Chemistry Paper 2: Topics 1 + 6-8 Flashcards
What does aqueous mean
Dissolved in water
What is the chemical formula of: Water Carbon dioxide Chlorine Ammonia Hydrogen
H2O CO2 Cl2 NH3 H2
When is an ion formed
When an atom loses or gains an electron
What are the formulas for these ions made up of groups of atoms: Ammonium Nitrate Sulfate Hydroxide Carbonate
NH4+ NO3- SO4(2-) OH- CO3(2-)
How do you write an ionic equation
Balance the symbol equation. Take out aqueous ions present on both sides. anything and aqueous will break up into its ions in solution, so in equation show all aqueous ions separately. Only the particles that react and are products are included
Describe the history of the Atom
1; solid spheres. Different spheres make different elements
2; measurements of charge and mass, so atom must contain electrons (plum pudding)
3; gold foil experiment. Alpha particles fired at thin gold sheet. Some went through, some deflected, some sent backwards. Nuclear Atom: positively charged nucleus at centre, ‘cloud’ of negative electrons. Rest is empty space
4; Bohr, electrons exist in a fixed orbit, each shell has fixed energy
What is relative mass and relative charge of:
Proton
Neutron
Electron
Proton; relative mass 1, relative charge +1
Neutron; 1, 0
Electron; 0.0005, -1
What’s the atomic radius of most atoms
10^-10m
What does atomic number tell you, what does mass number tell you
Atomic number = how many protons. every atom of an element has same atomic number
Mass number = total number of neutrons + protons in atom. The biggest number in the nuclear symbol is always the mass number
What’s an isotope
Different form of the same element. Same number of protons, different number of neutrons. So same atomic number, different mass number.
What’s the relative atomic mass of an element
The biggest number in the nuclear symbol on a periodic table. So the mass number
How do you work out relative atomic mass of an isotope.
If element only has one isotope, Ar is same as mass number
Element has more than one isotope: Ar of all atoms in an element is average of mass numbers of all the different isotopes, taking into account how much there is of each one
^ multiply each relative atomic mass by its isotopic abundance, add up the results
Divide this number by the sum of abundances (if abundances given as percentages, this will be 100)
Describe the early periodic table
Dmitri Mendeleev made it in 1869. Arranged about 50 elements into ‘table of elements’. Similar properties in columns. Elements ordered by atomic mass.
Describe modern periodic table
Elements are in order of ascending atomic number. Elements with similar chemical properties form groups (columns). Group number = number of electrons in outer shell. Group 0 is the exception; they all have full outer shells, except helium which has 2.
Periods = the rows. Period number corresponds to number of shells
What are: Ions Anions Cations Charge of ion
Ions = charged particles. Can be single atoms or groups of atoms
Anions = negative ions. Form when atoms gain electrons
Cations = positive ions. form when atoms lose electrons
Charge of ions = how many more/less electrons there are than protons
Elements in same group form ions with same charges
What is a stable electronic structure
Full outer shell of electrons. Overall charge of any ionic compound is zero.
What does it mean if ion ends in ‘Ate’ or ‘ide’
‘Ate’ = negative ions containing oxygen and at least 1 other element
‘Ide’ negative ions containing only one element, apart from hydroxide ions which are OH-
What is ionic bonding
When a metal and non metal react together, the metal atom loses electrons to form an anion. These oppositely charged ions are strongly attracted to one another by electrostatic forces. This is an ionic bond.
Describe dot and cross diagrams
Show arrangement of electrons in an atom or ion. Can show which atom an electron in an ion came from
Describe ionic compounds
Always have giant ionic lattice structures. Ions form regular lattice, strong electrostatic forces of attraction between oppositely charged ions in all directions. Throughout the lattice oppositely charged ions will alternate
Describe the properties ionic compounds share
High melting boiling points due to strong attraction between ions
Solid ionic compounds don’t conduct electricity, ions fixed in place
Many dissolve easily in water. Ions separater, free to move in solution
List three models used to show ionic compounds
2D representation (displayed formulas) of molecules Dot and cross diagram 3D models of ionic solids Ball and stick models
What’s a covelant bond
Strong bond that forms when a pair of electrons is shared by two atoms
What are simple molecular substances. What are the common properties of simple molecular substances?
Made up of molecules containing a few atoms joined by covalent bonds. Atoms within molecules held together by strong covalent bonds. Forces of attraction between molecules very weak.
