Chemistry Topic 1

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Describe a solid.
Strong forces of attraction between particles, holding them close together in a lattice arrangement. Keep a definite shape and volume.
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Describe a liquid.
Weak force of attraction between particles, randomly arranged and free to move past each other. They tend to stick closely together.
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Describe a gases.
Very weak attraction, free to move and are far apart. They do not keep a definite shape or volume.
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Define diffusion.
The gradual movement of particles from places where there are lots of them to places where there are fewer of them.
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Experiment to show diffusion with water.
Potassium Maganate(VII) and Water. Beaker of water, place some potassium manganate at the bottom. The purple colour slowly spreads out.
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Experiment to show diffusion with hydrogen chloride.
Aqueous ammonia (NH3) gives off ammonia gas. HCl gives off hydrogen chloride gas. White ring of ammonium chloride forms in the glass tube. (Cotton wool ball of each element either side of glass tube).
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Experiment to show diffusion with air.
Bromine gas is brown. Fill a gas jar half full of bromine gas, other half full of air. Separate the gases with a glass plate. Remove the plate, see the brown move through the tube.
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Nucleus of an atom.
Middle of the atom, protons and neutrons. Positive charge (because of the protons).
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Electrons in an atom.
Move around nucleus in shells, negatively charged.
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Charges of atoms.
Proton- relative mass = 1, relative charge = +1. Neutron- relative mass=1, relative charge =0. Electron- relative mass=1/2000, relative charge= -1.
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Number of electrons equals number of protons.
.
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What are elements?
One type of atom only.
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What are compounds?
A compound is a substance that is made of two or more different elements which are chemically bonded together.
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What are mixtures?
No chemical bond between the different parts of a mixture. The parts can be separated out by physical methods such as distillation.
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Filtration.
Used if your product is an insoluble solid that needs to be separated from a liquid reaction mixture. It can be used in purification.
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Crystallisation.
Separate a soluble solid from a solution. Pour solution into an evaporating dish, slowly heat (some solvent will evaporate, solution gets more concentrated). Stop when crystals start to form. Remove dish from heat,leave in warm place to evaporate+dry
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Using filtration and crystallisation to separate rock salt.
Rock salt is a mixture of salt and sand. Both are compounds, salt dissolves in water and sand doesn't. Grind up rock salt with pestle and mortar, dissolve in beaker and stir. Filter through filter paper in funnel, evaporate in an evaporating dish.
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Paper chromatography.
Line at bottom filter paper- using a pencil, insoluble. Spots of different dyes, regular intervals. Loosely roll sheet up and put it in a beaker of solvent. Dyes aren't touching solvent- don't want to dissolve.Solvent seeps up carrying dyes. Rate.
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How does chromatography separate mixtures?
Different dyes move up the paper at different rates. Some will stick to the paper and others will dissolve more readily and travel more quickly. Distance travelled depends on the solvent and paper used.
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How can chromatography identify dyes?
Make chromatograms, compare to what dyes are in unknown chromatogram to known. They will match if they're the same type.
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Simple distillation.
Separate a liquid from a solution. Solution heated, lowest boiling point part evaporates. Vapour is cooled, condenses and is collected. Solution remainders left behind in flask. Only use with different boiling point solutions.
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Fractional distillation.
Mixture of liquids. Mixture in flask, fractionating column on top. Different liquids will have different boiling points. Liquid with lowest evaporates first. Collect, new glass, move on. Raise boiling point until all collected.
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Periodic table.
Atoms shown in order of increasing atomic number. Elements with similar properties form columns. Elements in the same group have the same number of outer electrons.
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What are group 1 metals called?
Alkali metals.
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What are group 7 elements called?
Halogens.
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What are group 0 gases called?
Noble gases.
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Electron shells.
Lowest energy levels (shells) are always filled first, ones closest to the nucleus. 1st shell: 2, 2nd shell:8, 3rd shell:8.
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Ionic bonding.
Transfer of electrons. Lose or gain to form charged particles (ions), strongly attracted to one another. Attraction is called electrostatic attraction.
