Master Cards Flashcards
Describe the structure of an ionic lattice
- Giant ionic lattice
- Regular arrangement of oppositely charged ions
Explain why an ionic lattice has a high melting point
- Strong electrostatic attraction
- Between oppositely charged ions
- Requires a lot of energy to overcome forces
Explain why an ionic compound conducts electricity when molten or dissolved but not when solid
- When molten or dissolved
- Ions are able to move freely
- And carry charge
Describe examples of simple (covalent) molecules
- Simple molecules contain only a few atoms held together by covalent bonds
- An example is carbon dioxide
- Which contains one atom of carbon bonded with two atoms of oxygen
Explain why simple molecules have a low boiling or melting point
- Weak intermolecular forces (between molecules)
- Which require little energy to overcome
Explain why Carbon Dioxide has a lower melting point than water
- Carbon dioxide has very weak intermolecular forces (between molecules)
- Water has stronger intermolecular forces between molecules
- Called hydrogen bonds
- Which require more energy to overcome
Describe the structure of different covalent bonds (diamond, graphite, fullerenes)
DIAMOND:
- Each carbon is covalently bonded to 4 other atoms
- Forming a giant covalent structure
GRAPHITE:
- Each carbon is covalently bonded to 3 other atoms
- Forming layers which are held together by weak intermolecular forces
- With delocalised electrons between layers
FULLERENES:
- Molecules of carbon atoms with hollow shape
- Their structures are based off of hexagonal rings of carbon atoms joined by covalent bonds
Explain why graphite conducts electricity but diamond doesn’t
- Graphite has delocalised electrons between layers
- Which are free to move and carry charge
- In diamond, the outer electrons are all shared in covalent bonds
Describe the structure of a metal
- Giant lattice
- Of positive metal ions (cations)
- Surrounded by a sea of delocalised electrons
Explain why metals have a high melting point
- There is a strong electrostatic attraction
- Between positive metal ions and delocalised electrons
- Which require lots of energy to overcome
What is a delocalised electron?
Electrons in a molecule, ion or solid metal that are not associated with a single atom or a covalent bond.
Explain why metals conduct electricity
- Sea of delocalised electrons
- Which can move and carry charge
Describe the structure of a polymer
A large molecules formed from repeating units called monomers
Describe the difference between Ar and Mr
- Ar is the relative atomic mass of an atom (it’s mass on the periodic table)
- Mr is the relative formula (molecular) mass of the compound, found by adding all the total massed of the elements in the compound
Describe how to calculate formula mass
Add the total masses of the elements together
Show how to balance equations using state symbols
State: Symbol: Further information:
Solid (s)
Liquid (L) Only water or molten substance
Gas (g)
Aqueous (aq) Aqueous means dissolved in water. Solutions such as hydrochloric acid are aqueous
Describe how to determine percentage by mass calculations
% mass = (total of Ar of the element / Mr of the compound) x 100
Describe how to calculate empirical formula of a compound
1) Write the element symbols
2) Write the masses
3) Write the Ar values
4) divide masses by Ar
5) Divide by the smallest number
6) Write the formula
Describe how to determine the molecular formula for a compound using it’s empirical formula
1) Write the empirical formula
2) Calculate formula mass from empirical formula
3) Divide M, by formula mass you calculated
4) Multiply empirical formula by answer
5) Molecular formula
Define what a mole is
- A mole is a unit for the amount of a substance
- 1 mole contains the same number of particles as there are atoms in 12.0g or carbon-12
Describe how to use Avogrado’s constant to determine the number of particles in a given number of moles of a substance
Avogrado’s constant - 6.02 x 10^23
No. Particles = Moles x Avogrado’s constant
State the formula for calculating the number of moles
Moles = mass(g) / Mr (or Ar)
Explain how to calculate the mass of a limiting reactant in a chemical reaction
Limiting reactant = The reactant that will run out first
1) Write out balanced equations
