Flashcards in chemistry definitions Deck (65):
isotopes are different atomic forms of the same element, which have the same number of protons but different numbers of neutrons
simplest formula that tells you the ratio of different elements in the compound
tells you the actual number of atoms of each element in a single molecule
6.023 x 10^23
one mole of anything weighs
exactly the Ar of Mr of an element- Ar of C= 12 so one mole of carbon weighs exactly 12g
nitrogen gas- N2 Mr of 2 x 14 = 28 so one mole of N2 weighs exactly 28g
all contain the same number of aprticles
number of moles=
mass in g/Mr
what do solid salts consist of?
a lattice of positive and negative ions
how do you calculate how much water of crysallisation a salt contains?
1) work out the mass of the hydrated salt and the anhydrous salt- using info
2) calculate the number of moles of water lost= difference between mass of hydrated salt and anhydrous salt/ 18(Mr) of water
3) calculate the number of moles of anhydrous salt made- find molar mass and divide mass at beginning by Mr
4) work out the ratio of mo;es of anhydrous salt to moles of water- moles of water/ moles of salt = moles of water
5) X must be a whole number so round the result
what is concentration?
the amount of stuff per unit volume-measured in moles per dm^3
1 moles of substance in 1 dm^3 has a conc of 1 mol/dm^3
no. of moles/volume
no. of moles of a solution=
concentration x volume
how do you convert mol/dm^3 to gram/dm^3?
1) work out the relative formula mass of the chemical (Mr) 2)mass = moles x Mr = so moles in conc x relative Mr= g/dm^3
what do electrons and ions act as?
what is the electric current?
the flow of electrons or ions
why don't solids ionic compounds conduct electricity?
because the ions aren't free to move but when dissolved the ions separate and are free to move in the solution so canny carry electric current and conduct electricity
how are metals held together?
by metallic bonding
- they have a giant structure of positive ions surrounded by a sea of delocalised electrons
- the attraction between the positive ions and the electrons is called metallic bonding
why are metals good conductors of heat and electricity?>
the free electrons carry electrical current and heat energy through the material
why are metals malleable?
the layers of atoms can slide over each other so can be hammered or rolled into flat sheets
what are metal oxides?
basic- neutralise acids- will dissolve to form solutions with a pH of 7 or more
what are non-metal oxides?
acidic- dissolve in water to form a solution with pH of less than 7
what do sodium, lithium and potassium react with water to make?
a metal hydroxide and hydrogen
what is a displacement reaction?
where the more reactive element displaces a less reactive element from a compound
what is an oxidising agent?
accepts electrons and gets reduced
what is a reducing agent?
donates electrons and gets oxidised
loss of electrons=
gain of electrons=
metal + water->
metal hydroxide + hydrogen
mnemonic for reactivity series
(Hot ) HYDROGEN
iron corrodes to make?
rust iron(lll) oxide
iron + oxygen + water-->
hydrated iron (lll) oxide (rust)
what are the 2 main ways of preventing rust?
1) BARRIER METHODS
- painting/coating with plastic- good for big and small structures
-oiling/ greasing- moving parts like bike chains
2) SACRIFICIAL METHOD
- placing a more reactive metal with the iron- zinc- will be oxidised instead of iron
- a coat of zinc can be sprayed onto the object- galvanising
- big blocks of zinc can be bolted to the iron
how can you investigate the proportion of O2 in the air?
1)using copper- when heated reacts with air-> copper (ll) oxide
-heat excess copper in a tube and air passes over using 2 syringes, once copper is black measure how much air is there- if started with 100cm^3 then about 20cm^3 will have been used up so around 20% of the air must be oxygen
2) using iron or phosphorus
-put iron filings or iron wool in test tube inverted into beaker of water
- measure vol of water at start
- measure vol of water at the end
-use difference in vols to work out %- take away final vol from total at start then divide by total and x by 100
- white phosphorus smoulders air to produce phosphorus oxide
what's the decomposition of hydrogen peroxide?