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What is oxidation?
When an atom loses electrons.
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What is reduction?
When an atom gains electrons.
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Group 1 and 2 elements - ionic bonding.
Metals, lose electrons to from +ve ions (CATIONS).
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Group 6 and 7 elements - ionic bonding.
Non-metals, gain electrons to form -ve ions (ANIONS).
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Ionic compounds drawing.
Dot and cross diagram.
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Giant ionic structures.
High melting and boiling points. Closely packed 3D lattice arrangement, electrostatic attraction between oppositely charged ions is very strong. Lot of energy needed to overcome the strong attraction. Charges- stronger forces of attraction if 2+.
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Covalent bonding.
Shared pair of electrons, both have a shared pair of electrons. Enough covalent bonds to fill up its outer shell. Strong attraction between the shared electrons, and the nuclei of atoms involved.
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Simple molecular substances.
Atoms within a molecule held together by strong covalent bonds.Forces of attraction between molecules in weak. Melting and boiling points are low, easily parted.
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Giant covalent structures.
No charged ions, all atoms bonded by strong covalent bonds. Very high melting and boiling points, don't conduct electricity. Insoluble in water.
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Diamond.
Four covalent bonds, very rigid structure. Hardest natural substance, used for drill trips and cutting.
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Graphite.
Three covalent bonds, layers slide over each other. Useful as a lubricant, leaves free electrons, good conductor of electricity.
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Balancing Equations.
Same number of atoms on both sides. Balance symbol equations by putting numbers in front of the formulae where needed. Balance one type of atom at a time.
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Define isotopes.
Different atomic forms of the same element, which have the same number of protons but different numbers of neutrons.
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What is relative atomic mass?
How heavy different atoms are compared with the mass of an atom of carbon-12. (eg carbon-12 has an Ar of 12). It's the average mass of all the isotopes of an element, it has to allow for the relative mass of each isotope+its relative abundance.
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What is relative abundance?
How much there is of each isotope compared to the total amount of the element in the world.
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What is relative formula mass?
A compound which has all the relative atomic masses of the atoms it contains added together.
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Finding the empirical formula (from masses or percentages).
List all elements in compound, underneath write experimental masses/percentages, divide each by Ar of that element, make a ratio in its simplest form = empirical formula of compound.
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Define empirical formula.
The simplest formula that tells you the ratio of different elements in the compound.
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Define molecular formula.
The actual number of atoms of each element in a single molecule.
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How do you find the molecular formulae?
Mass of empirical formula, find empirical units in the molecule, molecular formula is empirical units multiplied by empirical formula.
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Calculating masses in reactions.
Write out balanced equation, relative formula mass of two bits you want and multiply them by the balancing numbers in the equation. Divide to get one, then multiply to get wanted quantity.
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Percentage yield formula.
( Actual yield (grams) / theoretical yield (grams) ) x 100
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Number of moles formula.
Mass in g (of element or compound) / Mr (of element or compound)
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Avogardo's number.
The number 6.023x10^23. A mole is Avogadro's number of particles in a substance.
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What is water of crystallisation?
Solid salts consist of a lattice of +ve & -ve ions. H2O molecules incorporated too sometimes. A solid salt containing water of crystiallisation is hydrated, if a salt doesn't contain any water of crystallisation its anhydrous.
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How to calculate how much water of crystallisation a salt contains.
Work out the mass of what you have. Calculate the number of moles of water lost. Calculate the number if anhydrous salt made. Work out the ratio of moles of anhydrous salt to moles of water. X must be a whole number, round to result.
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Avogadro's Law.
One mole of any gas always occupies 24dm^3 at room temperature and pressure.
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Formula to convert the number of moles of any gas to volume.
moles of gas x 24. OR, (mass of gass/Mr of gas) x 24.
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Calculating the volumes in reactions with known masses.
Balanced equation, Mr for each, divide for one, times by all. Volume= (Mass/Mr) x 24.
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Concentration.
