Chemistry Flashcards
atomic number
number of protons in the nucleus
number at the bottom
mass number
number of protons + neutrons
number at the top of element
relative atomic mass
wighted mean of the mass numbers of isotopes of an element
atomic mass = (abundance x mass)+(abundance x mass) divided by 100
group one elements
alkali metals
one electron in outer shell
group 2 elements
alkaline earth metals
group 17 elements
group 7
halogen
group 18 elements
noble gases
reaction of group 1 elements with water
lithium - reacts slowly with cold water. floats, but does not melt, gradually dissolves to produce and alkaline solution of lithium hydroxide. hydrogen gas is given off, burns with a crimson red flame when ignited
sodium - reacts more strongly with cold water. moves on the surface, melts and quickly dissolves to produce an alkaline solution of sodium hyrdoxide. hydrogen gas is given off and burns with a yellow-orange flame
potassium - reacts vigourusly with water. moves rapidly on the surface, quickly dissolves to produce an alkaline solution of postassium hydroxide. hydrogen gas given off and self ignites to burn with a lilac flame.
avogrado constant
gives the number of particles in 1 mole of a substance
6.022 x 10^23
moles equation
moles = mass (g)/ molar mass (Mr)
percentage composition of a compound
% element= Ar x number of atoms of element in formula of compound/ Mr of compound x 100
gas volume
at RTP, volume of 1 mole of a gas is 24dm^3
moles of a gas = volume/ molar volume (24)
concentration equation
mass of solute (g) / volume of solution (dm^3)
redox
oxidation is loss of electrons
reduction is gain of electrons
redox in covalent compounds
degree of sharing can change
eg in 02 and H2, the bonding electrons are equally shared between the two atoms, but in H2O oxygen has a freater share of the bonding electrons
oxygen has gained an increased share in the bonding electrons so can be thought of as reduction. hydrogen has a lesser share in the bonding electrons so can be seen as oxifation.
oxidation states
oxidation state of an atom in its elemental state is 0
oxidation state of a monatomic ion is equal to the charge on the ion
sum of all oxidation numbers in a compound is 0
sum of oxidation numbers of all th atoms in a polyatomic ion is equal to the charge on the ion
oxidation number or oxygen is always -2, excpet in peroxides (-1), or when combined with fluorine (+2)
oxidation number of hydrogen is +1, except when part of a metal hydride (-1)
disproportionation reacting
a single species is both oxidised and reduced
oxidising and reducing agents
oxidising agents give oxygen to another substance. or oxidisin agents take electrons form another species and is itself rduced
reducing agents remove oxygen from another substance. or reducing agents give up electrons to another species, being itself oxidised
pure substance
contains only a single element or compound
ammonium ion
NH4+
nitrate ion
NO3-
sulphate ion
(SO4)2-
carbonate ion
(CO3)2-
phosphate ion
(PO4)3-
physical properties of group 1 elements
melting and boiling points - low for metals and decrease down the group
densities - low for metals, generally increase down the group
hardness -soft and become softer down the group
conductivity - good conductors of heat and electricity
melting and boiling pint of group one metals
decreases as you go down because the distance of the delocalised electrons from the 1+ centre increases, causing a decrease in metallic bond strengtg
chemical properties of gorup 1 metals
very reactive, stored in oil to prevent them from reacting with oxygen and water in the air
when freshly cut and exposed to air the shiny metals quickly react with oxygen and tarnish, forming the metal oxide
alkali metals react with non metal compounds to form ionic compounds
as group one descends elements become more reactive
trends of group1 metals
as you descend, the alkali metals become more reactive as less energy is reuqired to remove an electron from the atoms of the element.
atomic radius of the elements increase as you go down the group.
