C2 - Quantitative Chemistry Flashcards
What is an empirical formula?
A formula that gives the simplest whole number ratio of atoms in a compound
Describe how you calculate an empirical formula
Mass / relative atomic mass for each component
Divide each calculated number by the smallest of the 2 numbers calculated
Round to the nearest whole number
Put numbers into a ratio representing the components of the compound
The ratio should represent the number of atoms for the elements such as 1:2 being MnO^2
Show how you would calculate the empirical formula of magnesium oxide? (The magnesium is 2g and the magnesium oxide is 3.25g)
3.25 - 2 = 1.25 2 / 24 (magnesium relative AM) = 0.0833 1.25 / 16 (oxygen RAM) = 0.0781 0.0781 is smallest 0.0781 / 0.0781 = 1 0.0833 / 0.0781 = 1.0665 1.0665 is rounded to 1 (nearest whole number So the ratio of the magnesium to the oxygen in the magnesium oxide is 1:1 This means the formula is MgO
Why is empirical formula used?
It is a quick and accurate estimate of the molecular formula
However, it isn’t always right
What is green chemistry?
The idea of making chemicals so that they endure the test of time and meet the needs of humans today and in the future
What are the 7 factors that affect the sustainability of chemical production?
Feedstocks (renewable feedstocks needed)
Atom economy (high percentage)
Waste (minimised)
Energy in and out
Social and economic benefits (as much as possible)
Environmental impact (must be low)
Health and safety (processes can’t put workers in danger)
How do you calculate atom economy?
Molar mass of atoms in desired products / molar mass of atoms in reactants * 100 (percentage)
How do we make sure chemical processes are safe?
Hazard symbols
Regular checks
How could newly discovered chemicals be potentially hazardous?
We don’t know their long-term health effects yet so there are no hazard signs
What is percentage yield?
The amount of product received compared with the amount of product expected
What is the formula for calculating percentage yield?
Actual yield / maximum theoretical yield * 100 (percentage)
How do you calculate the maximum theoretical yield?
Add together the molar masses of all the atoms in the reactants
The molar mass of an atom of the element should be the relative atomic mass in grams
What are the 3 reasons that a percentage yield is under 100%?
The reaction is reversible (reactants never completely converted to products)
Filtration (you always lose some of the substances)
Unexpected reactions (there can often be other reactions happening that use up the reactants)