Melting boiling points low (only need to part molecules)
As molecules get bigger, strength of intermolecular forces increases
Don’t conduct electricity: no free electrons or ions
Some are soluble, some aren’t
What is the covalent bonding in the following simple molecular structures: Hydrogen Hydrogen chloride Water Oxygen Methane Carbon dioxide
Hydrogen, 2 hydrogen atoms form single covalent bond
Hydrogen chloride, single covalent bond between H+Cl atoms
Water, single covalent bonds between H+H+O
Oxygen, O+O double covalent bond
Methane, C+H+H+H+H, 4 covalent bonds
Carbon dioxide, O+C+O, 2 double covalent bonds
What’s a double covalent bond
A bond made of 2 shared electron pairs
What are polymers, what are monomers
Polymers are molecules made of long chains of covalently bonded carbon atoms, formed when many monomers join together
Monomers = lots of small molecules
What are the similar properties of most giant covalent structures
All atoms bonded together by strong covalent bonds
Very high melting boiling points
Generally don’t contain charged particles, so don’t conduct electricity (except graphite and graphene)
Aren’t soluble in water
Describe the structure of carbon based giant covalent structures
Diamond: network of carbon atoms, each form 4 covalent bonds. High melting point, atoms held in rigid lattice structure. Doesn’t conduct electricity. Strengthens cutting tools.
Graphite: each carbon atom forms 3 covalent bond, creating sheets of carbon atoms arranged in hexagons. No covalent bonds between layers, so they’re free to move over each other. High melting boiling point due to covalent bonds. Each carbon has 1 delocalised electron, can conduct electricity
Graphene: type of fullerene. 1 layer of graphite. Sheet 1 atom thick.
What are fullerenes
Molecules of carbon shaped like closed tubes or hollow balls. Made of carbon atoms arranged into hexagons. Can be used to cage other molecules. Have huge surface area.
Describe two examples of fullerenes
Buckminster fullerenes, C60: forms hollow sphere of 20 hexagons and 12 pentagons. Stable molecule. Forms soft black crystals.
Nanotubes: tiny cylinders of graphene. Conduct electricity. High tensile strength (doesn’t break when stretched)
What’s metallic bonding
Metals consist of a giant structure. Electrons in outer shell of metal atoms are delocalised. Strong forces of attraction between positive metal ions and shared negative electrons. These forces hold atoms together in regular structure. This is metallic bonding.
Metallic elements and alloys are compounds held together by metallic bonding.
What are the similar properties for compounds held together by metallic bonding
All properties come from the delocalised electrons
High melting boiling points. Usually shiny at room temperature. Not soluble in water. Denser than non metals, as ions in metallic structure are packed closely. Pure metal is malleable as layers of atoms can slide over each other. Delocalised electrons carry electrical current + thermal energy through material. Usually lose electrons to gain full outer shell.
What’s relative formula mass (Mr)
Relative atomic masses of all atoms in a compounds formula added together. Mr of compound is equal to mass in grams of 1 mole of the compound
What’s empirical formula
Smallest whole number ratio of atoms in the compound
How can you work out the molecular formula of a compound
Use empirical formula and Mr (relative formula mass). Find Mr of compound. Divide Mr of compound by Mr of empirical formula.
Molecular formula = everything in empirical formula x result
What is a mole
An amount of particles equal to Avagadros constant, 6.02 x 10^23
One mole of atoms or molecules of any substance will have a mass in grams equal to the Ar or Mr for that substance
What’s the equation for number of particles
Number of particles = number of moles x avagadros constant
What’s the equation to find number of moles in a certain mass of something
Number of moles = mass in g (of element or compound) / Mr (of compound) OR Ar (of element).
