Chemistry Paper 1 & 2 Flashcards
Element
substance made up of only 1 atom that all have same no. of protons
2,8,8,2
Compound
Contain 2 or more elements chemically combined
Mixture
Consists of 2 or more elements or compounds not
chemically combined together.
Particles
Protons- mass: 1, charge: +1
Neutrons-mass:1, charge: 0
Electrons- mass: very small, charge: -1
Mixtures can be separated by…
Filtration- separate insoluble solid from liquid.
Crystallization- separate soluble solid from liquid. water will evaporate.
Simple distillation- evaporate the liquid by heating, condense liquid back to a vapor by cooling
Fractional distillation- separate a mixture of different liquids, and they must have different boiling point.
evaporated solvent and collecting
Paper chromatography- different substances have different solubilities.
Isotopes
Same no. of protons, different number of neutrons
John Dalton
Solid sphere, can’t be created/ destroyed. Were arranged in atomic weight.
JJ Thomson
Plum pudding model
Positively charged sphere
Negatively charged electron
Whole atoms is neutral
Rutherford
Alpha particles went straight through gold foil, however some deflected (changed direction), reflected meaning atom wasn’t empty.
-The nucleus is surrounded by negatively charged electrons.
-nucleus is positively charged
-most of the atom was empty space.
-mass concentrated at the centre
Niels Bohr
Electrons exist in shells, at specific distances.
James Chadwick
Nucleus contains of neutrons and protons.
Describe three other differences between the nuclear model of the atom and the plum pudding model.
-in nuclear, the atom is mostly empty space.
-the positive charge is all in the nucleus in nuclear, in the plum pudding model the atom is a ball of positive charge with embedded electrons.
-the mass is concentrated in the nucleus, in the plum pudding model the mass is spread out.
Why is electrons with less shells less reactive?
Outer electrons are closer to nucleus
Greater attraction between nucleus and electrons
More energy needed to remove electrons, more difficult
Groups ( 8 groups)
Rows , eg Li, Na, K.
No. of electrons outer shell
meaning similar chemical properties.
Periods (7 periods)
Columns, eg, Li, Be, B, C
no. of shells
Group names
Group 1- alkali , more reactive as they go down.
Group 2- alkaline
Middle- Transition metals
Group 7- Halogens, less reactive as you go down
Group 8- Noble gases, they are unreactive and do not easily form molecules because they have eight electrons in their outer shell, which are stable.
Metals and Non metals
Metals always form positive ion.
Group 0
Noble gases
Colorless gas! Non flammable.
They are unreactive as they have a full outer energy shell.
The boiling points of the noble gases increase with going down the group, as relative masses increase.
Group 1
Alkali metals and have similar chemical properties, as they have single electron in their outer shell.
Low density, increases when going down.
In Group 1, the reactivity increases going down the group, loses its electron more easily, as its further away from nucleus.
React with water-> produces hydrogen gas, and form hydroxides that dissolve in water to give alkaline solutions
React with chlorine-> produces salt, form white salts, called sodium chloride.
React with oxygen-> metal oxides
Low density, soft
Low melting boiling points. Reactions are vigorous
Group 7
Halogens
Colored vapours,
Fluorine is a very reactive, poisonous yellow gas.
Chlorine is a fairly reactive, poisonous dense green gas.
Bromine is a dense, poisonous, red-brown volatile liquid. lodine is a dark grey crystalline solid or a purple vapour.
In Group 7, the more down you go in group an element is the higher its relative mass (molecules get bigger), melting point and boiling point, increases.
Going down group 7:
the atoms become larger
the outer shell becomes further from the nucleus
the force of attraction between the nucleus and the outer shell decreases
an outer electron is gained less easily
the halogen becomes less reactive
Higher relative mass
flouride, chloride
Oxidation and Reduction equations
Oxidation: Al–> Al3+ +3e-
Reduction: O + 2e- –> O2-
Acids, neutral, Alkaline
Acids- 1-6, red, orange, yellow
Neutral- 7, dark green
Alkaline- 8-14, purple, blue
Ions
Formed when atoms lose (positive ions) or gain electrons (negative ions)
Ionic bonding
Oppositely charged ions
Held by electrostatic forces in a giant lattice.
Metals and non metals
High melting/boiling points
Only conduct electricity when dissolved in water, as ions are free to move.
Ionic compounds
An ionic compound forms giant structures, giant ionic lattice
Ionic compounds are held together by strong electrostatic forces of attraction between oppositely charged ions, high melting and boiling points.
Water, Methane, Ammonia
H20
CH4
NH3
Simple covalent bonding
Share pairs of electrons.
Non metals
Don’t conduct electricity, as no ions.
Weak intermolecular forces , low melting/ boiling point. strong bonds
Metallic bonding
Share delocalised electrons.
Metals.
Strong forces, meaning high melting/boiling points, good conductors as they have delocalised electrons carrying charge
Small molecules
H2
Cl2
O2
Methane
Hydrogen chloride HCl
H2O
N2
Low melting points and boiling points. Need to break force not bond, so easily parted.