2H2O2 (aq) --> 2H2O (l) + O2(g)
-collect O2 over water using a delivery tube from flask to upside down cylinder
- use a gas syringe
how is the rate of hydrogen peroxide decomposition increased?
by adding a catalyst of manganese (lV) oxide
magnesium + oxygen ->
burns with bright white flame and white powder formed of 2MgO (s) which is slightly alkaline when dissolved in water
carbon + oxygen-->
burns with orange/yellow flame and produces CO2 (g) which is slightly acidic when dissolved in water
sulfur + oxygen -->
burns with pale blue flame and produces SO2 (g) which is acidic when dissolved in water
2 experiments to produce CO2
1) 2HCl + calcium carbonate CaCo3--> (CaCl2 (aq) + H2O (l) )+ CO2
- collected in gas syringe or using downward delivery
2) thermal decomposition of Metal carbonates- Copper carbonate
CuCO3 (s)--> CuO (s) + CO2 (g) heat CuCO3 a green powder decompose to co2 and copper(ll)oxide which is black
-collect gas using downward delivery
uses of CO2 (2 things)
1) in fizzy drinks because it is slightly soluble in water and dissolves under pressure CO2 + H2O --> H2CO3
2) fire extinguishers - Co2 is more dense than air so sinks onto flames and stops oxygen getting there
first 5 alkanes
1) Methane CH4
2) Ethane C2H6
3) propane C3H8
4) Butane C4H10
5) pentane C5H12
what's a homologous series?
the alkanes and alkenes can all be represented by the same general formula
- have same chemical properties
-same functional group
complete combustion :alkane + oxygen -->
carbon dioxide + water
incomplete combustion: alkane + oxygen -->
carbon + carbon monoxide + carbon dioxide + water
halogens react with alkanes to make ? in the presence of?
haloalkanes in UV light
methane + bromine -->
bromomethane + hydrogen bromide
molecules can make more bonds- double bong can open up
first 3 alkenes
1) Ethene C2H4
2) Propene C3H6
3) Butene C4H8
two structures of butene=
CH3-CH=CH-CH3 or CH2=CH-CH2-CH3
define an isomer
when two molecules have identical molecular formulas but different structures
how do you test for carbon-carbon double bonds?
bromine water (orange)+ alkene-->(shake) dibromoalkane (colourless) bromine molecules react with alkene so orange goes colourless
acid + metal oxide ->
acid + metal carbonate -->
salt + water + carbon dioxide
rate of reaction=
amount of reactant used or amount of product formed/time
3 types of reactions to measure rate of reaction
1) precipitation- marker disappears -subjective results
2) change in mass - gas given off- mass balance
3) the volume of gas given off - syringe
example of volume reaction for rate of reaction
HCl and Marble chips-> Co2 given off (changing surface area of marble chips, smaller means faster rate of reaction
example of change in mass for rate of reaction
magnesium metal + HCl -> hydrogen given off- effect of increased concentration on rate of reaction
example of precipitation reaction for rate of reaction
sodium thiosulfate + HCl -> cloudy precipitate of sulfur (yellow) effect of temperature or concentration
example of volume reaction producing O2 gas
decomposition of Hydrogen Peroxide 2H2O2 -> 2H2O + 02
effect of catalyst - manganese (ll) oxide- better catalysts give quicker rate of reaction- also measure effect of temp or conc of H2O2 solution
faster collisions only happen with
an increase in temperature
4 methods of increasing rate of reaction- collision theory
2) higher conc
3) large SA
measure the amount of energy transferred in a chemical reaction
how to carry out calorimetry test of dissolving, displacement or neutralisation reactions
1) mix reactants in a polystyrene cup
and record their temps before
2) take the temp every 30 seconds and record the highest temperature it reaches
3) to reduce heat loss to surrounding put polystyrene cup in a beaker with cotton wool surrounding it and a lid onto of cup to reduce energy lost by evaporation
how to carry out calorimetry test with combustion
1) reduce draughts using a screen
2) put 50g of water in the copper can and record it's temp
3) weigh the spirit burner and the lid
4) put spirit burner underneath can light the wick, stirring constantly until the temp is about 50
5)put out flame and measure final temp of water
6) weigh spirit burner and lid again