What’s a solute
The solid you’re dissolving
What’s equation for concentration of a solution
Concentration (g/dm^-3) = mass of solute (g) / volume of solution (dm^3)
How do you calculate empirical formula of compounds
Use the masses of elements the compound contains. Work out how many moles of each element there are, work out the smallest whole number ratio between the moles of all elements/ atoms to get the empirical formula
This is the heating crucible to calculate EF of a metal oxide eg magnesium oxide experiment
What is the limiting reactant in a reaction
The reactant that gets completely used up
How do you calculate amount of product formed from the limiting reactant
Write balanced equation
Work out MR of reactant and product interested in
Find out how many moles there are in substance you know the mass of
Use balanced equation, work out how many moles of the other substance there will be
Use number of moles to calculate mass
How do you work out balanced symbol equation using masses of reactants and products
Divide mass of each substance by its relative formula mass to find the number of moles
Divide no of moles of each substance by smallest number of moles in the reaction
If needed, multiply all numbers by same amount to make them all integers
Write balanced symbol equation for reaction by putting these numbers in front of the formulas
What are halogen displacement reactions
Halogens, taking part in displacement reactions. They are redox reactions for halogens as the halogens gain electrons (reduction) and the halide ions lose electrons (oxidation)
Equations for halogen displacement reactions follow the pattern:
Cl2 + 2KBr > Br2 + 2KCl
How do you use displacement reactions to show reactivity trends of halogens
Measure small amount of Halide salt solution into a test tube
Add couple drops of halogen solution, gently shake test tube
If see colour change, reactions happened - halogen has displaced halide ions from the salt. If theres no change, haolgen is less reactive than halide, so no reaction
Repeat using different combinations. Should conclude halogens get less reactive as go down the group
What are the properties of the elements in Group 0
Noble gases;
All colourless gas at room temp, all monatomic (made of single atoms), all mostly inert because all have full outer shell electrons. All non flammable.
Used to provide inert atmospheres. Boiling point, melting point and density increase as go down group 0
What are the properties of the elements in Group 1
Alkali metals:
All have 1 outer electron. All have low mbp, very soft. Alkali metals form ionic compounds, lose electrons easily. Form a 1+ ion with a stable electronic structure. Very reactive.
As go down group 1, atomic radius larger, metal more reactive.
How do the alkali metals behave with water
React vigorously in water. Reaction produces hydrogen gas and a hydroxide of the metal.
More reactive metal has a more violent reaction with water.
What are the similar proprieties of the elements in group 7
Halogens
All have 7 electrons in outer shell. Halogens are diatomic molecules (travel in pairs), sharing 1 pair of electrons in a covalent bond, so both atoms have a full outer shell
As go down group 7 melting and boiling points increase
At room temp: chlorine is a fairly reactive, poisonous green gas. Bromine is a poisonous, red brown liquid, gives off an orange vapour. Iodine is a dark grey crystalline solid, gives off purple vapour when its heated.
Reactivity decreases down group 7.
How do you test for chlorine
Hold damp blue litmus paper over it. Chlorine turns it red for a moment as solution of chlorine is acidic, then bleaches it white
What are halogen halides
Halogens react vigorously with some metals to form salts called metal halides. Can also react with hydrogen to form hydrogen halides. Hydrogen halides are soluble, dissolve in water to form acidic solutions. Halides all have similar reactions
Equation for rate of reaction
Rate of reaction = amount of products used OR amount of product formed / time
Describe a precipitation experiment to follow reaction rate and how its affected by temperature
Works for reaction where mixing 2 see through solutions form a precipitate, which clouds the solution
Mix 2 reactant solutions, put flask on paper with a mark on it. Observe mark through mixture, time hope long it takes for mark to be obscured. Faster it disappears means faster rate of reaction.
Use fixed volumes of sodium thiosulfate and hydrochloric acid. Gently heat both to desired temperature. Mix, do the precipitation reaction. Repeat and change temp each time. Increased temp = faster reaction
Describe a Change in mass experiment to follow reaction rate
Measures rate of reaction that produces gas
As gas released, lost mass measured on mass balance. Quicker reading on balance drops means faster reaction. Reaction done when balance stops changing. Use results to plot graph of change in mass against time
Describe a volume of gas given off experiment to follow reaction rate
Use gas syringe to measure volume of gas given off. More gas given off during set time interval means faster reaction. Can tell reaction finished when no more gas is produced. Use results to plot graph of gas volume against time elapsed. Use right size gas syringe to avoid damaging it
How would you measure effect of surface area on rate, using marble chips and hydrochloric acid
Measure volume of gas produced using gas syringe, take readings at regular time intervals. Repeat experiment but have marble chips more crunched up each time, until you’re using marble chalk powder. Using finer particles means a larger surface area, meaning faster rate of reaction.