These substances have only weak forces between the molecules (intermolecular forces), strong covalent bonds.
Gases and liquids at room temperature.
The intermolecular forces increase with the size of the molecules, so larger molecules have higher melting and boiling points.
These substances do not conduct electricity because the molecules do not have an overall electric charge.
Polymers
Polymers have very large molecules., made by joining of monomers
Single bonded
The atoms in the polymer molecules are linked to other atoms by strong covalent bonds.
The intermolecular forces between polymer molecules are strong and so these substances are solids at room temperature, but weaker than ionic or covalent bonds , lower boiling point than them
Properties of metals and alloys
Metals have giant structures of atoms with strong metallic bonding.
This means that most metals have high melting and boiling points.
In pure metals, atoms are arranged in layers, which allows metals to be bent and shaped.
Layers of atoms are able to slide over each other.
Pure metals are too soft for many uses and so are mixed with other metals to make alloys which are harder.
Alloys is a mixture of metals, the different sizes of atoms distort the layers, making it more difficult to slide over eachother, they are harder than pure metals.
Metal conductors
Metals are good conductors of electricity because the delocalised
electrons in the metal carry electrical charge through the metal.
Metals are good conductors of thermal energy because energy is
transferred by the delocalised electrons.
Giant covalent structures
strong bonds
high melting and boiling points
-diamond, made from carbon
-graphite, made from carbon
- silicon dioxide, silicon and oxygen
Diamond (see pictures)
each carbon atom bonds to 4 other carbon atoms by covalent bonds
Very hard , and melting points (strong bonds)
Don’t conduct electricity, no electrons are free to move
Silicon dioxide
silicon and oxygen
In silicon dioxide, each silicon atom is bonded with 4 oxygen atoms.
has a high melting point, it is a giant structure, strong bonds, a lot of energy needed to break bonds
The word ‘nano’ means the wires are very thin. a layer a few hundred atoms thick
Graphite (see pictures) not a metal as formed by carbon
each carbon atom bonds to 3 other carbon atoms by covalent bonds
High melting point
Layers free slide as weak forces between layers. Soft
Conduct electricity.
contain sheets of hexagons.
Graphene
Single layer of graphite
good conductor
strong
light
high melting and boiling points. Graphene’s many covalent bonds are strong and need energy is needed to break them.
Solid, liquid and gas
Solid-Have strong intermolecular forces holding the particles together. The particles are very close together, stuck in fixed positions but vibrating on the spot.
Liquids-the forces of interaction between particles are weak. The particles are randomly arranged and move slowly past each other.
Gases- no forces of interaction between particles. The particles are randomly arranged and move quickly and randomly with lots of energy
Fullerenes (see pictures)
Hollow shaped molecules
Based on hexagonal rings of carbon atoms but they may also contain rings with 5 or 7 carbon atoms.
Form spheres and tubes.
Buckminsterfullerene C60 (SEE PIC)
First fullerene discovered.
Hollow sphere
6 or 5 carbon rings
Uses are catalysts, huge surface area, great lubricants.
Form nanotubes
Nanotubes (see pictures)
tiny carbon cylinders
Strong bonds
Conducts electricity and thermal energy.
don’t break when stretched
Used in electronics or to strengthen materials without adding too much weight, like tennis racket frames.
In the reaction shown by the equation below, what mass of sulfur dioxide can be made from 16 g of sulfur? (Mr of SO2 = 64)
S(s) + O2(g) → SO2(g)
Amount of S= 16 / 32
= 0.5 mol
The equation shows that 1 mol of sulfur reacts with 1 mol of oxygen molecules to make 1 mol of sulfur dioxide. This means that 0.5 mol of sulfur makes 0.5 mol of sulfur dioxide.
mass of SO2 = relative formula mass × mol
= 64 × 0.5
= 32 g
Moles formula
Mass(g)= No. of moles (mol) x formula mass g/mol
Moles to balance equations
first, find no. of moles, and then divide by the smallest moles in all the atoms, and put in equation.
calculate the amount in moles of oxygen molecules that reacts with 2 mol of magnesium metal.
2Mg(s) + O2(g) → 2MgO(s)
The equation shows that 2 mol of magnesium metal reacts with 1 mol of oxygen molecules.
law of conservation of mass
The law of conservation of mass states that no atoms are lost or
made during a chemical reaction so the mass of the products
equals the mass of the reactants.
Limiting reactant
1) Mass of reactants is less than the mass of the products
- When reactant is gas, the gas will not be part of the unsealed reaction vessel.
The reactant that is completely used up is called the limiting reactant because it limits the amount of products.
Number of atoms
= Avogadro constant × the amount of substance in mol
Calculate the number of water molecules in 0.5 mol of water.
Number of water molecules = Avogadro constant x amount of substance in mol
= 6.02 × 1023 × 0.5
= 3.01 × 1023
Concentration formula
Mass = concentration g/dm3 x volume dm3
1 dm3 = 1000 cm3
Oxidation and Reduction (OIL)
Oxidation is loss of electrons
Reduction is gain of electrons
Acid
hydrochloric acid produces chloride.
nitric acid produces nitrates.
sulfuric acid produces sulfates.
