)put dilute acid(eg hcl in a beaker)
2)gently heat with a bunsen burner
3)add insoluble base(eg copper oxide) a little a time
-it will keep dissapearing but at some point base no longer dissapears so we know base must be in excess so we have neutralised the acid
4)filter out excess base using filter paper and funnel
5)what we have is the dissolved form of soluble salt(copper chloride)
6)gently heat up solution using water bath to evaporate some water off
7)Stop heating it and let it cool
8)Filter crystals out with filter paper and funnel
9)leave it somewhere warm or dab with filter paper
what is the reactivity series
potassium
sodium
lithium
calcium
magnesium
CARBON
zinc
iron
HYDROGEN
copper
what is metal +acid
salt +hydrogen gas
how do we get the reactivity series
by reacting the metals with acid and water to see how violent the reactions are
how does pottasiums reaction with acid differ with copper or magnesium
potassium reacts explosively catching fire and whizzing around and producing alot of hydrogen
-magnesium produces a lot of bubbles
-copper doesnt react at all
what is another way we can see how reactive a metal is
we can measure the temp change as the most reactive metals produce the most heat
-we must make it a fair test by
-using metals of same mass and sa
-same type and conc of acid each time
metals + water
metal hydroxide+hydrogen
however only most reactive metals can do this
mg only reacts slightly
what is oxidation and reduction
oxidation-gain of oxygen
reduction-loss of oxygen
what is an exception to metals reacting with oxygen
unreactive metals that havent been oxidised which are found as pure metals
how can we reduce metal oxides to get pure metals and what are the limits to this
react it with carbon to form carbon dioxide and leave behind a pure metal
we can only do this to metals less reactive than carbon
zinc
iron
copper
what are ores
metal rich compounds from rocks in the ground that we can extract our metal from
what is the most common ore
fe2o3
Why do we find pure gold in the ground, but not pure iron?
Gold is unreactive, so doesn’t react with any other elements
Iron is reactive enough to react with oxygen so is oxidised to iron oxide
what is a redox reaction
when oxidation and reduction both occur at the same time
what is oilrig in terms of electrons
oxidation is loss
reduction is gain
where are some places we see redox reactions
in displacement reactions where spectator ions are removed if they dont change at all from reactants to products)
how do you write half equations and what is the scenario you need to write them in
get the reactant element and if it has no charge write an arrow.get the product of the same element and add the electrons it has gained in the form of (e-)
get the reactant element and if it has charge add the number of electrons it will take to become what
it is as a product
This will be after you have cancelled out the spectator ions and have ypur ionic equation
what is the half equation for the reduction of oxygen
o2 +4e->2o2-
in displacement reactions what happens to the metal ions
they are reduced
in electrolysis what side will the shorter lines of the cells be
on the cathode side
what equipment is used in electrolysis
beaker
electrolyte
what is an electrolyte
liquid or solution that contains an ionic compound with ions free to move
what can we do if our compound is soluble or insoluble
dissolve it in water or melt it to make ions free to move
what are electrodes
solid conductors generally made of metal or carbon
what are the left and right electrode
cathode on the left is negative
anode on the right is positive
after we have a beaker / electrolyte and electrodes what else do we need
-power supply like a battery
-wire so electrons can flow in between the cathode and anode
what is the meaning of electrolysis
splitting up with electricity
how does electrolysis split these compounds
by using battery to pass current through electrolyte we can seperate our compound
as - ions are attracted to anode and are discharged(turned from charged ions to neutral atom)
if this was bromine atoms would pair up and form bromine gas which would float off
lead would sink to the bottom forming layer of molten lead
what happens ions at the electrodes
they are reduced and oxidised
describe the journey of electrons in electrolysis
electrons from the bromide ions at the anode travel through the wires with the battery transported along the wire to the cathode using the power of the battery
what is the half equation rule for electrolysis
the - ion is oxidised which forms the pure element+the electrons it loses
eg:at the anode - bromide ions loses electrons
2br->br2+2e-
at the cathode-lead ions gains electrons so reduced into pure lead
pb2+ +2e->pb
how does electrolysis convert ions in a compounds into their pure elemental forms
using electricity by transferring electron from negative ions to positive ions
in electrolysis, why does the compound you’re trying to separate need to be molten or dissolved
So that the ions are free to move around (and go to their respective electrode)
what is bauxite
the ore of aluminium oxide
what is the step of obtaining aluminium from bauxite
1)purify aluminium oxide from bauxite we mine from ground
2)melt aluminium oxide to make it molten(has a melting point of over 2000 degrees)
3)mix cryolite mineral with aluminium oxide which lowers melting point
4)melt it and now we have our molten aluminium oxide
what are the steps for the electrolysis of aluminium oxide
1)o2- ions will go to anode and be oxidised losing 2 electrons and be discharged to neutral oxygen atoms where 2 will combine to form an oxygen molecule and float off into the air
2)The electrons of the oxygen ion will travel through the anode and the wire and reach the cathode on the left attracting the positive aluminium ions.it will donate 3 electrons to each al3+ ion to form aluminium atoms which will then fall to the bottom of the beaker as molten aluminium metal.
what are the half equations for the cathode and the anode in the electrolysis of molten aluminium oxide
anode- 2o2->o2+4e-
cathode- al3+ +3e->al
what is the overall equation for electrolysis of aluminium oxide
2al2o3 (l) > 4al (l) +3o2 (g)
Why is electrolysis not used to extract all metals?
Electrolysis is expensive because it requires a large amount of electricity
what are soluble compounds that can be dissolved in water to serve as the electrolyte
copper sulfate -cuso4
sodium chloride- nacl
why is it difficult to work out which ions would go to each electrode in aq solution
there would also be hydroxide ions and hydrogen ions from the water in solution as it splits up when in solution
what are rules for electrolysis in aq solutions at the cathode
positive ions go to cathode including ion from compound and h+ and the least reactive is the one that will be discharged
eg: if it was copper hydrogen copper would be discharged
at the anode if a halide is present it will get discharged but if it isnt the hydroxide will always get discharged
what happens in electrolysis of copper sulphate
copper is formed at the cathode and accumulates around the cathode as it is solid
at the anode hydroxide is formed so give up extra electron to anode and form oxygen and water
the equation is
4oh->2h2o +o2 +4e-
what happens in the aq electrolysis of nacl
na is formed at the cathode
chloride is formed at the anode
why does the ph of acids depend on strength and conc of acid
General principle
* pH depends on H+ ion concentration
* the higher the concentration of H+ ions the lower the pH
Strength
* the stronger an acid the greater the ionisation / dissociation (in
aqueous solution)
* (so) the stronger the acid the lower the pH
Concentration
* the higher the concentration of an acid the more acid / solute in
the same volume (of solution)
* (so) the higher the concentration of the acid the lower the pH
temp change prac for neutralisation reactions
1)put 25cm3 of 0.25mol/dm3 hcl and sodium hydroxide
2)place beakers in water bath of 25 degrees until they reach it
3)add hcl followed by naoh to polystyrene cup with lid with thermometer and place this beaker in a large beaker with cotton wool
4)take temp every 30s
5)repeat using 0.5 mol/dm3 then 1mol/dm3 hcl