Usually measured in moles per dm^3.
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Formula for concentration.
number of moles / volume.
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Converting moles per dm^3 to grams per dm^3.
Divide the mass of the chemical in grams by the volume of solvent used to dissolve it in dm^3.
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What is electrical current?
A flow of electrons or ions. Electrons have a negative charge, ions can have either a +ve or -ve. Electrons and ions act as charge carries, they can move charge around a system to create a flow of electricity. The electric current is the flow of them
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When can ionic compounds conduct electricity?
When molten or in solution. Solid ionic compounds don't conduct electricity because the ions are not free to move around. When dissolved, ions separate and are free to move so conduct electricity.
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Do covalent compounds conduct electricity?
No. Covalent compounds don't contain ions because they make bonds by sharing electrons. They have no charge carriers that are free to move, so cannot carry an electric current.
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How are metals held together by metallic bonding?
Metals have a giant structure of +ve ions surrounded by a sea of de-localised electrons. The attraction between +ve ions & electrons = metallic bonding.
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Why are metals good conductors of electricity and heat?
Free electrons carry electrical current and heat energy through the material, so metals are good conductors of heat and electricity.
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Why are most metals malleable?
Layers of atoms in a metal can slide over each other, making them malleable. This means they can be hammered or rolled into flat sheets.
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What is electrolysis used for?
To make new substances. If you pass an electric current through an ionic substance that's molten/in solution it breaks down into new substances.
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What is needed for electrolysis?
A liquid to conduct the electricity (ELECTROLYTE). Electrolytes are made by melting/ dissolving ionic compounds- free ions conduct the electricity. Electrons taken away from anode (+ve electrode), given to cathode (-ve electrode).
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What are electrolytes?
Liquids that conduct electricity. Conductivity probe in electrolyte, current flows through circuit (can measure its conductivity). C Probe in non-electrolyte, no current, reading of 0.
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Electrolysis in molten ionic compounds.
Can be electrolysed because ions move freely, usually broken up by elements. +ve ions attracted to -ve cathode. Electrodes are made from an inert (unreactive) material so they don't take part in the reaction.
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Half equation at the cathode.
M^n+ + Ne^- -> M
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Half equation at the cathode.
2X^n- -> x2 + 2ne^-
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Electrolysis of aqueous solutions.
Cathode, H+ ions & metal ions present H2 gas made, if metal ions are more reactive than H+ ions. If metal ions are less reactive than H+ ions, a solid layer of pure metal will be produced instead. Anode, if OH- & halide ions present, halide molecules
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Electrolysis of sulfuric acid (H2SO4)
Cathode: 2H^+ + 2e^- -> H2. Anode: 4OH- -> O2 + 2HO + 4e^-
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Electrolysis of sodium chloride (NaCl)
Cathode: 2H^+ + 2e^- -> H2. Anode: 2Cl^- -> Cl2 + 2e^-
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Electolysis of copper(II) sulphate (CuSO4)
Cathode: Cu^2+ + 2e^- -> Cu. Anode: 4OH^- -> O2 + 2H2O + 4e^-
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Half equation at the cathode if Cu or Ag in an aqueous solution.
M^n+ + ne^- -> M
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Half equation at the cathode if not Cu or Ag in an aqueous solution.
2H^+ + 2e^- -> H2
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Half equation at the anode if a halogen.
2x^n- -> X2 + 2ne^-
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Half equation at the anode if not a halogen.
4OH^- -> 2H2O + O2 + 4e^-
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Number of electrons transferred increases with time and current.
Electrolysing for a longer time, or increasing the current increases the number of electrons transferred.
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Coulombs and Faradays.
1 amp flowing for 1 second = charge of 1 coulomb has moved. Q = I x t. One Farady = one mole. 96000 coulombs = 1 faraday.
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Calculating mass with electrolysis.
Blaanced half-equation for cathode. NUmber of faradays. Number of moles of lead produced. Mr values, to work out mass.
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Card 2

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Describe a liquid.

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Weak force of attraction between particles, randomly arranged and free to move past each other. They tend to stick closely together.

Card 3

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Describe a gases.

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Preview of the front of card 3

Card 4

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Define diffusion.

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Card 5

Front

Experiment to show diffusion with water.

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