The Ions for Acids
An acid is a substance that forms H+ ions when dissolved in water.
A more acidic solution will have a greater concentration of H+ ions.
As we move down the pH values by 1 for acids, the concentration of H+ ions increases by a factor of 10.
6pH to 4pH —-> 10 x 10
Ions for Bases
When alkalis dissolve in water, they produce OH- ions (negative hydroxide ions)
Measure pH of solution
If universal indicator is added to a solution it changes to a colour that shows the pH of the solution.
it will be green for neutral solutions.
orange/ red for acidic solutions.
blue/ purple for alkaline solutions.
A more accurate value can be obtained using a pH probe. We do this by placing the probe into the solution and looking at the digital screen to see the pH value.
Metals and acids
Metal + acid → salt + hydrogen
Reactions of metals with water
When a metal reacts with water, a metal hydroxide and hydrogen are formed. For example, sodium reacts rapidly with cold water:
Sodium + water → sodium hydroxide + hydrogen
Reactions of metals with dilute acids
When a metal reacts with a dilute
acid, a salt and hydrogen are formed. For example, magnesium reacts rapidly with dilute hydrochloric acid:
Magnesium + hydrochloric acid → magnesium chloride + hydrogen
Platinum will not react with dilute acids. Metals below hydrogen in the reactivity series do not react with dilute acids, and both gold and platinum are placed below hydrogen.
pH of alkaline solutions
The higher the concentration of OH- ions in an alkaline solution, the higher the pH.
A solution of 1 g/dm3 hydrochloric acid has a pH of 1.6. Predict its pH when it is diluted to 0.1 g/dm3.
The hydrogen ion concentration decreases by a factor of 10, so the pH increases by 1 from 1.6 to 2.6.
Neutralisation
Acid + Base—> Salt + Water
H+ + OH- —> H20
The products of a neutralisation reaction are neutral
Metal carbonate and acid
Metal carbonate + acid —> salt + water + carbon dioxide
Metal oxide and acid
Metal oxide + acid —-> salt + water
Bases & Alkali
base+ acid —-> salt + water
Bases neutralise acids.
A base can be a metal oxide or a metal hydroxide.
metal oxides
metal hydroxide
metal carbonate
Alkali is a base
Bases that dissolve in water are also known as alkalis.
A base that is insoluble in water is just a base and not an alkali.
Reactivity series
Potassium
Sodium
Lithium
Calcium
Magnesium
Aluminum
Carbon
Zinc
Iron
Tin
Lead
Hydrogen
Copper
Silver
Gold
Platinum
Ores
compound of metal found in rocks, in Earth’s Crust
Strong and weak acids
A strong acid is completely ionised in aqueous solution. Examples
of strong acids are hydrochloric, nitric and sulfuric acids.
A weak acid is only partially ionised in aqueous solution. Examples
of weak acids are ethanoic, citric and carbonic acids.
More reactive than carbon- electrolysis
Less reactive than carbon- extracted using carbon
Electrolysis
Splitting of substances using electricity.
Passing an electric current through electrolytes causes the ions to move to the electrodes.
Positively charged ions move to the
negative electrode (the cathode), and negatively charged ions move to the positive electrode (the anode).
Ions are discharged at the
electrodes producing elements. This process is called electrolysis.
The metal (lead) is produced at the cathode and the non-metal (bromine) is produced at the
anode.
Electrode
made up of carbon/graphite, electric current passses through it
Suggest why the annual world production of iron is forty times greater than that of aluminium
- cheaper / costs less
- easier to extract
- iron has more uses
- more demand for iron
Why is mixture used as electrolyte?
A mixture is used as the electrolyte because a mixture of positive and negative ions are needed.
The electrolyte is a molten form of the ionic compound or the ionic compound dissolved in water (an aqueous solution).
The electrolyte needs to be molten or an aqueous solution so that the ions in the ionic compound are free to move and conduct electricity.
The electrolyte cannot be a solid ionic compound because the ions in a solid ionic compound are in their fixed positions and are unable to move, which means that they will not conduct electricity.
Water solution
H+ ions are attracted to the cathode, gain electrons and form hydrogen gas
OH- ions are attracted to the anode, lose electrons and form oxygen gas.
4OH- –> O2 + 2H2O + 4e-
the metal is produced at the cathode if it is less reactive than hydrogen.
hydrogen is produced at the cathode if the metal is more reactive than hydrogen
During electrolysis, at the cathode (negative electrode), positively
charged ions gain electrons and so the reactions are reductions.
At the anode (positive electrode), negatively charged ions lose
electrons and so the reactions are oxidations.
Reactions at electrodes can be represented by half equations, for
The electrodes are usually made of graphite, which is a giant covalent structure of carbon atoms. The electrodes are made of graphite because graphite has a very high melting point and is a very good conductor of electricity.
The electrodes are usually made of graphite, which is a giant covalent structure of carbon atoms.
The electrodes are made of graphite because graphite has a very high melting point and is a very good conductor of electricity.
