key equations moles and amount of substance Flashcards
= (mass-m-)/( molar mass -M-) and give all 3 units within this equation
(Molar mass is numerically equal to relative molecular/formula mass.)
moles=
moles- mol
mass- g
molar mass- gmol^-1 (mass number)
= moles x Avogadro’s constant
no.particles=
where particles refers to atoms, molecules, or ions, electrons.
=conc x vol
and give all 3 units within this equation
moles
moles- mol
vol- dm^3
conc- moldm^-3
=nRT
and give all 5 units within this equation
pV
pressure- pa
vol-m^3
moles(n)- mol
temperature - k(celcius + 273)
R- constant(8.314 Jk^-1mol-1)
=mass/volume
density
mass- g
vol- cm^3
density- gcm^-3
%atom economy =
100x (Mr of desired product/Mr of all reactants)
% yield=
100x (actual yield/theoretical yield)
equation
relative atomic mass or relative intesity=
((Isotope1 mass x abundance1 or intensity2) +(isotope2 mass x abundance2 or intensity2)… ) / total abundance or total intensity
cm^3 to dm^3
divide cm^3 by 1000
cm^3 to dm^3:
To convert g dm-3 to mol dm-3:
relative atomic mass=
% yield=
%atom economy =
=mass/volume
=nRT
=conc x vol
= moles x Avogadro’s constant
= (mass-m-)/( molar mass -M-)
Molar mass - is numerically equal to relative molecular/formula mass.
cm^3 to dm^3: divide cm^3 by 1000
To convert g dm-3 to mol dm-3:Divide the concentration in g dm-3 by the Mr of the solute
relative atomic mass= ((Isotope1 mass x abundance1) +(isotope2 mass x abundance2)… ) / total abundance
% yield= 100x (actual yield/theoretical yield)
%atom economy = 100x (Mr of desired product/Mr of all reactants)
density =mass/volume
pV =nRT
moles =conc x vol
no.particles = moles x Avogadro’s constant
moles = (mass-m-)/( molar mass -M-)
To convert g dm-3 to mol dm-3:
Divide the concentration in g dm-3 by the Mr of the solute
To convert mol dm-3 to g dm-3:
Multiply the concentration in mol dm-3 by the Mr of the solute
how can we
use the percentage mass contribution of each element to calculate the empirical formula of a compound (4)
1.Assume a total sample size of 100 g - this simplifies the calculation as percentage values directly translate to grams.
2.Calculate the moles of each element based on its percentage mass.
3.Divide the mole values by the smallest mole number among them to simplify the ratio to its lowest form.
4.Construct the empirical formula from this simplified mole ratio.
how can we
use the masses of products from combustion reactions to calculate the empirical formula of a compound (4)
1.Determine moles of products using their mass and molar mass.
2.Infer moles of each element in the original compound from the product moles.
3.Simplify to the lowest whole number mole ratio.
4.Derive the empirical formula from this ratio.
how can the formula of a hydrated ionic compound can be determined experimentally(4)
1.Heat the hydrated salt to remove water, leaving anhydrous salt.
2.Calculate moles of water lost and anhydrous salt remaining.
3.Find the mole ratio of salt to water.
4.Express this ratio in the formula as a whole number.
how can the formula of a hydrated ionic compound can be determined via calculation
1.Heat the hydrated salt to remove water, leaving anhydrous salt.
2.Calculate moles of water lost and anhydrous salt remaining.
3.Find the mole ratio of salt to water.
4.Express this ratio in the formula as a whole number.
Determining the molecular formula from empirical formula
A compound has an empirical formula of CH and a molar mass of 78.0 g mol-1.
Determine its molecular formula.
Step 1: Calculate empirical formula mass
C: 12.0 g mol-1
H: 1.0 g mol-1
Empirical formula mass = 12.0 + 1.0 = 13.0 g mol-1
Step 2: Divide molecular mass by empirical formula mass 78.0/13.0=6.0
Step 3: 6 x CH
Step 4: Write the molecular formula
The molecular formula is C6H6.
A hydrocarbon sample weighing 2.20 g was completely combusted in oxygen, producing 3.30 g of CO2 and 1.35 g of H2O.
Determine the empirical formula of the hydrocarbon.
Step 1: Calculate moles of CO2 produced
n CO2= mass/mr = 3.30/44.0=0.075
Step 2: Calculate moles of carbon in the sample
Each molecule of CO2 contains 1 atom of carbon.
Moles of C atoms = 1 x Moles of CO2 = 0.075 mol
Step 3: Calculate moles of H2O produced
n H2O= mass/mr = 1.35/18.0=0.075
Step 4: Calculate moles of hydrogen in the sample
Each molecule of H2O contains 2 atoms of hydrogen.( just cuz there are 2 hydrogens in H2O )
Moles of H atoms = 2 x moles of H2O = 2 x 0.075 = 0.150 mol
Step 5: Determine the simplest C : H mole ratio
C : H = 0.075 : 0.150 = 1 : 2
Step 6: Write the empirical formula
The empirical formula is CH2.
Ionic Compounds are aka Salts true or false
true
What products are formed when I(capital i) reduces H₂SO₄Do equations for all 4.
1)H2SO4 + 2I→ SO4^2- + 2HI
2)H2SO 4 +(2H^ +) +(2l^ -) → SO2 + I2 + 2H2O (SO₂ is a choking gas with a pungent odour)
3)H2SO4 + (6H^+) +(6l^ -)→ S + 3l2 + 4H2O (S is a yellow solid)
4) H2SO4 + (8H^+) +(8l^ -) → H2S + 4l2 + 4H2O (H₂S smells of bad/rotten eggs)
mass of 1 mole of an element/mass of 1 atom of an element =
Avogadro’s constant
(mass number of element x 10^-3)/ Avogadro’s constant =
= mass in kg
Bromine has two isotopes, 79Br and 81 Br. At what values of m/z would you expect to find lines in the mass spectrum of bromine, Br? (Assume that only 1+ ions are formed.) -
There would be lines at 79 and 81
There would also be lines at 158 (79 + 79), 160 (79 + 81) and 162 (81 + 81)
