chemical changes CGP Flashcards
what is an acid
what ions do acids form
what are bases
a substance that forms an aqueous solution with ph less than 7
form H+ ions in an aqueous solution
ANY substance that reacts with an acid to form a salt
what are alkalis
what ions do they form
a base that dissolves in water to form a solution with ph above 7
Form OH- ions in water
What is an indicator
What are wide range indicators- what are they useful for
How is ph probe used
Why is a probe better than indicator
-indicator- a dye that changes colour depending on PH
-indicators w/ mixture of dyes, gradually change colour (over broad range of ph) useful for estimating ph
-ph probe-attached to ph meter. PH given as numerical value.
-more accurate as it gives numerical value
what is the neutralisation reaction:
worded-
in terms of ions-
what is the ph of the products
how can you show neutralisation is over
acid + base = salt + water
H+(aq) + OH-(aq) = H¬2O (l)
Ph 7
use an indicator
how to carry out titration RP
if you want to find out concentration of an alkali
6 steps
-use pipette + pipette filler, add set volume of alkali to conical flask
-add 2/3 drops indicator
-use funnel- fill burette w/ acid of KNOWN concentration- do below eye level( dont want acid from burette to fall into eye) Record initial vol of acid in burette
-use tap on burette to add acid , constantly swirl conical flask, go slower when near end point(colour change)
-permanent colour change when all alkali is neutralised
-use burette to find volume of acid used to neutralise alkali
what do titrations help you work out
2 things-
-Volume of an acid needed to neutralise an alkali or VICEVERSA
this helps work out:
-Concentration of the acid/ alkali
-safety precaution in RP titrations
-what type of indicator should be used
wear safety goggles, eg bcse acid could spill into eye
-a single indicator- not wide range-need a sudden colour change at end point
RP titration
why should you repeat the your titration
what is the point of the first titration
when you repeat the titration, how do you know your getting a similiar answer
what would you do to an anomolus result
-to increase accuracy and spot anomalous results
-first one = rough titration- gives approximate of where end point is reached
-answers should be within 0.1 cm cubed of eachother
-ignore anomalous result and calculate mean.
define strong acid and explain
define weak acid and explain
strong acids - completely ionise in aqueous solutions- all the acid particles dissociate(split) into their ions, so all the acid particles release H+ ions
weak acids- partially ionise in aqueous solutions, small % of acid particles dissociate (split) into their ions and release H+ ions
examples of strong acids x3
hydrochloric acid
nitric acid
sulfuric acid
examples of weak acids x 3
ethanoic acids
citric acids
carbonic acids
*ionisation of weak acids is a …… reaction
-where does equilibrium lie in ionisation of weak acids
-why is this
reversible
-to the left, near the acid, not ions
-because only a few acid particles release H+ ions so at equilibrium, there will be more molecules of UNdissociated acid than disassociated acid molecules
what ions will HCL form when ionised
what about CH¬3COOH
which is ionised completely
H+ and CL-
H+ and CH¬3COO-
HCL is a strong acid so completely ionised
concentration is a measure of
what is ph
what is the strength of an acid dependant on
can you get a weak acid at high concentration, why
can you get a dilute but strong acid, why
how much acid there is in a certain volume of water (how watered down your acid is)
measure of concentration of H+ ions in the solution
the proportion of acid molecules that ionise , break apart, dissociate into H+ions
-weak bcse not all acid particles are dissociating, but high conc bcse there is a large proportion of acid particles per volume
-dilute because not highly concentrated (low number of dissolved acid molecules) but strong bcse all acid molecules ionise
what happens to pH when concentration of acid increases.
for a decrease of 1 on pH scale, what happens to concentration of ions
pH decreases
increases by factor of 10
pH scale
1 2 3 4 5 6 7 8 9
-ph moved from 5 to 3, the concentration of acid would….
-ph moved from 5 to 2, concentration of acid would…
-ph moved from 5 to 9, concentration of acid would…
multiply by 100
multiply by 1000
-be 10000 times lower
metal oxides / metal hydroxides are either a ……. or a………
what type of substance will react with an acid to get salt and water - neutralisation reaction
an alkali or a base
a base (inc alkalis- they are soluble bases)
acid + metal oxide=
acid + metal hydroxide=
Hydrochloric acid + copper oxide =
sulfuric acid + calcium hydroxide =
nitric acid + potassium hydroxide=
salt and water
copper chloride + water
calcium sulfate + water
potassium nitrate + water
what is a metal carbonate
acid + metal carbonate=
hydrochloric acid + sodium carbonate=
sulfuric acid + calcium carbonate =
what is the chemical formula for a carbonate
a base
salt + water + carbon dioxide
sodium chloride+ water + carbon dioxide
calcium sulfate + water + carbon dioxide
CO¬3 ²⁻
RP make SOLUBLE salt using INSOLUBLE base
- Measure acid (eg 20 cm3) into measuring cylinder, pour it into beaker.
