FULL TOPIC 3: QUANTITATIVE CHEMISTRY

Avagadro's Constant

6.02 x 10^23

Law of conservation of mass

no atoms are lost or made in a chemical reaction

Mole

a unit to measure chemical amounts

Actual yield

the mass that is made in the chemical reaction

Theoretical yield

the maximum mass that is possible to make from a given mass of reactants

Instrumental method

machine based method used to analyse substances

Percentage atom economy

measures how much of the reactants end up in useful product

Random error

measured values vary randomly, very common, due to human error + random variations

Systematic error

issue in experimental design or equipment causes the measured value to be consistently too high or too low

Percentage mass of an element in a compound

Ar x number of atoms of that element / RFM of the compound x 100

Calculate moles

mass (g) / RFM

Atom economy

RFM of desired products / relative formula mass of all reactants x 100

Percentage yield

mass of product actually made / maximum theoretical mass of product x 100

How do you find the ratio?

You look at the big numbers

Calculating concentration

concentration (g/dm3 or mol/dm3) = moles/volume (dm3)

Calculating gas volumes

no. moles x vol. 1 mole (24)

Calculating uncertainty

range / 2

Uncertainty in an instrument

1/2 of the smallest division (e.g., a ruler extends to 0.5 cm (5mm) so the uncertainty in the instrument is 0.5 / 2 = 0.005)

Calculating limiting reagents

1. Write the balanced equation

2. Determine the molar ratio

3. find the moles of each product (mass/RFM)

4. Fit the moles into the ratio