2. Amount of Substance Flashcards
Define a mole
The amount of substance that contains 6.022 x 10^23 particles
See questions in mixed batch containing:
Definitions of relative atomic mass, relative molecular mass and the Avogadro constant.
Compare the number of entities in 18g of water and 1g of hydrogen. (Mr of water = 18)
18g of water contains the same number of molecules as there are atoms in 1g of hydrogen
NB: Even if elements are usually found diatomically, you count the number of atoms e.g. In H2
What is the ideal gas equation?
PV=nRT
What does P represent in the ideal gas equation?
Pressure measured in Pa (Nm^-2)
What does V represent in the ideal gas equation?
Volume, measured in m^3
What does T represent in the ideal gas equation?
Temperature measured in K
What unit is R (in the ideal gas equation) measured in?
J K^-1 mol^-1
Do all gases obey the ideal gas equation?
No gases obey it exactly, but at room temperature and pressure it holds quite well for many gases.
Define ‘empirical formula’
The simplest whole number ratio in which the atoms in a compound combine together.
What does a solution consist of?
A solvent with a solute dissolved in it
What does the concentration of a solution tell us?
How much solute is present in a known volume of solution.
What is concentration measured in?
mol dm^-3
Give the two triangle formulas used in calculations in ‘Amount of Substance’.
/moles\ /mass\
/volume x conc\ /moles x Mr\
You must be able to:
Balance equations
Find ionic equations
Tips for balancing:
- It often takes more than one step to balance an equation, but too many steps suggest that you have an incorrect formula.
- When dealing with ionic equations the total of the charges on each side must be the same.
In a world of scarce resources it is not a good idea to waste unwanted products of a reaction. What is one technique that chemists use to assess a given process?
They determine the percentage atom economy.
Is atom economy theoretical or practical?
Theoretical
Give the equation for % Atom economy.
Mass of desired product
%Atom economy = _____________________ x 100
Total mass of reactants
Is percentage yield practical or theoretical?
Practical
Give the equation for % Yield.
Number of moles or grams of a product
% yield = ______________________________x 100
Theoretical number of moles/grams of a product
What problems can arise when trying to calculate ether percentage yield?
- Droplets get left in the apparatus
- Precipitate gets left in filter paper
- A reaction is reversible and a complete reaction does not take place (Haber process)
Ibuprofen production was improved because…
A new company were able to increase the percentage atom economy from 40% to 77%