distance of outermost electron from nucleus increases
attraction between nucleus and out electron decreases
physical properties of group 17
non-metals with coloured vapours
low melting and boiling points, increase down the group. increase due to increase of intermolecular forces between the molecules due to increasing number of electrons
poor conductors of heat and electricity
fluorine
pale yellow gas
chlorine
yellow-green gas
bromine
red-brown volatile liuid with orange vapour
iodine
grey shiny solid, gives a purple vapour when heated
chmical properties of group 17
reacting by gaining an electron
react wuth metals to form ionic compounds, or with non metals to form covalent compounds
reactivity decreases down the group
a more reactive halogen will displace a less reactive halogen from solutions of its salts
physical properties of group 18
all colourless gasses at room temp and pressure
v
ery low melting and boiling points, increase down the group due to increasing intermolecular forces between atoms due to increasin size of noble gas atoms
densities increase down the group
chemical properties of group 18
noble gases have a complete outer shell of electrons so are very unreactive
exist and single atoms (monatomic)
displacment (separation)
a displacment reaction or a redox reaction can be used to extract an element from a compound
eg, magnesium + copper sulphate solution.
more reactive magnesium acts as a reducing agent and the dissolved copper ions are reduced to solid copper metal. magnesiun is oxidised and ions dissolve in the solution
copper can be removed by filtration
electrolysis
breakdown of an ionic compound using electricity . for electrolysis to occur, the ions need to be mobile - dissolving it in water or melting it
mixture containing mobile ions = electrolyte
a direct current is then applied through the electrolyte using two electrodes
positive ions are attracted to the negative electrode (cathodr)
Negative ions are attracted to the positive cathode (anode)
reduction occurs at the cathode and oxidation at the anode
electrolysis of molten binary ionic compounds
in molten electrolytes, the cation and anion of the compound are discharged. eh in sodium chloride will produce sodium at the cathode and chlorine at the anode.
sodium and chlorine are reactive element so inert unreactive electrodes are used
decanting
separate a solid and a liuid or solution
if the mixture is left, the solid will settle to the bottom of the container, then you can pour away the liquid without disturbing the solid
filtration
used to separate a liuid from an insoluble solid
solid particles are larger and are trapped by the mesh of the filter paper. smaller liquid particles are able to pass through the filter paper into the collection vessel.
separated liquid = filtrate
residue= solid
separating funnel
used to separate two inmiscible liquids
when added, they form two layers. the upper layer has a lower density. the tap is opened and the lower layer can be poured out
distillation
used to separate two substances with different boiling points eg separate the solvent from the solution
mixture is heated to above the boiling point of the solvent. the solvent becomes a vapour and starts to spread. it hits the condenser and cools and condenses to droplets which run down the condenser into the collection vessel.
the higher boiling point solute remains in the heated flask
fractional distillation
used to separate miscible liquids from a mixture. reuires each liquid to have a different boiling point.
mixture is heated, reaches temp of the first boiling point and this first component boils, rises uf the fractioning column towards the condenser where it is condensed and collected.
once first component has boiled away, the remaining mixture is heated more until the boiling point of the next component is reached.
thermometer is used to monitor the temp of the vapour
being condensed
evaporation and crystallisation
used to separate the solvent from a solute
solute is collected not the solvent, so no condensor is used to collect it solvent.
the solution is heated gently until crystals begin to appear. the remaining concentrated solution is then left to evaporate.
dont heat to dryness as some solids may decompose if heated too strongly
chromatography
used to separate mixtures of different solutes, eg dyes in ink, or separate mixture of different liquids
differences in relative affinity to the stationary phase of the chromatogram to the mobile phase (the solvent) lead to the separation of the substances
in paper chromatography, small sample of the mixture is spotted to a piece of chromatography paper. then placed in a beaker which contains a solvent at the bottom. solvent then rises up the paper by capillary action and through the mixture. the different components each have a differen tendency to absorb to the paper. if the component absorbs more readily to the paper then it does not travel up as far.
an Rf value is calculated (retention factor)
Rf = distance travelled by sample / distance travelled by solvent
centrifugation
used to separate hetergenous mixtures based on their differences in partivle mass. generally used to separate solids from liquids
if a liquid is mixed with a solid the solid particles settle to the bottom of a container as the are more dense that the liquid. when the solid is small, random motion and collision of the particles cause them to settle much more slowly and in some cases they dont settle.