On a graph of amount of product formed or used against time, what does the following tell you:
Gradient
A steeper slope
Gradient = rate of reaction
Steeper slope = faster rate of reaction
Use a tangent to find the gradient
What does rate of reaction depend on
Temperature, concentration, pressure (for gases), size of particles (for solids)
What’s a successful collision
Collision ends in particles reacting to form products
How does particle collisions affect rate of a reaction
Rate depends on frequency of reacting particles colliding and the energy transferred during this collision. Increasing number of collisions increases rate of reaction
What’s activation energy
The minimum energy particle needs to react upon collision. Minimum energy needed for bonds to break and reaction to start
How does temperature affect rate of reaction
Increased temperature > increased rate
Temperature increases means particles move faster, meaning more collisions. High temperature means increased energy of collisions, meaning there are more successful collisions, meaning theirs an increased rate
How do pressure and concentration affect rate of reaction
Increased pressure or concentration increases the rate
If a solution is more concentrated, there are more particles of reactant in the same volume, meaning collisions are more likely, so the rate is increased
If a gas is increased in pressure the particles are more crowded, so the frequency of collisions between particles is increased, so rate is increased
How does surface area affect rate
Higher surface area means higher rate. A solid reactant is broken into smaller pieces, so has an increased surface area to volume ratio. Greater area exposed to particles around reactant, so frequency of collisions increases, meaning theres an increased rate
How do catalysts affect rate of reaction
They increase it, without being chemically altered themselves. Using a catalyst decreases the activation energy needed for the reaction to occur. They provide an alternate reaction pathway that has a lower activation energy, meaning more particles have the minimum activation energy required for reaction when the particles collide
What does endothermic mean. What does exoteric mean
Exothermic = reaction gives out energy to surroundings Endothermic = reaction takes in energy from surroundings
What are reaction profiles
They show energy levels of reactants and products in a reaction.
For the exothermic reaction profile, Difference in height represents energy given out in reaction. For the endothermic reaction profile, it represents energy taken in during the reaction
If energy input is less than activation energy, nothing will happen
How do you follow the change of temperature of a reaction mixture during a reaction
Put polystyrene cup in large beaker of cotton wool (insulating), add known volume of first regent to cup. Measure initial temperature. Add second regent, stir. Put lid on cup. Record max or min temp of mixture during reaction, calculate temperature change,].
Are the following reactions endo or exotehrmic Dissolving salts in water Neutralisation reactions Displacement reactions Precipitation reactions
Dissolving salts in water; endo or exothermic
Neutralisation reactions; an acid or base react to form a salt and water. Most exothermic. However, ethanoic acid and sodium carbonate reaction is endothermic
Displacement reactions; more reactive element displaces less reactive element in compound. Always exothermic
Precipitation reactions; always exothermic
With bonds breaking and bonds forming during a reaction, which is exotehrmic and which is endothermic
Bonds breaking is endothermic, bonds forming is exothermic
What’s bond energy
The particular energy associated with every chemical bond
Equation for overall energy change of a reaction
Overall energy change = energy required to break bonds - energy released by forming bonds
What’s crude oil
The main source of hydrocarbons. Used as a feedstock (raw material) to create substances used in petrochemical industry. Its non renewable, firmed at high temps and pressures from remains of plants and animals over millions of years.
It is a complex mixture of hydrocarbons. They have their carbon atoms arranged in chains or rings and are mostly alkanes
What’s an alkane
Hydrocarbons with the general formula CnH2n+2. A type of hydrocarbon that is saturated (cant absorb anymore hydrogen) Molecular formula (number of atoms in 1 molecule) is CH4, with the carbon covalently bonded to the four hydrogens
What’s a hydrocarbon
A compound containing just hydrogen and carbon
What are fractions
Simpler, more useful mixtures containing groups of hydrocarbons of similar lengths (number of atoms)
Fractions of crude oil are non renewable fossil fuels.
What’s fractional distillation
Process used to separate fractions in crude oil. Oil is heated until mostly gas, which enters fractionating column. Bitumen remains liquid, is drained off at bottom. Column has a temperature gradient: hot at bottom, cooler as go up. Longer hydrocarbons have higher boiling points, so drain out of column near the bottom as they condense early on.
What are the fractions of crude oil
Each fraction of crude oil contains a mixture of hydrocarbons, mostly alkanes, with similar boiling points. Physical properties of fraction depends on size of hydrocarbons in the fraction
(Least hot part of fractionating column)
Gases, approx 3 carbons, used for domestic heating and cooking
Petrol, approx 8, fuel in cars
Kerosene (paraffin), approx 15, fuel in aircrafts
Diesel oil, approx 20, fuel in cars + larger vehicles
Fuel oil, approx 40, fuel in ships + power stations
Bitumen, approx 70+, surface roads and roofs
(Very hot part of fractionating column)
What’s volatility
How quickly a substance evaporates
What’s a homologous series
A family of molecules sharing the same general formula and similar chemical properties. Molecular formulas of neighbouring con pounds in a homologous series differ by a CH2 unit.
