C5.1 - Monitoring Reactions Flashcards
how do you calculate the percentage yield?
(real yield / theoretical yield)x 100
what does calculating the percentage yield show?
the efficiency of a reaction
define the term ‘actual yield’
mass of product made in a chemical reaction
define the term ‘theoretical yield’
maximum mass it is possible to make from a given mass of reactants (in perfect conditions)
define the term ‘percentage yield’
proportion of the theoretical yield actually obtained during a reaction
state 3 factors that prevent a percentage yield from reaching 100%
- reactants may burn in different ways than expected
- some reactants present may not react
- loss of some reactants
5.75g of sodium is reacted with chlorine to produce sodium chloride. If the actual yield is 10.2g, calculate the percentage yield. (4 marks)
2Na + Cl2 -> 2NaCl
10.2 / 14.625
= 70%
define atom economy
a measure of the amount of reactants that become useful products
what is the equation to calculate atom economy?
(sum of Mr of desired product / sum of Mr of all products) x 100
how much is one cm3 in dm3?
1 cm3 = 0.001 dm3
how much is 1 dm3 in cm3?
1 dm3 = 1000cm3
what is the equation to calculate concentration in g/dm3?
mass of solute (g) / volume of solution (dm3)
what is the equation to calculate concentration in mol/dm3?
amount of solute (mol) / volume of solution (dm3)
what are the factors when choosing g a reaction pathway?
5
- percentage yield of the product
- atom economy of the product
- usefulness of by-products
- rate of reaction
- equilibrium positions
if the atom economy of a process is high, how does it affect the efficiency?
it has a higher efficiency (less waste)
how does the by-product of a reaction affect the atom economy?
- if the by-product is useful the atom economy is higher (can sell it for another use)
- if not, the atom economy is lower
what makes the reaction pathway of a substance less desirable?
by products which are toxic, or of little use
what are titrations for?
to calculate the volume of acid/alkali needed to neutralise an acid/alkali
describe colour changes of methyl orange
yellow in alkali → red in acid
describe the colour changes of phenolphthalein
pink in alkali → colourless in acid
describe the process of how titrations are done (7)
1) add acid to a burette using a funnel, record the volume in the burette to start
2) add known volume of alkali to a conical flask
3) and add some indicator
4) place conical flask on a white tile (see colour change clearly)
5) add acid to alkali slowly until you see a colour change completely
6) calculate how much acid has been added (TITRE)
7) repeat until you get concordant titres
what is a burette?
a long graduated glass tube with a gap at the bottom
what is used to measure a alkali/acid when adding it to the conical flask?
volumetric pipette/ measuring cylinder
what must be used to fill a pipette safely?
pipette filler (the squeezy circle thing)
what is a titre?
the difference between the final burette reading and the inital burette reading?
describe two precautions needed to obtain a repeatable titre?
- burette must be clamped vertically
- flask must be swirled to mix contents
Define the term ‘limiting reactant’
- the reactant that is completely used up
- therefore, it limits the amount of product
how does the concentration of a solution relate to the mass of the solute and the volume of the solution?
smaller volume/ larger number of moles = higher concentration
larger volume/smaller number of moles = lower concentration
describe the relationship between molar amounts of gases and their volumes
- equal amounts of moles of gases occupy the same volume under the same conditions and pressure (RTP)
- volume (dm^3) = amount of moles x 24
how do you calculate the volume a gas takes up in room temperature (RTP - room temperature + pressure)
- if you have the number of moles
volume of gas at RTP (dm^3) = mol x 24
how do you calculate the volume of gas at RTP in cm^3
volume (cm^3) = mol x 24 000
