Topic 2 - reaction quantities Flashcards
Molarity
Standard solutions are made and used for chemical analysis
They are solutions of a specific, known and tested concentration, usually measured in terms of molarity
When one mole of solute is dissolved in 1 cubic decimetre (1 litre or 1000ml) of solution, it’s concentration is written as:
1 mol dm-3
This can be written as 1M for short.
This is the molarity of the solution
Calculating molarity
how many moles of hydrochloric acid are there in 100cm3 of 1m hydrochloric acid solution.
number of moles (N) = molarity (C) x volume of solution V) (dm3)
volume is given in 100cm3 so needs to be converted to dm3 by dividing by 1000 (1 dm3 = 1000cm3)
no moles = 100/1000 x 1
= 0.1 moles
Reacting Quantities
The relationship between the reactants and products in a chemical equation can be used to work out how much product will be produced from given amounts of reactants
This is called stoichiometry
We can also work out how much of a reactant is needed to produce a given amount of product
Calculating reaction quantities
50g of CaCO3 are heated how much CaO will be formed
1) First write a balanced equation: CaCO3(s) → CaO(s) + CO2(g)
2) Then calculate the Mr of the substances we are interested in:
CaCO3 40 + 12 + (3 x 16) = 100
CaO 40 + 16 =56
3) Calculate the number of moles of CaCO3 used.
n=mass/Mr 50/100 = 0.5 mol
4) From the equation we can see that one mole of CaCO3 produces one mole of CaO.
Therefore 0.5 mol of CaCO3 produces 0.5 mol of CaO.
5) Finally calculate the mass of 0.5 mol of CaO:
n=mass/Mr, mass=Mr x n, 0.5 x 56 = 28g
Therefore 50g of CaCO3 produces 28g CaO
Percentage Yield
how mass can be lost
The theoretical mass is the maximum amount of product you can get from a given amount of reactant
In most reactions you won’t actually get this….
Some can be lost when transferring between containers
Some can be lost during separation techniques
Some may react with impurities
Some of the reactants might make something else
The reaction could be reversible
To find out how efficient your reaction is, you calculate percentage yield
Calculating percentage yield
Percentage yield = actual mass / theoretical mass x100
OR
Percentage yield = actual no of moles / expected no of moles x100
explain how burning carbon in air can ;head tp the formation of carbon monoxide
air contains oxygen
if oxygen limited incomplete combustion occurs (carbon monoxide forms)