centrifugation encourages settling by spinning the mixture at high speed in a horizontal circle. the heavier particles are brought to the end of the tube and settle out first, becoming a pellet at the bottom of the tube.
remaining liquid may be pure or contain small solid particles. the remainder (supernatant) may be decanted into a new tube and spun again at a higher speed to separate the smaller particles.
used in medicine for the separation of blood components such as red blood cells and platelets.
acid
a substance which has the ability to donate H+ ions
when disolved in water will form H+ ions
salt
general name for a compound formed when the hydrogen ions in an acid are replaced by metal ions or other cations
metal + acid
metal + acid = salt +hydrogen
will only occur if metal is more reactive than hydrogen, eg iron will react with dilute acids but gold will not
metal carbonate + acid
metal carbonate + acid = salt + water + carbon dioxide
metal hydroxide + acid
metal hydroxide + acid = salt + water
neutralisation reactions
metal oxide + acid
metal oxide + acid = salt + water
neutralisation reaction
strong acid
undergoes full dissociation in water forming its constituent ions
eg HCl, H2SO4, HNO3
weak acid
only slightly dissociates into its constituent ions in solution
eg carboxcylic acids
concentration of acids
refers to the moles to volume of the solutions of acids
2 mol/ dm3 is considered dilute
6 mol dm3 is considered concentrated
oxides of non metals
some non metal oxides react with water to produce acidic solutiosn
eg sulfuer oxide + water =H2SO3
2NO2+H2) = HNO3 +HNO2
CO2+ H2O = H2CO3
pH
measure of ion concentration in aqueous solution
the higher the concentration of H+ ions, the lower the pH value
a change of 1 on the pH scale corresponds to a change by a factor of 10 in H+ ion concentration
monoprotic, diprotic, tripotic
one mole of an acid substance may be able to form or donate more than one mole of H+ ions into an aqueus solution
monopotic - only able to donate one
strong base
undergoes full dissociation in water forming its constituent ions
sodium hyrdoxide, potassium hydroxise
weak base
only partially forms ions in solution
ammonia
metal oxides and metal hydroxides
some metal hydroxides dissolve in water to form alkaline solutions, releasing OH- ions
Some metal oxides react with water to produce OH- ions and therefore alkaline solutions
wg Na2O + H20 = 2Na+ + 2OH-
neutralisation reaction
when an acid reacts with a base
H+ +OH- = H2O
exothermic normally
bind energies
measure of the average bonf strength of a particular covalent bond
bond energies are measured in compounds in gaseous states and only apply when all reactants and products are in their gaseous state
when a bond is broken, the electrostatic attraction between the atoms needs to be overcome which requires energy, so all bond energies are endothermic.
bond making is exothermic
enthalpy change = bonds broken - bonds made
electrolysis
molten ionic substance or a solution or solution containing ions (electrolyte) is decomposed by an electric current
electrical cell with two inert electrodes (conductors, often made of graphite), immersed into a beaker with the electrolyte.
power supply is DC so that the current passes in one direction only. power supply acts as an electron pump. electrons flow through the external circuit and enter the electrolytic cell via the cathode, which hains a negative charge and is the negative electrode. electrons leave the electrolytic cell via the anode, which then has a positive charge so is the positive elctrode
electrons flow from the positive electrode to the negative electrode
during electrolysis
positive ions ( cations) are attracred the the cathode (negative electrode). Here they gain electrons and are reduced to form neutral atoms/molecules.
negative ions (anions) are attracted to the anode (positive electrode), where they lose electrons and are oxidised to form nuertral atoms/ molecules
electroplating
uses electrolysis to coat a cheap metal with a more expensive one or for protection
eg an obkect that needs to be silver plated is made the cathode ( negative electrode) to attract and reduce the positive metal ions
the anode can be silver, and the silver atoms are oxidised to form silver ions. at the cathode the silver ions gain an electron forming silver atoms which are plated to the object
anode:
Ag = Ag+ + e-
cathode
Ag+ +e- = Ag
purification of copper
small piece of pure copper is chosen as cathode
anode - impure copper
cathode - pure copper
the anode and electrolyte supply the copper ions for electrolysis
at the anode, copper atoms lose electrons to form copper 2 ions
at the cathode copper ions gain electrons to form copper atoms which are plated onto the oure copper electrode
catalytic cracking
second stage in the refining process
allows the production of shorter chain molecules
longer chain molecules are passed over a heated catalyst and are broken down into shorter chain molecules.
