C4 - Chemical Calculations
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formula moles mol
moles = mass / molar mass mol = g / Mr
What are the three types of yields? How are each type of yield found?
• percentage yield - how much product was made compared with the amount of product expected • theoretical yield - maximum mass of product possible • actual yield - given in the question
How do you find the percentage yield?
percentage yield = actual yield / theoretical yield
How is the theoretical yield found?
The Mr
Why will the percentage yield never be 100%?
• Chemical reactions will never fully react • Residues - some chemicals lost through physical transfers • Sideways reactions
define atom economy
The amount of reactants that end up as useful products. It is a way of measuring efficiency.
formula atom economy
atom economy (%) = Mr of useful product / sum of Mr of all products
Why does industrial manufacturing require a high atom economy for chemical reactions?
• reduces production of unwanted products • makes the process more sustainable
What are the factors that should be taken into consideration for carrying out chemical reactions?
• % yield • atom economy (%) • energy requirements • toxicity of waste • rate of reaction - the speed of the reaction • availability of reactants
How many atoms are in 1 mole? What is the name of this constant?
6.02 x 10 23 Avogadro’s constant
formula: concentration
concentration = mass or moles / volume concentration = (g | mol) / dm3
1dm3 to cm3
1dm3 = 1000cm3
define titration
Technique that can be used to analyse the concentration of substances in a solution accurately.
define in excess
More than enough of a substance to react with another reactant
define limiting factor
Not enough of a substance to react with another reactant
how do you work out the unknown concentration of a solution using the known concentration of a solution?
(volume of known * concentration of known) / volume of unknown only applies if the mole ratio is 1:1, otherwise use a table
List the steps to find the concentration of an alkali NaOH, using an acid HCl with a known concentration.
• fill the burette up to the 0cm3 mark with the HCl • use a pipette filler to fill a pipette with NaOH, and write down the volume • pour the precisely measured volume of NaOH into a round bottom beaker • use 1 or 2 drops of phenolphthalein to change the colour to pink, not purple • open the burette and let the HCl drain into the round bottom beaker. Swirl the solution while doing this. • close the burette when the solution turns colourless. record the volume of HCl used to neutralise the NaOH. • repeat 3 more times
What indicator is used in acid-base titrations?
phenolphthalein FEE + NOL + THAY + LEE + IN
What colour is phenolphthalein in: a. acidic solutions b. basic solutions
a. colourless b. pink ‘pink is basic’
volume of 1 mole of any gas at standard room temperature and pressure
24dm3
masses to balanced equations steps
• find Mr • find mol • divide mols by the smallest amount to get integers
what is avagadros constant
how many atoms there is in a mole 6.02 * 1023