2) Calculate relative formula masses
3) Calculate the number of moles
4) Calculate the mass
Explain how to calculate concentration using mass or moles
Concentration = mass / volume
or
Concentration = moles / volume
Identify substances as acidic or alkaline using the pH scale
- Substances with a pH below 7 are acidic
- Substances with a pH above 7 are alkaline
Recall different indicators and their colour changes (phenolphthalein, universal, methyl orange, litmus)
Litmus Methyl Orange Phenolphthalein
Acid: Red Red Colourless
Alkali: Blue Yellow Pink
Litmus Methyl Orange Phenolphthalein
Acid: Red Red Colourless
Alkali: Blue Yellow Pink
Explain what pH is a measure of
- pH scale measures acidity (h+ Ion concentration)
- Each pH level below 7 shows a x10 increase in H+ ion concentration
- Each pH level above 7 shows a x10 increase in OH- ion concentration
State the products of the following reactions with acids:
1) Acid + Metals –>
2) Acid + Metal Oxide –>
3) Acid + Metal Hydroxide –>
4) Acid + Metal Carbonate –>
1) Acid + Metals –> Salt + Hydrogen
2) Acid + Metal Oxide –> Salt + Water
3) Acid + Metal Hydroxide –> Salt + Water
4) Acid + Metal Carbonate –> Salt + Water + Carbon dioxide
Describe the test for hydrogen gas
- Lit splint
- Squeaky pop sound
Describe the test for carbon dioxide
- Bubble through limewater
- Limewater turns cloudy
Describe how to measure the change in pH by adding calcium oxide (or hydroxide) to hydrochloric acid
1) Find pH of acid by dipping glass rod into a solution then touching to indicator paper (or use pH probe)
2) Add 0.3g calcium oxide and stir
3) Touch glass rod to indicator paper
4) Repeat until there is no further change in pH
Define the term electrolysis
Decomposing (splitting up) an electrolyte (ionic compound) using a direct current (electricity)
Describe what an electrolyte is
An ionic compound that is molten or dissolved
Explain why an electrolyte must be molten or dissolved in water to work
When molten or dissolved, ions are able to move around freely and carry charge
(when solid particles are locked in a giant ionic lattice)
Explain how ions are discharged at the cathode (-) electrode
- Positive ions are attracted to the cathode
- Where they gain electrons / are reduced
- To form either a solid metal or hydrogen gas
Explain how ions are discharged at the anode (+) electrode
- Negative ions are attracted to the anode
- Where they lose electrons / are oxidised
- To form a gas
Explain where oxidation and reduction occur during electrolysis
- Oxidisation is the loss of electrons
- Which occurs at the anode
- Reduction is the gain of electrons
- Which occurs at the cathode
State the reactivity series
Potassium Please
Sodium Stop
Calcium Calling
Magnesium Me
Aluminium A
Carbon Careless
Zinc Zebra
Iron Instead
Tin Try
Lead Learning
Hydrogen How
Copper Copper
Silver Saves
Gold Gold
Platinum
Predict the products of electrolysis of molten compounds e.g copper chloride
- Copper ions would be attracted to the cathode
- Where it is reduced and discharged
- Chloride ions would be attracted to the anode
- Where they are oxidised and discharged
(metal at cathode - non metal at anode)
Give examples of balanced half equations for the electrolysis of molten compounds at the anode and the cathode e.g. copper chloride
- Show the loss or gain of electrons
E.g. Copper ions (Cu2+) forming copper
Cu^2+ + 2e- —> Cu
Chloride ions forming gas
2Cl —> Cl2 + 2e-
Describe the practical method for the electrolysis of copper sulphate using:
a) Inert (carbon) electrodes
b) Non-inert (copper) electrodes
a)
- Pour copper sulphate solution into a beaker
- Place two graphite rods into the copper sulphate solution
- Attach one electrode to the negative terminal of a dc supply, and the other electrode to the positive terminal
- Turn on the power supply
- Test any gas produced with a glowing splint and a burning splint
b)
- Pour copper sulphate solution into a beaker
- Measure and record the mass of two pieces of copper foil
- Attach one to the negative terminal of the d.c. supply and the other to the positive terminal, and place in the copper sulphate solution
- Make sure the electrodes do not touch each other, then turn on the power supply
- Constant current
- Carefully remove electrodes, was with distilled water, then propane. Leave, so liquid evaporates.
