Chemical Changes Flashcards
Oxidation is the… of electrons
Loss
Reduction is the.. of electrons
Gain
How are highly reactive metals extracted
Electrolysis
Why are gold and silver found naturally as elements in the earth’s crust
They are unreactive
What is an ore
A rock containing a metal compound
In terms of oxygen what is oxidation
Oxygen added
In terms of oxygen what is reduction
Loss of oxygen
What type of metals can be extracted through reduction with carbon
Ones less reactive than carbon e.g iron, zinc and lead
(Carbon displaces them from their compound)
What is a spectator ion
Ion that is unchanged in a reaction
What does OIL RIG stand for
Oxidation is loss
Reduction is gain
Both in terms of electrons (it’s the other way round for oxygen)
2 chemical properties of most transition metals
Form ions with different charges
React slowly/ not at all with halogens, oxygen and water
What is electrolysis
Using electricity to extract elements from their compound
What is the electrolyte
The liquid/ solution containing ions and can conduct electricity
In electrolysis what is the electric current passed through
The electrolyte (liquid/ solution containing the ions)
Name for positive electrode
Anode
Name for negative electrode
Cathode
Can solid ionic compounds conduct electricity
No
Ions aren’t free to move and carry charge
Must be molten/ dissolved in water so ions are free to move
Why must the ionic compound in electrolysis be molten/ dissolved in water
Means ions are free to move and can carry charge (conduct electricity) and move to the electrodes
Which electrode do negative ions move to
Positive anode
Which electrode do positive ions move to
Negative cathode
What happens at the cathode for molten compounds
Cathode= negative so attracts positive metal ions
Metals gain electrons to form pure metal
What happens at the anode for molten compound
Anode= positive so attracts negative non-metal ions
Non metal loses electrons and becomes pure non-metal
In electrolysis which out of the metal and non metal forms positive ions, which forms negative
Metal- positive ions
Non-metal- negative ions
If sodium chloride undergoes electrolysis what will be formed at each electrode
Negative Cathode= sodium (metal)
Positive anode= chlorine (non- metal)
Which requires more energy, electrolysis of molten compounds or aqueos solutions
Molten- more energy required to melt ionic compound than dissolve it in water
What type of compound is electrolysis used for
Ionic
(must be molten/ dissolved in water)
In the electrolysis of aqueous solutions why aren’t the pure metals always produced
Water undergoes ionisation
Hydrogen can be formed at the cathode if less reactive than the metal
Oxygen and water can be formed at the anode from the hydroxide ions if a halide (e.g chlorine, iodine, bromine..) isn’t present
During electrolysis when is hydrogen produced
If it is an aqueous solution and the metal is more reactive than hydrogen
During electrolysis when is oxygen produced
If it’s an aqueous solution and no halide is present- hydroxide ions lose electrons at anode
When is electrolysis used to extract metals
If metal is more reactive than carbon (cannot be reduced by it)
Why is cryolite added to aluminium oxide during electrolysis
Lowers melting point- cheaper as less energy required
What are the electrodes made of during electrolysis of molten aluminium oxide
Graphite
Why must the graphite electrode be replaced regularly during electrolysis
Reacts with oxygen to form carbon dioxide so it’s slowly burnt away
What ions do acids release when dissolved in water
H+
What are the 3 main acids
Sulfuric acid, nitric acid, hydrochloric acid
True or false, acids and alkalis are both compounds
True
What ions do alkalis release when dissolved in water
OH-
True or false, the more H+ there are in a solution then the lower the PH
True as H+ is acidic
3 examples of strong acids (also the 3 main acids)
Hydrochloric
Sulfuric
Nitric
What happens to strong acids when they dissolve in water
They are completely ionised
Every molecule splits up into ions
Which out of strong and weak acids are completely ionised when dissolved in water
Strong acids
E.g hydrochloric, nitric and Sulfuric
What does completely ionised mean
All molecules split up into ions
E.g strong acids when dissolved in water
What happens to weak acids when dissolved in water
They are partially ionised
Only some of their molecules split up into ions
For a given concentration the stronger the acid the….. the pH
Lower
Which out of strong acids and weak acids are completely ionised and which are partially ionised when dissolved in water
Strong= completely ionised (all molecules split up into ions)
Weak= partially ionised (only some molecules split up into ions)
Which out of concentrated or dilute acids will have lots of acid in a small volume of water
Concentrated
(Dilute acids have little acid in a large volume of water)
…acids have lots of acid in a small volume of water
Concentrated
…acids have little acid in a large volume of water
Dilute
Describe a dilute strong acid
Few acid ions (dilute)
They are completely ionised (strong acid)
Describe a concentrated strong acid
Lots of acid ions (concentrated)
Completely ionised (strong)
Describe a dilute weak acid
Few acid ions (dilute)
Partially ionised (weak)
Describe a concentrated weak acid
Lots of acid ions (concentrated)
Partially ionised (weak)
What do acids reacting with metal/ metal compounds form
Salts
Complete equation
Metal + acid->
Salt + hydrogen
Complete equation
Metal hydroxide + acid->
Salt + water
Complete equation
Acid+ metal oxide->
Salt + water
Complete equation
Acid + metal carbonate->
Salt+ water+ carbon dioxide
True or false when metal hydroxides and metal oxides react with acid they both form a salt + water
True
Alkali vs base
Both neutralise acids to form water in neutralisation reactions
If they dissolve in water (forming alkali solutions) they’re called alkalis
True or false alkalis are a type of base (neutralise acid to form water) that dissolve in water
True
What does crystallisation produce
Solid salt (from an insoluble base)