- use Bunsen burner- gently heat acid
- Add insoluble base in small amounts so no more reaction, so its excess ( no more effervescence+ excess solid sinks).
- Filter( filter paper + funnel) to get salt solution
- Pour salt solution into evaporating basin.
- Evaporate solution w/ water bath OR electric heater till crystals start to form.
- Leave evaporating basin in cool place for 24 hours (min)
- filter + pat crystals dry w/ filter paper
RP making soluble salts-
safety precautions x3
why should you not overheat the salt solution
● Wear safety goggles eg when heating (as acid can be corrosive)●
● hair tied back.
● When Bunsen burner is not used, turn off / leave it on the orange safety flame.
-the crystals will break down and release harmful gases
What happens to metal atoms when react w/ other substances
Reactivity of metal depends on its…
Metals can be put in order of reactivity based on reactions with ……. or …… based on how ……. the reaction was
form + ions
tendency to form + ions
water/ dilute acids based on how vigorous the reaction was
reactivity series
*14
potassium people
sodium say
lithium lions
calcium cant
magnesium mingle
aluminium alongside
carbon charlies
zinc zebras
iron if
hydrogen he
copper cant
silver stop
gold growling
platinum
which metals will react w/ acids
What is carbon used for
metals more reactive than hydrogen
react it with a metal ore (metal less reactive than carbon) to extract the metal by reduction
acid + (some) Metal =
How can you tell the speed if the reaction
How do K, Na, Li, Ca react
Will Copper react with a cold dilute acid
what are the formulas for:
hydrochloric acid
nitric acid
sulfuric acid
salt + hydrogen
rate of hydrogen bubbles given off
React explosively
No
HCl (creates chloride salts)
HNO¬3
H¬2 SO¬4 (creates sulfate salts)
describe reactions of ….. and why
Mg + 2HCl
Mg+ H¬2SO¬4
Zn + 2HCl
Zn + H¬2SO¬4
Fe + 2HCl
Fe+H¬2SO¬4
What is made in these reactions
How can you speed up the reactions
Mg has vigorous reaction w/ (cold dilute) acids- loads of bubbles produced- much more reactive than H, very easily displaces
Zinc reacts quite rapidly w/ acids- more reactive than H, easily displaces
Iron reacts slower w/ acids- Only a bit more reactive than H
Mg + 2HCl / H¬2SO¬4 = Mg chloride/Mg sulfate + hydrogen
Zn + 2HCl / H¬2SO¬4 = Zn chloride/ Zn sulfate + hydrogen
Fe + 2HCl / H¬2SO¬4 = Fe Chloride/ Fe sulfate + hydrogen
Heat them up
How to confirm if H is formed when metal + acid react-
Metal + water =
metal + acid=
acid + metal oxide=
acid + metal hydroxide=
acid + metal carbonate =
Burning splint test
Metal + water =Metal hydroxide + hydrogen
metal + acid= Salt + hydrogen
acid + metal oxide= salt + water
acid + metal hydroxide= salt + water
acid + metal carbonate =salt + water + CO¬2
which metals will react with water
In what state are metals usually found, explain , x4
What process is this an example of
what reactions would be used to get a pure metal
metals above zinc in reactivity series
As compounds, not in pure form - as metal oxide ores - found in the ground, form compounds bcse they are fairly reactive
Example of oxidation
chemical reactions ( electrolysis/ reduction)
What is reduction w/ carbon
what is oxidised + what is reduced in reduction with carbon
How do u extract metals more reactive than carbon, a con of this
Where would the reduction of iron oxide w/ carbon take place-
What would be the products
In what state is gold found in earth
metals less reactive than carbon extracted from their ores by reacting w/ carbon(displacement)
Ore is reduced, Carbon is oxidised (in terms of Oxygen)
Electrolysis- expensive
in a blast furnace
Carbon dioxide + Iron
As metal itself
what is oxidation
what is reduction
If electrons are transferred in a reaction, what is the reaction called
oxidation= gain O2 / lose e-
Reduction = Lose O2/ gain e-
(OIL RIG for electrons)
REDOX rection (reduction+ oxidation happen at same time)
3 types of reactions that are redox
Explain why
metal + acid
metal atoms lose electrons+ become ions-oxidised by hydrogen ions
hydrogen ions gain electrons+ become atoms-reduced by iron atoms
Halogen displacement reactions( more reactive Halogen displaces less reactive one from a salt solution)
More reactive halogen gain electrons + become ions - reduced by ions of less reactive halogen
Less reactive halogen loses electrons+ become atoms- oxidised by atoms of more reactive halogen
Metal displacement-
put more reactive metal in solution of dissolved (less reactive) metal compound, more reactive will displace
what is the chemical equation for this metal displacement
Iron+ copper sulfate = iron sulfate + copper
Why is this a redox reaction?
