Quantitative chemistry Flashcards
How do you calculate the uncertainty of an experiment?
Find the range and divide it by two
(expressed by showing the mean then the +- symbol then the uncertainty e.g. 15.1 +- 0.2)
How do you calculate percentage yield?
% yield = mass of product you actually make / maximum theoretical mass of product x 100
Why do few reactions have a 100% yield?
Some of the reactants may not be completely pure
The reaction may be reversible
The reaction may produce more than one product that’s difficult to separate
What is the atom economy of a substance?
A measure of the amount of starting materials that end up in the useful product
How do you calculate the percentage of atom economy?
% atom economy = Mr of desired product / total Mr of all reactants x 100
How do you calculate moles when working with mass?
Moles = mass / Mr
How do you calculate moles when working with solutions?
Number of moles = concentration x volume / 1000
How do you calculate the volume of a gas with moles?
Volume (dm3) = 24 x moles
How do you convert dm3 to cm3
1dm3 = 1000cm3
What does the law of conservation of mass state?
That the mass of the reactants must equal the mass of the products
Why do some reactions appear to lose mass?
Because part of the product is a gas that escapes to the surroundings
Why do some reactions appear to gain mass?
Because the product reacts with gases in the air to form a compound