this produces smaller hydrocarbond with some double bonds
condensation polymerisation
smaller molecules join together to produce a longer chain molecile, but also produces a small molecul, typically water
condensation polymerisaion involves two different types of monomer molecules
polyesters
condensation polymers in which the monomers are joined by ester linkages
the carboxyl group of a carboxylic acid combines with a hydroxyl group of an alcohol
when these two functional groups react a molecule of water is eliminates and the two cabons are linked by an oxygen
polyamides
condensation polymers in which the monomers are joined by amide linkages
the carboxyl group of a carboxylic acid combines with an amine group (NH2)
proteins
formed from long chains of amino acids joined by amide linkages (peptide bonds)
these long chains are then folded into a particular shape to make a protein
amino acids are a group of organic molecules that consist of an amino group (NH2) and a carboxyl group (COOH), and an R group that is unique to each amino acid
these 3 groups are bonded to the same central carbon atom. the 4th bond is a c-h bond
sodium plus ethanol
slow reaction, produces hydrogen gas and a colourles solution of sodium ethoxide, which is a strong alkali when aqueous
carboxylic acud and alcohol
react to produce an ester, and a water molecule is eliminated
requires an acid catalyst
extracting metals
extracting metals from its ore depends on its position in the reactivity series
often the metal is combined with oxygen.
the most reactive metals form the most stable compounds and will require more energy to extract
metals less reactive than carbon can be extracted using carbon or carbon monoxide
metals above carbon in the reactivity series cannot be and must be extracted using electroylsis. electricity is used to break down the molten ionic compound into its constituent ions
hydrogen test
explodes with a squeaky pop when a burning splint is held at the open end of a test tube
oxygen test
relights a glowing splint
carbon dioxide test
limewater turns cloudy when shaken with the gas
chlorine test
damp blue litmus paper turns red and then is bleached
carbonate ion test
CO3(2-)
react with acid to release carbon dioxide gas
effervescence is observes
can be confirmed as carbon dioxide with limewater
solution of a carbonate will be alkaline
halide ion test
any other ions must be removed first
add dilute nitic acid and the some silver nitrate solution
halide ions will then precipitate as silver halides
silver iodide = yellow
silver bromide = cream
silver chloride = white
sulphate ion test
add dilute nitric acid to remove hydroxide or carbonate ions
then add barium chloride or nitrate. a white precipitate of barium sulphate will form
order of anion tests
carbonates
sulfate
halide
lithium flame test
crimson red
sodium flame test
yellow / orange
potassium flame test
lilac
calcium flame test
red / orange
copper flame test
green
testing using sodium hydroxide
group 1 metal hydroxides are soluble in water
group 2 metal hydroxides are slightly soluble, becoming more soluble down the group
if sodium hydroxide in added to a solution containing a metal ion with a concentration of more than 0.1 mol/dm3 that is not from group 1, then precipitation will occur.
coloured precipitates are formed from transition metals, white precipitates from other metals
copper - blue
fe 2+ - green
Fe 3+ - brown
testing for water
can be identified using solid copper (II) sulfate CuSO4
solid is white when anhydrous but blue when hydrated
a few drops of water on anhydrous copper sulfate will produce a colour change from white to blue
sulfur dioxide
most fuels contain some sulfur dioxide impurities
sulfur dioxide is posionous, colourless, acidic gas with a choking smell
reacts with water and oxygen in the atmosphere to produce sulfuric acid - acid rain
oxides of nitrogen
at high temp and pressures nitorgen in the air can react with oxygen the give nitrogen oxides.
they react with oxygen in water to generste nitric acid - acid rain