what is always reduced/ oxidised in metal displacements
Fe + CuSO¬4 —-> FeSO¬4 + Cu
Iron loses 2 electrons + becomes 2+ ion
Copper ions gains these 2 electrons + becomes copper atom
Metal ion gains e- reduced
metal atom loses e- oxidised
do ionic compounds eg MgO or CaCl¬2 have an overall charge
What is the formula for ionic compound:
magnesium iodide ( Mg ion- charge of 2+) (iodide ion- charge of 1-)
Calcium hydroxide (Ca ion- charge of 2+) ( OH ion- charge of 1-)
no
MgI¬2 (no overall charge)
Ca(OH)¬2 (OH in brackets so the 2 applies to the whole hydroxide)
What do ionic equations do
-What is the ionic equation for :
Mg (s) + ZnCl₂ (aq) —-> MgCl₂ (aq) + Zn (s)
What is oxidised. what is reduced
Shows the particles that react + products they form.
-Find the changed charge for each
Mg—-> Mg²+
2Cl - —–> 2Cl - stays the same- spectator
Zn²+ ——-> Zn
cross out spectator ions, they don’t change. Add state SYMBOLS. charges on either side of brackets are the same.
Mg (s) + Zn²+ (aq) ——-> Mg²+ (aq) + Zn (s) =ionic equation
Mg (s) is oxidised
Zn²+ (aq) is reduced
if iron sulfate solution is green
copper is orange
copper sulfate solution is blue
iron is grey
what happens when iron displaces copper in a copper sulfate solution
solution changes from blue to green
iron gets coated in orange copper
(iron sulfate and copper made)
steps in electrolysis x6
1 electric current passed through electrolyte
2 Ions in electrolyte separate - move to oppositely charged electrodes, react, compound decomposes
3 +cat ions in electrolyte move to cathode
4 -an ions in electrolyte move to anode
5 Ions travelling to electrodes creates a flow of charge through electrolyte
6 Ions touch electrode -gain/lose e- -form uncharged elements. They are DISCHARGED at electrodes (from the electrolyte)
what is an electrolyte-
why can it conduct electricity
Where do +ve ions go - what happens
Where do -ve ions go, what happens
PANIC…..
What are electrodes made of
+ an important thing to remember
Molten/dissolved ionic compound -
bcse ions free to move in the liquid/solution.
