chemical changes- topic 4 - EOY10

Nov-feb

reactivity

how easily electrons are lost/gained

(nothing to do with melting/boiling)

oxidation

process of gaining oxygen

e.g 2mg + O(2) → 2MgO

in electrolosys- loss of electrons

reduction

the loss of oxygen

e.g 2MgO →2Mg+O(2)

in electrolosys- gaining electrons

displacement reaction

where a more reactive metal displaces a less reactive metal from its compound

what do the roman numerals show on the transition metals

eg. Iron (II) chloride

to show the charge of transition metals

FeCl(2)

why is potassium more reactive than lithium (3)

-atoms get bigger down the group

-less attraction between the nucleus and the outer electron

-easier to loose an electron so more reactive (opposite for group7)

how do we explain the different reactivity’s of metals

-for a metal atom to react it must loose electrons to become a postitive ion.

-the easier an atom can do this,the more reactive the more reactive the metal will be

reactivity series

potassium (k)

sodium (Na)

Lithium (Li)

Calcium (Ca)

Magnesium (Mg)

Aluminium (Al)

Carbon (C)

Zinc (Zn)

Iron (Fe)

Hydrogen (H)

Copper (Cu)

Silver (Ag)

Gold (Au)

ore

a rock containing an ionic metal,compound,usually a metal oxide

how is iron extracted

-reduction with carbon

-carbon and iron ore (iron oxide) are heated to a very high temp in a blast furnace →iron is reduced- iron oxide + carbon →iron +carbon dioxide

-very wasteful

-bioleaching + phytomining produce solutions containing copper

-so you have to do electrolisis or displacement with scrapirion

how does pytomining work (4)

1. copper ions in soil are abdorbed by plants roots

2. copper ions become part of the plant

3. plant is burned-copper ions join with oxide ions in the air (forms copper oxide, CuO)

4. ash containing copper oxide reacts with sulfuric acid then filtered-makes copper sulfate solution- ash is dissolved -electrolysis of cop sul solution copper metal collects at neg electrode

advantages(6) and disadvantages(6) of phytomining

advantages

-uses low grade copper ore

-less energy than smelting

-less air polution produced

-less waste rock

-decontaminates polluted ground

-produces less greenhouse gases then smelting

disadvantages

-can produce toxic chrmicals

-a lot slower

-electrolysis requiress lots of energy (and money)

-plants need good growing conditions

-don’t get much-lower yield

-dependent on weather

how does bioleaching work (3)

-bacteria are used to extract copper ions from low grade copper ores

-bacteria converts copper compounds within ores into solution

-these copper compound solutions can be separated with electrolysis or displacement reactions to form copper metal

advantages and disadvantages of bioleaching

advantages

-economical→simpler,cheaper

-environmental→less landscape damage- bacteria grows naturally

-ore conservation→can eextract metals from ores that are too poor for other technologies

-low grade ores

-produces less air pollution than smelting

disadvantages

-economical-even slower compared to smelting-less profit

-environmental-toxic chemicals are produced →heavy metal ions leak during acid mine drainage

pros/cons of smlelting (1,2)

pro

-have equiptment already/know how it works

cons

-lots of equiptment is used

-produces lots of CO(2)

Pros/cons of mining (2,3)

pros

-creates jobs

-we know how it works/have equiptmwnt already

cons

-lots of waste

-very noisy

-can destroy habitats

acids

aqueous solutions that can obtain hydrogen ions (H+)

bases

chemicals that neutralise acids

alkalines

bases that form hydroxide ions (OH-) in aqueous solution

when are salts formed

when the hydrogen ion (H+) in an acid is replaced by a positive ion from a base

making salts

(general equations to learn,how to work out name of salt)

-most involve the neutralisation of an acid

1. acid +metal →salt + hydrogen

2. acid + alkali/base → salt + water

3. acid + carbonate → salt + water + carbon dioxide

4. acid +metal oxide → salt + water

how to work out name of salt

first part→from the base and is a metal

second part→ from the acid

e.g hydrochloric acid + sodium hydroxide → sodium chloride

why can’t we use all of these methods for making a salt using the required practical

matals, metal oxides and metal carbonates are insoluble bases so we can “see“ when they are in excess (all acid is neutraalisied) we can filter the excess to remove it

metal hydroxides are alkalis (soluble bases) so we can’t “see” when acid is fully neutralised or could we use filtration to remove excess alkali

how to make a pure dry salt

Mix-

• measure acid using a measuring cylinder and pour into a beaker

• add the base (metal oxide/carbonate) into the acid until no more reacts (all acid has reacted so we say the base is in excess)

filter-

• filter using filter paper and funnel to remove the unreacted solids (excess base) leaving only the salt solution

crystalise-

• pour into an evaportating dish

• heat gently (safely) using a water bath (dont say budsen burner)

• evaporate MOST of the water then leave to cool to form crystals

purify-

• remove all crystials and rinse them

• pat dry crystals

why wouldnt i use a metal hydroxide when making salt

• beacsue its soluble|!!- can only use if insoluble

• need to get rid of excess

ionic equation for neutralisation

H+(aq) + OH-(aq) → H₂O(l)

dont forget state symbols!!

