C2.6 Quantitative chemistry Flashcards
What is the relative formula mass, M_r of substance?
The sum of the relative atomic masses of all the atoms or ions in that substance
How do you work out the empirical formula?
- you find the mass of each element in grams and their relative atomic masses
- you divide the mass of each element by its relative atomic mass
- divide the answers by the smallest number to find the simplest ratio
- the result is the number of each atom in the empirical formula
How do you calculate the percentage mass of each element in a compound?
number of atoms of element x relative atomic mass/relative formula mass x 100
What is the yield?
The amount of useful product obtained from a reaction
What is theoretical yield?
The theoretical calculated yield of reactions
How do you find the percentage yield?
Actual yield/theoretical yield x 100
What is actual yield?
The amount of product obtained from the reaction in real life
What is the percentage yield?
A comparison of the actual yield in relation to the theoretical yield
What are three reasons the actual yield is less than the theoretical yield?
- the reaction may be incomplete
- some of the product is lost during the practical preparation
- there may be other unwanted reactions taking place
What are by-products?
Substances produced from a reaction that aren’t needed
What are waste products?
By-products that aren’t useful
What are some problems associated with the disposal of waste products?
- it’s expensive (may have to be transported to a landfill site or treated with another substance to make it safe)
- can cause environmental problems
- can cause social problems, e.g. house prices may drop if a chemical plant is built near them
How do chemical companies increase profit?
- by making the percentage yield is high
- making sure the by-products of all the reactions are useful
- by making the reaction take place quickly
How can waste products be made economically viable?
By finding a use for them