Process of crystallisation
Put fixed volume of dilute acid into flask (using measuring cylinder) and heat gently with Bunsen burner
Add small amount of base and stir
Keep adding base until no more reacts (it’s now in excess)
Filter to remove unreacted base
Add remaining solution to evaporation dish and place on top of water bath over Bunsen burner
Water will be evaporated leaving behind salt crystals
How can you obtain a solid salt from a solution
Crystallisation
2 ways PH can be measured and which is more accurate
Universal indicator
Probe
Probe more accurate as exact decimal number
What does copper oxide look like
Black powder
When making crystals why should the acid be heated
Speeds up reaction
For titrations why should you use a pipette not a beaker to measure the fixed volume of the unknown concentration
More accurate as it has a better resolution (smaller scale)
When carrying out a titration why should you place a white tile under the conical flask
To see a clearer colour change
What is a concordant result
Results within 0.1cm cubed of each other
(When carrying out titrations)
Describe a 6 mark method for carrying out a titration (remember in an exam you will have to use information from the question to know which is the ‘known/ unknown’ concentration
1) With a pipette measure a fixed volume of unknown into a conical flask (place conical flask on white tile to be able to see clearer colour change)
2) Add 2-3 drops of indicator (methyl orange/ phenolphthalein) to conical flask and swirl
3) Add known to burette with tap off
4) Turn on tap and add the known into the unknown in the conical flask (swirling flask whilst doing so) until a colour change occurs
5) This is the first rough titration and has gone past the ‘end point’
6) Carry out another titration but start adding drop wise as you approach the end point and swirl in between until the color change (neutralisation) has occurred
7) Keep carrying out titrations until you have 3 concordant results (ignore anomalies)
When should you stop carrying out titrations
Once you have 3 concordant results
Describe how to make a pure, dry sample of soluble salt using a dilute acid and insoluble metal oxide/ carbonate) (use information in question as to what metal oxide/ metal carbonate to use and which acid to use)
1) measure fixed volume of acid in beaker and gently heat over Bunsen burner until almost boiling
2) Use a spatula to add small amounts of the oxide/ carbonate (powder) to the acid and stir using a glass rod to form a solution
3) keep adding one spatula at a time until the oxide/ carbonate is in excess (when some powder still remains after stirring)
4) Use a filter funnel and filter paper to filter out the insoluble carbonate/ oxide and collect the filtrate (reacted solution) in a conical flask
5) place the solution in an evaporating basin and place on a water bath over a Bunsen burner
6) Stop heating when half the solution has evaporated and crystals have started to form around the edge of the basin
7) Leave the remaining solution in a cool place for 24hrs to allow crystals to form
8) Gently pat crystals dry with paper towel
2 hazards of making soluble salts RPA
Bunsen burner and hot apparatus
Concentrated acid
Possible harm of concentrated acid (hazard) in making soluble salts RPA and safety precaution to address hazard
Corrosive and damages skin and clothes.
Use dilute acid and wear goggles
Why should a dilute not concentrated acid be used in making soluble salts RPA
Concentrated acid is corrosive and can damage skin and clothes
Why is the Bunsen burner and hot apparatus a hazard in the making soluble salts RPA and what safety precaution can be taken
Tie back hair and roll up sleeves to prevent them catching fire
Do not touch hot equipment to prevent burning yourself
For making soluble salts RPA why do you gently heat the acid before adding the oxide/ carbonate
Increase rate of reaction
Ensure all oxide/ carbonate will react
3 key scientific processes occurring in making soluble salts RPA
Filtration (filter out excess oxide carbonate from solution)
Evaporation
Crystallisation (crystals forming)
Describe how to carry out the electrolysis of an aqueous solution (in this example use copper chloride)
1) Place copper chloride solution Into a beaker
2) place plastic Petri dish over beaker with 2 holes in
3) Insert graphite rod into each hole (electrodes)- electrodes must not be touching or it will produce a short circuit
4) Attach a crocodile clip to each rod and connect them to a low voltage power supply using wire
5) Switch on the power supply with 4V
6) The anode should start to become coated in copper
7) At the anode gas bubbles should appear + smell of chlorine in air
8) Hold a damp piece of blue litmus paper at the anode and it should become bleached (proves that chlorine gas is being formed)
What would be different when carrying out the electrolysis of copper chloride compared to sodium chloride (solutions)
For copper chloride copper is formed at cathode
For sodium chloride hydrogen is formed so gas bubbles will form at cathode (we can prove that the gas is hydrogen by collecting it and testing it with a lit splint- it should produce a squeaky pop)
For both bubbles of chlorine gas should form at the anode (chlorine can be tested as it should bleach damp blue litmus paper)
During electrolysis how can we tell if chlorine has been produced at the anode
Bubbles
Smell of chlorine in air
Bleaches damp blue litmus paper
In a titration what do you use to measure a fixed volume of the unknown concentration into the conical flask
Pipette
What does chlorine do to damp blue litmus paper
Bleaches it
How to test for hydrogen gas
Place lit splint in test tube containing gas
If hydrogen is present it will produce a squeaky pop
True or false, transition metals form ions with different charges
True
True or false, transition metals have high melting points
True
How to collect gas produced in electrolysis
Place test tube over electrode (or measuring cylinder is measuring volume)
Why blue colour of copper sulphate solution becomes paler in electrolysis
Copper ions are removed