The +ve go to cathode(-ve electrode) and are REDUCED(gain e-)
The -ve go to anode(+ve electrode) and are OXIDISED(lose e-)
Cathode attached to -ve terminal of a power pack
Anode- vice versa
Electrodes- conducting material eg metal/ graphite
should be inert so X react w/ electrolyte
In electrolysis of lead bromide what is produced at the:
cathode
anode
Bromine forms -ve ions
lead forms +ve ions
Which electrodes are the non metals produced @
Which electrodes are the metals produced @
Bromine at anode
Lead at cathode
Non-metal @ anode
Metal @ cathode
Why is electrolysis used to extract some metals from molten compounds x2
Con of electrolysis to extract metals - explain
If metal is too reactive to be reduced w/ carbon
Or reacts w/ carbon
-Very Expensive- lots of energy used to:
melt the ore/compounds
produce the current
How is aluminium manufactured
Why is a mixture used as electrolyte
What is cryolite
Describe the process x5
electrolysis of molten mixture of aluminium oxide (Al₂O₃) (from bauxite) + cryolite using carbon as the anode
Aluminium oxide has very high m.p, mixing w/ cryolite lowers m.p - REDUCES energy needed and cost
-aluminium based compound, lower mp than Al
Aluminium mixed w/ cryolite
The molten mixture has free ions(conducts electricity)
Al³+ ions go to -ve electrode. Gain 3 e- and become neutral Al atoms
The Aluminium atoms sink (molten Al on bottom of tank)
O²- ions go to +ve electrode. Lose 2 e- each and combine to O₂ molecules
What is used as the anode in electrolysis of Al₂O₃ + cryolite. Why
Why does anode need to be replaced continually
what direction do electrons flow from in electrolysis
Carbon eg graphite as its a good conductor and has high mp. Won’t melt
Oxygen produced reacts w/ carbon to produce CO₂ . Wears away anode
from anode to cathode
Equation at electrodes in Aluminium extraction
Cathode (-ve)
Anode (+ve)
Overall equation
Word equation and chemical equation + STATE SYMBOLS
Al³+ + 3e- —-> Al (reduction)
2O²- ——> O₂ + 4e- (oxidation)
Aluminium oxide —-> aluminium + Oxygen
2Al₂O₃ (l) ——> 4Al (l) + 3O₂ (g)
What ions are present in electrolysis of an AQUEOUS SOLUTION
The ions discharged at the electrodes depends on….
Reversible reaction for water w/ STATE SYMBOLS
what metal is good to use as electrode
the +ve and -ve ions from the ionic compound
H+ ions OH- ions from the water
- Depends on RELATIVE REACTIVITY of elements involved
H₂O(l) ⇌ H+(aq) +OH-(aq)
Platinum- inert, very unreacive
What happens in AQUEOUS solutions at …..
Cathode
Anode
CATHODE- if H+ and Metal ions present
-if metal is more reactive than Hydrogen, Hydrogen gas produced
-if metal is less reactive than Hydrogen, Solid layer of pure metal produced -will coat cathode
ANODE-
-if HALIDE Ions (Cl- Br- ect) present, Halogen formed
-If X halide ions present, OH- ions discharged. OXYGEN + WATER formed
What ions are in a solution of CuSO₄
What is made at cathode
What is made at anode
Half equation for cathode
Half equation for anode
Cu²+ SO₄²- H+ OH-
Cu produced - Cu less reactive than H, (coats electrode)
Oxygen + water produced- NO halide ions present.
Cu²+ + 2e—–> Cu
4OH- ——> O₂ + 2H₂O + 4e-
Half equation at anode if OH- ions are discharged
4OH- ——> O₂ + 2H₂O + 4e-
in electrolysis of aqueous solutions.
where does oxidation and reduction happen
What can be seen if O₂ produced
Oxidation at Anode
Reduction at Cathode
Bubbles( at anode)
set up for electrolysis if you want to collect the gas- 3 things
Safety precautions for electrolysis x2
inverted test tube filled w/ solution
electrodes inside test tube
gas produced at electrodes collects inside test tubes
● Safety goggles
● Room should be well ventilated - large quantities of chlorine gas is toxic
Usual way of electrolysis 6 steps
- Add vol of solution to a beaker. eg 50cm³
- insert electrodes through holes in lid (ensure electrodes X touch)
- Attach crocodile leads to electrodes. Connect rods to DC terminals of a low volt power supply.
- Turn power supply on eg 4V
- put litmus paper near anode w/ forceps
- turn on power + observe cathode
tests for chlorine, hydrogen, oxygen
What are 1/2 equations for
How do you get an ionic equation + important point to remember
Chlorine bleaches damp litmus paper ( Blue>White)
Hydrogen makes ‘squeaky pop’ w/ lighted splint
Oxygen relights glowing splint
Show reactions at the electrodes- gain/loss of e-
Combine 1/2 equations from both electrodes-
number of e- should be the same in each 1/2 equation so they cancel out and aren’t in ionic equation
What ions are in an aqueous solution of NaCl
What is made at cathode
What is made at anode
Half equation for cathode
Half equation for anode
Ionic equation
Na+ Cl- OH- H+
H₂ is made - Na is more reactive so stays
Cl₂ gas is made- it is a halogen
2H+ + 2e- ——> H₂
2Cl- ——> Cl₂ + 2e-
2H+ + 2Cl- ——-> H₂ + Cl₂
17 cm³ of HCl used to neutralise 25 cm³ sodium hydroxide (conc.0.1 mol/dm³) Calculate the concentration of the acid. Mr HCl= 36.5
HCl
NaOH
NaCl
H
