C3- Amount Of Substance And Moles Flashcards
What is meant by amount of substance?
Amount of substance, n, is a quantity used to count the number of particles in a substance.
Measured in mole, mol.
What is one mole?
The amount of substance that contains 6.02 x 10*23 particles.
One mole of atoms of any element = its relative atomic mass in grams.
What is avogadro constant?
6.02 x 1023 mole-1.
The number of particles in each mole of carbon-12
What is molar mass?
The mass per mol of a a substance.
Units= gmol*-1
What is the equation for amount of substance?
n = m / M
n= amount, mol m= mass, g M= molar mass
what is molecular formula?
The number of atoms of each element in a molecule.
What is empirical formula?
The simplest whole-number ratio of atoms of each element in a molecule.
What is relative molecular mass, Mr?
mass of a molecule compared with the mass of an atom of carbon-12
What is relative formula mass?
Compares the mass of a formula unit with the mass of an atom of carbon-12.
How do you find the empirical formula from mass?
- Convert mass into moles using n= m/M
- Divide both by the smallest number.
- Write the empirical formula
How do you determine the molecular formula?
- Convert % by mass into moles by using n=m/M
- Find smallest whole number ratio and empirical formula.
- Write relative mass of empirical formula.
- Find number of units in one molecule (Mr / relative mass of empirical formula).
- Write molecular formula ( empirical formula x ans to part 4).
Explain hydrated salts.
Many coloured crystals are hydrated meaning water molecules are part of their crystalline structure.
> this water is known as water of crystallisation. Shown in formula by a ⚫️
What happens when blue crystals of hydrated copper (II) sulfate are heated?
- the bonds holding water within crystal= broken and water is driven off.
- leaves behind white anhydrous copper (II) sulfate.
(Anhydrous= contains no water molecules)
What are the assumptions made in calculating an experimental formula?
- All water has been lost:
- you only aww the surface if crystals, some water may be left inside.
- if hydrated and anhydrous forms are similar colours, it’s hard to tell.
- No further decomposition:
- many salts decompose even further when heated. Can be difficult to judge if there is no colour change.
Equation for calculating amount,n in terms of conc and vol.
n = c x V
n= mol c= mol dm*-3 V= dm*3 (always convert if given in cm cubed)
What is a standard solution and how do you calculate its mass?
A solution of known concentration.
- Work out amount in moles required (n=cV)
- Work out molar mass (sum of Mr)
- Use n=m/M to calculate mass.
What is molar gas volume, Vm?
The gas volume per mole at a stated temp and pressure.
Units= dm3 mol-1
At RTP, molar gas volume= 24.0 dm3 mol-1
What is RTP?
Room temperature and pressure.
= 20*C and 101kPa (1 atm)
What is the equation for amount,n in terms of V and Vm?
n = V / Vm
n=mol
V= dm*3
Vm= 24.0
What are the assumptions made for molecules making up an ideal gas?
- random motion
- elastic collisions
- negligible size
- no IMF
What is the ideal gas equation?
pV = nRT
p=pressure, Pa V= volume, m*3 n= amount of gas molecules, mol R= ideal gas constant= 8.314 mol*-1 K*-1 T= temperature, K
(Conversions on notes)
What is stoichiometry?
The ratio of the amount (mol) of each substance in chemical equation
What are balanced equations used to find?
- quantities of reactants needed to prepare a required quantity of a product.
- quantities of products that should be formed from certain quantities of reactants.
What is theoretical and actual yield?
Theoretical- maximum possible amount of product.
Actual- obtained from reaction (lower than theoretical)