- Measure and record the mass of the electrodes
- Repeat the experiment with fresh electrodes and different currents
Explain what is meant by ‘inert’ electrodes
Electrode - A conductive material
Inert - Un-reactive (does not take part in the reaction)
Describe what you would see during the electrolysis of copper sulphate using non-inert electrodes
- Red/Orange metal deposits (copper) at the cathode (increase in mass)
- Decrease in mass of the anode
- Deposits of impurities (sludge) under the anode
Predict and explain mass changed to non-inert electrodes during electrolysis
- The cathode would increase in mass
- As metal ions in the solution are attracted to the cathode
- Where they are reduced to form metal (deposits)
- The anode would decrease in mass
- As the metals are oxidised and leave the electrode
- Then enter the solution
Describe what you would see during the electrolysis of copper sulphate using inert electrodes
- Bubbles of gas (oxygen) forming at the anode
- Red-orange metal deposits (copper) at the cathode
Using the reactivity series, place: aluminium, carbon, copper, iron, hydrogen and gold into order or reactivity
Aluminium (most) Carbon Iron Hydrogen Copper Gold (least)
Describe what happens when a chemical is
a) Oxidised
b) Reduced
a) Oxidisation is the loss of electrons
b) Reduction is the gain of electrons
Identify the chemicals that is being oxidised and the chemical that is being reduced in this work equation:
Iron Oxide + Carbon Monoxide —> Iron + Carbon Dioxide
- Iron Oxide has been reduced (gained electrons / lost oxygen)
- Carbon Monoxide has been oxidised (lost electrons / gained oxygen)
Define the term ‘ore’
A rock that contains enough of a metal or a metal compound to make extracting the metal worthwhile
Work out the reactivity of metals by observing how they react with acid
- The more reactive the metal is
- The more violently is reacts with acid
- More fizzing/bubbling
- It may catch fire
Describe what happens during a displacement reaction
- A more reactive element will take the place of a less reactive metal
(the more reactive metal is oxidised, the less reactive element is reduced)
Use the reactivity series to explain why aluminium is extracted from it’s ore using electrolysis but iron is extracted from it’s ore by reduction with carbon
- Aluminium is more reactive than carbon
- So carbon is not strong enough reducing agent
- Iron is less reactive than carbon
- So carbon can reduce it
Explain why gold and silver do not require any extraction techniques
- Gold and silver are very un-reactive
- So are found native/uncombined in the Earths crust
Explain the advantages and disadvantages of recycling metals
Advantages:
- Less mining which causes noise and dust pollution
- Natural reserves last longer
- Less pollution
- Less metal waste in landfill
- Less energy needed to revelry metals rather than mine for them
Disadvantages:
- Can be expensive
- Energy is needed to transport and process it
Describe what life cycle assessment is
Life cycle assessments are used to judge the environmental impact of a product We need to consider: a) Where the materials come from b) Energy needed to make the product c) How it is transported d) How much energy is used when e) The product is used f) How we dispose of the products
Explain what bioleaching and phytoextraction are
Bioleaching: Certain bacteria can break down low-grade ores to produce an acidic solution containing metal irons
Phytoextraction: Plants grow on low-grade ore so they absorb metal ions Concentrate the ions Plants are harvested and burnt Leaving an ash with a high percentage of ore
Explain the benefits of biological methods of extraction
- Decontaminates the ground
- Conserves metal ores
- Allows use of low-grade ores
- Less noise due to mining / carbon neutral