neutralisation

the neutralisation of an acid can bee “seen“ if we use an indicator

indicator-changes colour with a change in pH

-universal indicator is a mixture of indicators so cant be used for this practicle

end point

point when neutralisation occurs

how do indicators work

-indicators cgange colours- from acid to alkali

the acid and alkali are neutralised

what colour is the indicator thymol blue when its an acid, alkali and at its end point

acid→ yellow

alkali→ blue

end point→ green

what colour is the indicator phenolphthalein when its an acid, alkali and at its end point

acid→colourless

alkali→pink

end point→ pale pink

what colour is the indicator methyl orange when its an acid, alkali and at its end point

acid→red

alkali→yellow

end point→peach/orange

titrations

-the volumes of acid and alkali solutions that react with each other can be measured by titration using a suitable indicator

titration method (9)

1. use a funell to fill up a burette with the solution of known concentration- take funnel out after so no extra liquid is added

2. use a pipette and bulb to transfer the solution with thw unknown concentration into a conical flask

3. add indicatir to flask

4. stir. place flask on a white tile (so you cvan see the colour change later) under the burette

5. gradually add solution from the burette into the conical flask

6. swirl after each addition-stop as soon as misture in flask changes colour

7. recored how much solution was added

8. repeat until 2 measurements within 0.1³ are obtained

9. calculate mean volume of solution added for nuetralisation to occur

what is the pH scale

a logarithmic scale

a measure of concentration of hydrogen ions in a solution, H(aq)

acids are small covalent molecules until they are dissolved in water (aq) and form ions

pros and cons of ph probe (3) (1)

pros

more accurate

objective

measures continually

cons

expensive- needs calibration/trainig

pros/cons of univeral indicator (2)(2)

pros

cheaper

easy to use

cons

less accurate

subjective

concentration

(+how to calculate)

the mass of solute in a given volume of solution- measured in g/dm³

to calculate concengtration → mass divided by volume

weak acids

partially ionise in a solution

strong acids

fully ionise in aqueous solution

what type of acid are these?

qijfw

when does electrolysis happen

when an electrical current is passed through an ionic compound

whats an electrolyte

the ionic compound being broken down during electrolysis

what are the electrodes

the rods the current flows into the electrolyte

what are the ions turned into during electrolysis

the ions are turned back into elemants

whats a positive electrode called

whats a negative electrode called

anode

cathode

where do the + metal ions go to

where do the - metal ions go to

-cathode

+anode

what are the parts of the electrolysis equiptment

be able to lable electrolosis equiptment

power supply, ammeter/bulb, beaker, cathode (-electrode), anode (+electrode), electrolyte

why do you need an ammeter/bulb in the electrolysis apparatus

so you know that the current is flowing through the circuit

why does the ionic compound have to be molten (melted) OR dissolved in water (solution,aq) in the electrolysis equiptment

becasue the ions need to be free to move

solution

a mixture where a substance is dissolved in a solvent

solute

the substance being dissolved

solvent

the liquid part of a solution

soluble

describing a solid that is able to dissolve

dissolving

a process where a substance mixes with a liquid to form a clear solution

what happens at electrodes (2)

-the negative electrodes (cathode) attracts the zinc ions as zinc is positive and opposites attract

-the positive electrode (anode) attracts the chloride ion as chloride is negative and opposites attract

is oxidation the loss or gain of electrons

is reduction the loss or gain of electrons

loss

gain

O-oxidation
I-is
L-loss of electrons
R-reduction
I-is
G-gain of electrons

at the cathode

are the metal ions gained or lose electrons to form metals

gained

so its reduced

at the anode

non metal ions lose or gain electrons to form elements (gas molecules)

lose

it is oxidised

where do positive ions become elements

where do negative ions become elements

cathode

anode

what do half equations and ionic equations come in

pairs-they made an ionic equation when added together

the electron in each pair must cancel out to make the ionic equation

when is electrolysis used to extract a metal from its ore

if the metal is too reactive to be displaced by carbon (smelting) e.g aluminium

extraction of aluminium by elelectrolysis

rules for cathode (+ ions)

the least reactive element will be discharged

If the metal is more reactive than hydrogen water will form hydrogen gas (observe bubbles)

otherwise metal ions will form that metal

so

if the metal is more reactive than hydrogen- then hydrogen formed

if not- metal formed

Rules for anode

a solution containing a metal halide (g7) will produce that halogen gas

any other solution- the water will produce oxygen gas

are there halide ions

yes-halogen formed

no-oxygen formed

what do you observe and what gas is present when a glowing splint held in a test tube

observation-splint relights

oxygen is present

what do you observe and what gas is present when a lighted splint held in a test tube

pop sound heard

hydrogen is present

what do you observe and what gas is present when gas bubbles through lime water

lime water turns milky/cloudy white

carbon dioxide is present

what do you observe and what gas is present when damp litmus paper held in a test tube

pper bleached white

chlorine is present

formular for hydrochloric acid

HCL

formukar for sulfuric acid

H₂SO₄

formular for nitric acid

HNO₃

formular for sodium hydroxide base

NaOH

formular for calcium carbonate

CaCO₃

why do you swirl the conical flask when doing titration

you add the acid from the burette in order to evenly distribute it, and ensure that the colour change occurs as soon as neutralisation takes place.

why do you place the coniical flask on a white tile on the titration practical

so you can more easily see when the colour change takes place.

what iondoes acid form in water

H+

what ion does alkali form in water

OH-

how do you make a soluble compound into an electrolyte

dssolve in water

produces H+ and OH- as well