C4 Chemical Changes Flashcards
Examples of pH’s
pH 0-1 stomach acid 2 - vinegar or lemon juice 4 acid rain 6 normal rain 8 washing up liquid 10 pancreatic juice 11 bleach
What is an indicator
Dye that changes colour depending on whether it’s above or below a certain pH
Wide range indicators have many dyes - gradually change
What is an acid
A substance that forms an aqueous solution with a pH less than 7
What’s a base
Substance with pH greater than 7
Chemical reaction for neutralisation
Acid + base -> salt + water
What happens when an acid neutralises a base
All products are neutral
What do acids produce in water
Produce protons - they ionise in aqueous solution and produce hydrogen ions
H+ ion is a proton
What’s a strong acid
Strong acids ionise completely in water - acid particles dissociate to release H+ ions (sulphuric, hydrochloric and nitric
What are weak acids
Weak acids (ethnicm citric and carbonic) don’t fully ionise in water - only small proportion dissociates to form H+ ions Ionisation of a weak acid is a reversible reaction - equilibrium between undissociated and dissociated acid. As there’s only a few H+ ions, equilibrium lies left
Why are strong acids more reactive
As the concentration of H+ ions is higher, rate of reaction is quicker
What is pH a measure of
Measure of concentration of H+ ions
Every decrease of pH 1 - concentration of H+ ions increase by factor of 10
pH 4 has 10x concentration of H+ ions than pH 5
Decrease by 2 - H+ increase by factor of 100
What is acid strength
Tells you what proportion of acid molecules ionise in water
What does concentration measure of acid
How much acid there is in a certain volume of water
pH decreases with increasing concentration no matter the strength
What are metal oxides and hydroxides
They’re bases that sometimes dissolve in water and these soluble compounds are alkalis
Chemical Reaction for acids and metal oxides or acids and hydroxides
Acid + metal oxide -> salt + water
Acid + hydroxide -> salt + water
What does the salt produced depend on
Depends on acid and metal ion
E.g
Hydrochloric acid + copper oxide -> copper chloride + water
Acid and what produces CO2
Acid and metal carbonates produce CO2
Metal carbonates are also bases
Chemical reaction for acids and metal carbonates
Acid + metal carbonates -> salt + water + carbon dioxide
E.g
Sulphuric acid + calcium carbonate -> sulphuric carbonate + water + carbon dioxide
What can you make soluble salts with
Insoluble bases -> need to pick right acid and insoluble base - like insoluble metal oxide, hydroxide or carbonate
Warm dilute acid
Add insoluble base bit by bit until no more reacts - neutralised = solid sinks
Filter excess solid
Gently heat with water + let cool- salt crystals should form - filtered from solution and dried - crystallisation
What is reactivity based off of
How easily an atom looses electrons and forms ions
Higher up in reactivity series = more easily they form positive ions
List the reactivity series from most to least
Potassium, sodium , lithium, calcium, magnesium, carbon, zinc, iron, hydrogen, copper
Metals also react with water - chemical reaction
Metal + water -> metal hydroxide + hydrogen
Speed of reaction is indicated by rate at which…
Bubbles of hydrogen are given off
More reactive metal = faster reaction
Lots of metals react with oxygen to form…
Oxides through oxidation.
What are Oxides often
Often ores that metals need to be extracted from
What’s a reduction reaction
Separate metal from oxide
Formation of metal ore
Oxidation = gain of oxygen
Extraction of metal
Reduction = loss of oxygen
Some metals can be extracted by….
Reduction with carbon
Some metals extracted from ores chemically by reduction using carbon
What happens during reduction using carbon
Ore is reduced as oxygen is removed from it, and carbon is oxidised
E.g Iron(III)Oxide + Carbon -> iron + carbon dioxide
How can metals higher than carbon be extracted
Extracted with electrolysis
How can metals below carbon be extracted
Reduction by carbon - as carbon can only take away oxygen from metals less reactive than itself > displacement
Why is gold mined in its elemental form
Some metals are so unreactive so they are in earth as the metal itself
What’s a redox reaction
If electrons are transferred, it’s a redox reaction
What is OIL RIG
oxidation is loss (of electrons)
Reduction is gain (of electrons)
Oxidation and reduction also used in terms of oxygen
REduction and OXidation Happen…
At the same time > RED-OX
Displacement reactions are…
Redox reactions
What do displacement reactions involve
Involve one metal kicking the other out - > more reactive metal will displace the less reactive metal from its compound
E.g iron + copper Sulfate -> iron Sulfate + copper
Iron looses 2 electrons - oxidised
Copper gains two to become Copper atom - reduced
What are ionic equations
Show useful bits of reactions
What’s in an ionic equation
Contains only the particles that react are shown
E.g the displacement but not the stuff that doesn’t change
What is electrolysis
Splitting up of electricity
What happens during electrolysis
An electric current is passed through an electrolyte
Ions move towards electrodes where they react and the compound decomposes
Positive ions in electrolyte will move toward the cathode (-ve electrode) and gain electrons
Negative ions will move toward anode (+ve electrode) and lose electrons
Creates flow of charge through electrolyte as ions travel to electrodes
As ions gain/lose electrons they form uncharged elements and are discharged from the electrolyte
What’s an electrolyte
Liquid of solution which can conduct electricity
What’s an electrode
Solid that conducts electricity and is submerged in electrolyte
What does electrolysis of molten ionic solids form
Forms elements
An ionic solid can’t be electrolysed because ions in fixed positions and can’t move
Molten ionic compounds can be electrolysed as ions can move freely and conduct electricity
Molten ionic liquid e.g lead bromide are always broken up into their elements
Positive metal ions reduce to element at cathode
Negative non-metal ions oxidised to element at anode
How can metals be extracted from ores with electrolysis
Method is very expensive as lots of energy required to melt ore and produce required current
1. Aluminium extracted from bauxite by electrolysis
2. Aluminium oxide has high melting point - mixed with cryolite to lower point
3. Molten mixture contains free ions - conductor
4. Positive Al3+ Ions attracted to negative electrode where they pick up 3 electrons and turn into neutral aluminium atoms - sink to bottom of tank
5. Negative O2- ions attracted to anode and loses 2 electrons -> neutral oxygen atoms combine to form O2 molecules
Aluminium -> Aluminium + oxygen oxide
At cathode Al3+ + 3e- —> Al
At anode 2O2- —> O2 + 4e-
What happens during electrolysis of aqueous solutions
In aqueous solutions, there is H+ and OH- ions from water
At cathode if H+ ions present > hydrogen gas produced if the metal forms an elemental metal that is more reactive than hydrogen
If metal ions form elemental metal that is less reactive than hydrogen -> solid layer of pure metal produced
At anode if OH- and halide ions(Cl-, Br-, I-) present, molecules of chlorine, bromine or iodine are formed.
No halide ions - OH- ions discharged and oxygen formed
Examples on C4 loose sheet