What is 1mol of atoms equal to? (Avagadro)
6.02x 10[23] carbon atoms
How do you find Mr?
add the Ar’s of each element in compound
(e.g CO2 = 1x12 + 2x16 =44 )
The amount of moles of a given mass substance is calculated using:
moles = mass/ Mr
What is the limiting reactant?
The reacting substance that is completely used up in a chemical reaction
The concentration of a solution can be calculated using:
concentration (mol/dm[3]) = amount of solute (mol) / volume (dm[3])
how can you convert from cm[3] to dm[3]?
divide by 1000
how can you convert from dm[3] to cm[3]?
x 1000
how can you convert mol/dm3 to g/dm3?
x Mr
how can you convert g/dm3 to mol/dm3?
divide by Mr
How do you calculate atom economy?
Total Mr of desired products/ Total Mr of all reactants x100
What is atom economy?
A measure of how many reactant atoms form a desired product.
what is theoretical yield?
The maximum possible mass of a product that can be made in a chemical reaction
why might actual mass not be the maximum theoretical mass?
- the reaction not going to completion, because it is reversible
- some of the product may be lost when it is separated from the reaction mixture
- some of the reactants may react in ways different to the expected reaction
- spillages
how can you calculate percentage yield?
mass of product made/ maximum theoretical mass x100
How can you calculate volume of a gas?
Number of moles x molar gas volume
What is the molar gas volume?
the volume of any gas at standard conditions of 20C and 1 atmosphere pressure, it is a fixed volume of 24dm[3]
what apparatus is needed for titrations?
- burette
- pipette and filler
- conical flask and white tile
What reagents are needed for titration?
- an acid (hydrochloric, sulfuric or nitric) of unknown concentration
- sodium hydroxide solution of known concentration
- a suitable indicator, for example methyl orange or phenolphthalein
- ## NOTE: known goes in flask, unknown in buerette
What is the method for titration?
- Use the pipette and pipette filler to add 25 cm3 of alkali to a clean conical flask.
- Add a few drops of indicator and put the conical flask on a white tile.
- Fill the burette with acid (known) and note the starting volume.
- Slowly add the acid from the burette to the alkali in the conical flask, swirling to mix.
- Stop adding the acid when the
end-point is reached (when the indicator first permanently changes colour). Note the final volume reading. - Repeat steps 1 to 5 until you get
concordant titres
what are concordant titres?
Titres within 0.10 cm³ of each other.
Explain why a pipette is used to measure the alkali, rather than a measuring cylinder.
The pipette allows the same volume of alkali to be added each time, helping to make the results repeatable.
Mols=
Mass/Mr
Mass is always
Conserved
Volume of any gas =
Mol x 24
