- solids (s) -> giant ionic substances, metals, large simple molecular substances (I2), macromolecular structures (C, Si, SiO2) - liquids (l) -> relatively large simple molecular substances (H2O, Br2), Mercury (Hg) - gases (g) -> relatively small simple molecular substances (O2, HCl, CO2)

T5: Amount of Substance Flashcards by Aisha Imran

Hydrogen + Oxygen -> Water balanced equation

2H2(g) + O2(g) -> 2H2O(l)

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chemical formulae rules

elements written as 1 atom: all metals, noble gases, carbon, silicon (Na, Mg, Ca)
diatomic elements: N2, O2, F2, Cl2, Br2, I2
covalent compounds: formulae indicated by name (carbon dioxide -> CO2)
ionic compounds: determine from charges on individual ions

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state symbol rules

solids (s) -> giant ionic substances, metals, large simple molecular substances (I2), macromolecular structures (C, Si, SiO2)
liquids (l) -> relatively large simple molecular substances (H2O, Br2), Mercury (Hg)
gases (g) -> relatively small simple molecular substances (O2, HCl, CO2)

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Sodium + Water -> Sodium hydroxide + hydrogen balanced equation

2Na(s) + 2H2O(l) -> 2NaOH(s) + H2(g)

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Iron(III) oxide + Carbon -> Iron + Carbon dioxide balanced equation

2Fe2O3(s) + 3C(s) -> 4Fe(s) + 3CO2(g)

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Aluminium + Nitric acid -> aluminium nitrate + hydrogen balanced equation

Al(s) + 3HNO3(aq) -> Al(NO3)3(aq) + 1.5H2(g)

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compare the amounts of substance in both beakers

twice as many C atoms needed to make up 12g compared to Mg
each C atom has half the mass of a Mg atom
same mass doesn’t mean same number of particles

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Avogadro constant definition

the number of atoms in 12g of 12C

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molar mass unit

g mol-1

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number of particles in: 1 mole of Sodium Na+

6.022x10^23 ions of Na

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number of particles in: 2 moles of Silicon Si

2 x (6.022x10^23) atoms of Si

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number of particles in: 1 mole of hydrogen (H2) molecules

6.022x10^23 molecules of H2

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number of particles in: 3 moles of ammonia (NH3)

3 x (6.022x10^23) molecules of NH3

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how many atoms of H are in 2 moles of H2O

4 moles

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number of particles equation

Number of particles = Moles x Avogadro Number

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relative atomic mass (Ar) definition

(average mass of 1 atom of an element) / (1/12th the mass of 12C atom)

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relative molecular mass (Mr) definition

(average mass of 1 molecule) / (1/12th the mass of 12C atom)

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moles equation

n = M / Mr

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mass unit

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moles unit

mol

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concentration equation

c = n / V

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concentration unit

mol dm^-3

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volume unit

dm^3

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1cm^3 to 1dm^3

divide by 1000

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1dm^3 to 1cm^3

multiply by 1000

stage 1 of practical aspects of titrations (steps to make up a standard solution)

*Transfers know mass of solid* - weigh the sample bottle containing the solid on a (2dp) balance - transfer the beaker and reweigh sample bottle - record the difference in mass

stage 2 of practical aspects of titrations (steps to make up a standard solution)

*Dissolves in water* - add distilled / deionised water - stir (with a glass rod) or swirl - until all solid has dissolved

stage 3 of practical aspects of titrations (steps to make up a standard solution)

*Transfer, washing and agitation* - transfer to volumetric / graduated flask using a funnel - with washings - make up to 250cm^3 / mark with water - shakes / inverts / mixes

why remove any air bubbles from the burette tap

otherwise the volume of the air bubble will be counted in the burette reading (GREATER TITRE) (remove by opening tap first)

why remove the funnel used to fill the burette before starting the titration

solution drops could fall from the funnel into the burette and affect the burette reading (TITRE DECREASES)

why during the titration, swirl the conical flask and rinse the walls of the conical flask with distilled water

- ensures all reactants mix and no reagent is left unreacted on sides of flask - doesn't change the number of moles in conical flask so has no adverse effect on titration

% error (uncertainty) equation

(error of the equipment / amount measured) x 100

how does the error of the equipment change

error * (X -> depends on equipment used) - burette read twice so 2x error

how would you decrease % error in a titre measurement

increase the measurement made from the burette - increase the concentration of solution in conical flask - decrease the concentration of solution in burette

the ideal gas equation

PV = nRT

name P and it's units in the ideal gas equation

pressure Pa (pascals)

name V and it's units in the ideal gas equation

volume m^3

name n and it's units in the ideal gas equation

moles mol

name R and it's units in the ideal gas equation

gas constant = 8.31 J K^-1 mol^-1

name T and it's units in the ideal gas equation

temperature K (kelvin)

rearrange PV = nRT for P

P = nRT / V

rearrange PV = nRT for V

V = nRT / P

rearrange PV = nRT for n

n = PV / RT

rearrange PV = nRT for R

R = PV / nT

rearrange PV = nRT for T

T = PV / nR

dm^3 to m^3

divide by 1000

m^3 to dm^3

multiply by 1000

cm^3 to m^3

divide by 1 x 10^6

m^3 to cm^3

multiply by 1 x 10^6

°C to K

+ 273

K to °C

- 273

0°C is ?K

273

25°C is ?K

298

100°C is ?K

373

empirical formula definition

the empirical formula of a compound is the simplest whole number ratio of atoms of each element

molecular formula definition

the molecular formula of a compound is the actual number of atoms of each element

how do you remove all the water (water of crytalisation)

heat to constant mass

atom economy equation

% atom economy = (mass of desired products) / (total mass of reactants) x 100

why is it desirable to have a high atom economy yield

- increases the mass of atoms in the reactants that are turned into products - reduces the amount of waste by-products

how can atom economy be improved

atom economy can only be improved by finding a different reaction to produce the desired product which also produces fewer by products

what is the atom economy if only 1 product is produced

100%

percentage yield equation

(actual yield x 100) / theoretical yield

when using a chemical reactant to prepare to prepare a substance it is desirable to have a high % yield because:

- increases the amount of product that is made from the reactants - % yield can be increased by making improvements in experimental technique