amount of substance and the mole + determination of formulae + moles and volume

amount of substance (n)

quantity used to count the number of particles in a substance, measures in a unit called the mole (mol)

Avogadro’s constant

6.02× 10²³

the number of particles per mole

number of particles equation

number of particles = number of moles x 6.02× 10²³

moles equation

moles = mass ÷ mr

the molecular formula

the number and type of atoms of each element in a molecule

the empirical formula (2)

the simplest whole number ratio of atoms of each element present in a compound.

important for substances that do not exist as molecules → form giant crystalline structures of atoms or ions ~→ too many atoms to base a formula on.

finding empirical formulas experimentally

need to write up and revise

hydrated

anhydrous

water of crystallisation

hydrated - contains water

anhydrous - does not contain water

water of crystallisation - water molecules part of the crystalline structure

percentage error =

. (amount of mass measurements taken) x uncertainty (in each measurement)

percentage error = ———————————————————————————————————— x 100

. quantity measured

how does quantity measured affect the percentage error?

incr. quantity measured or more readings taken = smaller % error

dm cubed → m cubed

DIVIDE 1000

concentration equation

mass = conc. x vol ( of what its dissolved in)

density equation

mass = dens x vol

at room temp and pressure

1 mol of a gas will have…

what volume?

how many molecules?

24dm³

6.02×10²³

molar volume (2)

the volume occupied by 1 mole of any gas at room temp and pressure

24

RTP

temp - 20*C

pressure- 101KPa (1atm)

equation linking moles and gas volumes

to convert from vol of gas to mol no. for room temp and pressure

mol x 24 = volume (dm³)

ideal gas equation

to convert from vol of gas to mol no. for any temp and pressure

pV = nRT

p= pressure (Pa)

V= volume (m³)

n= amount of gas molecules (mol)

R= ideal gas constant= 8.314 J mol⁻¹K⁻¹

T= temp (K)

dm³→m³

cm³→m³

divide 1000

divide 1,000,000

*C → Kelvins

+273

ideal gas constant

8.314 J mol⁻¹K⁻¹

assumptions made about ideal gases (4)

• random motion

• elastic collision

• negligible size

• no intermolecular forces

stoichiometry

the ratio of the amount, in moles, of each substance

theoretical yield

actual yield

the mass of a product we should get in a reaction = theoretical yield

the amount of product obtained when you actually do the experiment = actual yield

percentage yield

. actual yield

%yield = ——————- x100

, theoretical yield

% yield is never 100% (3)

• reaction may be incomplete - hasnt been left log enough

• product may be lost in transfer - container transfers

• unwanted side reactions - make unwanted products

atom economy

def + equ

the percentage of reactants that are converted to useful product

limiting reactants

excess reactants

limiting reactants - reactant used up when the other is left over (controls amount of product formed)

excess reactants - left over reactant