Alkanes and alkenes are two different homologous series of hydrocarbons
What’s viscosity
Measure of how easily a substance flows
How do hydrocarbons and molecule size affect viscosity, flammability, boiling point
Small molecule means lower boiling point
Shorter hydrocarbons means lower boiling point. Easy to ignite, often gas at room temperature. This gas mixes with oxygen, creating gas mixture that will ignite if it comes into contact with a spark.
Shorter hydrocarbons means weaker force between molecules, meaning low viscosity
What’s complete combustion
A combustion reaction with a hydrocarbon, burning hydrocarbon in oxygen. Releases lots of energy, very exothermic. Produces carbon dioxide and water
What’s incomplete combustion
Produces CO2, H2O, carbon monoxide (CO) a Toxic gas, carbon in the form of soot
Why is carbon monoxide dangerous
It combines with red blood cells, stopping blood from carrying oxygen around the body. Lack of oxygen to brain causes death
When fossil fuels are burnt what is produced
CO2, sulphur dioxide SO2, nitrogen oxides
Sulphur dioxide; is from sulphur impurities in fossil fuels. Mixes with clouds, forming dilute hydrochloric acid, acid rain.
Nitrogen oxide; created from reaction between nitrogen and oxygen in air, caused by energy released in a combustion reaction. Nitrogen oxides cause harmful pollutants, contribute to acid rain and cause photochemical smog (type of air pollution, causes tiredness and breathing difficulties)
What’s an Alkene
Unsaturated hydrocarbon. Two carbons double bonded to each other. 1 carbon has 2 covalent bonds to 2 hydrogen. Not enough hydrogen to make it an alkane
What’s cracking
Turns long saturated (alkane) molecules into smaller unsaturated (alkene) and alkane molecules, which are more useful.
It is a form of thermal decomposition; when 1 substance breaks down into at least 2 ones when you heat it. This involves breaking strong covalent bonds, so needs lots of energy. Catalyst often added.
Describe the process of cracking
Vaporised hydrocarbons are passed over powdered catalyst, which is aluminium oxide. The long chain molecules split apart on surface of catalyst
How do scientists get evidence for theories on the early atmosphere
Lok at evidence from rocks, air bubbles in ice and fossils
Describe how the atmosphere is said to have changed
Phase 1, first billion years: volcanoes gave out steam and CO2. Surface molten, no atmosphere. Surface cools, think crust forms. Volcanoes release gas from inside earth, mainly carbon dioxide, also steam, methane and ammonia. Surface settles, early atmosphere mostly CO2 and water vapour, which then condenses to form oceans. Little oxygen.
Phases 2, next two billion years: green plants evolve to produce oxygen. Early CO2 evolves into oceans. Nitrogen gas formed by ammonia reacting with oxygen + released by denitrifying bacteria. Green plants evolve, photosynthesise. Release O2, remove CO2
Phase 3, last billion years: ozone layer allows evolution of complex animals. Build up of oxygen kills many organisms, allowed for evolution of complex, oxygen using organisms. Oxygen creates ozone layer (O3), blocks harmful rays from sun
Explain greenhouse effect
Sun gives out electromagnetic radiation. Most wavelengths pass through the atmosphere, short wavelengths are absorbed by Earth.
Earth radiates some of the heat radiation out absorbs as longer wavelength infrared radiation. Some infrared radiation absorbed by greenhouse gases.
Some IR reflected back to earth by greenhouse gases.
Some IR re-emitted back into space.
The absorption and reflection of IR by greenhouse gases is what causes the greenhouse effect
What are greenhouse gases, what happens if the concentration of them increases
The gases in atmosphere that can absorb and reflect heat radiation. They’re only present in small amounts
Carbon dioxide, water vapour, methane
Concentration of greenhouse gases in atmosphere increases > enhanced greenhouse effect. More heat radiation from earth is absorbed, less re-emitted into space
Why is methane levels increasing
Due to increased human activities. Its produced by the digestive process of certain livestock and humans are farming more
What’s global warming
The scientific consensus that extra greenhouse gases from human activity have caused average temperature of earth to increase, due to enhanced greenhouse effect
Global warming is a type if climate change that causes other types of climate change.
What does anthropogenic mean
Caused by humans
