topic 5 Flashcards
what is a mole definition
measuring amount of substance
what number is a mole
avogadros number
6.02 x 10^23 atoms/molecules
how to work out number of particles
avogadros x moles
how to work out moles
mass / Me
cslculate the number of moles in 23g of gold
23/197
= 0.12 mol
how to work out moles in solution
conc. (moldm-3) x vol (dm3)
how to work out conc. in gdm-3
mass/vol
calculate moles of 200cm3 of 0.35 moldm-3 HCl
0.35 x 200x10-3
= 0.07 mol
what is empirical formula
simplest whole number ratio of elements in a compound
how to work out empirical formula
- write out elements involves
- write % as masses
- divide these by Mr to get moles
- divide all by smallest number of moles
work out empirical formula od a compound that contains 23.3% Mg, 30.7% S, 46% O
- Mg S O
- 23.3g 30.7g 46g
- 24.3 32.1 16
= 0.96 0.96 2.88 - 1 1 3
MgSO3
work out the empirical formula when a hydrocarbin combusts completely to make 0.845g of CO2 and 0.173g H2O
1write H2O and CO2 headings
2. write doem masses
3. divide by Mr to get moles
4. divide number of C and H atoms by smallest moles
CO2 H2O
0.845g 0.173g
——— ———
44 18
=0.019 =0.0096x2=
0.0192
/ 0.019=1 /0.019=1
CH
how to work out molecular formula from empirical
work out Me of empirical/ Mr molecular
x atoms in empirical
what do ionic equations show
ions formed in solution and which particles are reacting
how to work out ionic equations
axe aq
ditich doubles
what is the ionic equation of H2SO4 + 2KOH –> K2SO4 + 2H2O
2H^+ + SO4^2- + 2K^+ + 2OH^- –> 2K^+ + SO4^2- + 2H2O
2H^+ + 2OH^- —> 2H2O
how to work out theoretical masses
- write equation and balance
- work out Mr and write as masses
- find 1 gram of compound you know the mass of x mass, divide other compound by this and x same
how much CaO can be made when 34g Ca burnt in O2
- 2Ca(s) + O2 (g) —> 2CaO (s)
- 40x2 = 80g 56x2 =112g
- /80=1g /80=1.4
x34 = 34g x34 = 47.6g
= 47.6g
what is a displacement reaction
more reactive element takes place of less reactive element in compound
what is an acid base reaction
form salt and water
carbonates produce carbon dioxide as well
what is a precipitation reaction
solid produced after 2aq reactants react
how to work out moles from volume and molar gas volume
volume/molar gas volume
what is molar gas volume at room temperature and pressure
24 dm3 mol-1
what is molar gas volume at standard temperature and pressure
22.4 dm3 mol-1
how much gas in cm3 is produced when 6.2g of Mg reacts with HCl at rtp
Mg(s) + 2HCl(aq) —> MgCl2 (aq) + H2 (g)
Mr Mg = 24.3
mol Mg = mass/Mr = 6.2/24.3 = 0.255 mol
Mg:H2 1:1 ratio so H2 mol = 0.255
volume = mol x molar gas volume = 0.255 x 24 = 6.12 dm3
= 6120 cm3
calcualte amount of gas produced when 5.6 dm3 of N2O decomposes
N2O (g) —> N2(g) + 0.5 O2(g)
1 mol N2O produces 1 mol N2 and 0.5 mol O2
1.5 mol produced overall
1.5x5.6 = 8.4 dm3
what is the ideal gas equation and all units
pV=nRT
p- pressure (Pa)
v- volume (m3)
n- moles
R - gas constant 8.31 JK-1mol-1
T - temperature (K)
how to convert m3 to dm3 to cm3
m3–>dm3 ‘
x1000
dm3–>cm3 x1000
what volume of H2 produced when 12g of K reacts with H2O at 100KPa and 298K, gas constant 8.31
2K(s) + 2H2O (l) –> 2KOH (aq) + H2(g)
mass/ Mr 12/39= 0.31mol of K
2 moles K produces 1 mol H2 0.31/2=0.155 mol H2
v=nRT/p
v = 0.155x8.31x298/100,000
= 3.84x10^-3 m3
what is a hazard
things that could cause harm
what is a risk
likelihood of harzard causing harm
eg
scalding from hot liquids
burns from hot equipment
burns from chemicals
cuts from glass/metals
what is a risk assessment
identification of all hazards and risks associated
likelihood of something going wrong
seriousness of risk
how to reduce risk
how to make a standard solution
weigh - weigh amount of solid precisely using balance and weighing boat
transfer- transfer solid from weighing boat to beaker, wash any solid left into beaker using distilled water
disolve- dissolve solid fully using distilled water, stir to ensure fully disolved
transfer- transfer solution to volumetric flask using funnel, rinse beaker and glass rod into flask
fill- use more distilled water to fill to graduation line, use pipette when near
mix - invert flask to ensure solution fully mixed
what mass of solid NaOH is required to make 250c,3 of 0.75 mol dm-3 NaOH solution
work out moles
conc. x vol
0.75 x 250x103 = 0.1875 mol
use moles to calculate mass
mol x Mr
0.1875 x 40 = 7.5g
how does a titration take place
have known acid or alkali in burette with known conc.
have known volume of unknown acid or alkali conc. in conical flask
add chemical in burette to conical flask until indicator changes
read how much chemical was added to neutralise chemical in flask, read from bottom of meniscus
18.3 cm3 0.25 moldm-3 HCl required to neutralise 25cm3 KOH, calculate conc. KOH
- write equation and balance
HCl + KOh –> KCl + H20 - calculate moles of HCl conc x vol
0.35 x 18.3x10-3 = 4.58 x10-3 mol - use equation to find molar ratio
1:1 HCl : KOH
moles KOH = 4.58 x10-3 - conc.= moles/vol
4.58x10-3 / 25x10-3 = 0.18 mol
what is an uncertainty
degree of error your measurements have
hald the smallest increment on equipment
if you are using more then one measurement with the same units you add uncertainties
how to calculate % uncertainty
uncertainty / reading
x100
what are systematic errors
caused every time
what are random errors
caused through estimating readings
vary
how to calculate % yeild
actual/theortical
x 100
what is theoretical yield
amount of product produced assuming no products lost and all reactants fully react
how to calculate atom economy
Mr of desired product / sum of Mr of all reactants
x100
what is atom economy
how efficient a reaction is
what is the importance of atom economy
- high atom economies produce less waste so benefit environment
- high atom economies means that raw materials are used more efficiently, more sustainable
- companies will try to use reactions that tend towards 100% atom economies
- high atom economy means less by products so less time and money separating these from desirable product
