Booklet 3 - Chemical Measurements... Flashcards
What is Relative atomic mass?
The average mass of all isotopes
What is relative formula mass?
It is similar to relative atomic mass, however it deals with formulae.
What can the formulae be in relative formula mass?
Can be elements or compounds
How do we find relative formula masses?
By adding the relative atomic masses together
What is the conservation of mass?
- It is when the same atoms are present at the start and end of the reaction, this means mass must have been conserved.
- i.e the total mass of the reactants must equal the total mass of the products.
How does using the Ar/Mr values and the conservation of mass help us?
It helps us to predict the masses of reactants and products in reactions.
What is Avagadro’s number?
6.02x1023 which is equal to 1 mole
What is the symbol unit for moles?
Mol
What can measurements of amounts in moles apply to?
Atoms, molecules, ions, electrons, formulae, equations.
What is the mathmatical equation for linking moles and mass?
Mass (g) = Mr x moles (n)
What can the masses of reactants and products be calculated from?
Balanced symbol equations
If you already have the masses of reactants and products what can you do? What is it called?
Use them to find out the ratio of reactants to products. It is called Stroichiometry
When a small amount of hydrogen gas is ignites with oxygen in a test tube during the squeaky pop test. What is all of the hydrogen is converted into?
Water vapour
What is the oxygen from air involved in the reaction present in? What happens to the hydrogen?
Present in excess, there is more oxygen present than is necessary. The hyrdogen reacts and runs out before the oxygen does.
What is the hydrogen said to be?
The limiting reactant, it limits the amount of water vapour produced.
When reacting sodium metal in a large water trough, the sodium will completely react bedore the water is even close to being used up. What is the sodium?
The limiting reactant as once it has reacted no futher hydrogen gas is porduced and the fizzing stops.
What is common in a chemical reaction involving two reactants?
It is common to use one of the teactabts in excess to ensure that the other reactant, i.e the limiting reactant is used completely
What is the concentration of a solution?
The amount of solid material (solute) dissolved in a certain colume of liquid (solvent).
What does the concentration become when there is more solute in the liquid?
More concentrated the solution becomes
What is concentration measures in?
Grams of substance per cubic decimetre of water (g/dm3)
What is the general formula for concentration?
Concentration g/dm3 = mass (g) ➗volume in (dm3)
What are the 3 reasons that is may not be possible to obtain the calculated amount of product?
1) . The reaction may not go to completion
2) . Some product may be lost when it is separated from the reaction mixture
3) . Some of the reactants may react in ways different to the expected reaction (side reactions)
What is percentage yeild?
The amount of product obtained is known as the yield when compared with the maximim theoretical amount as a percentage.
What is the equation for percentage yield?
%yield = mass of product actually made ➗ theoretical mass of product
What is atom economy?
Also called atom utilisation it is a measure of the amount of starting materials that end up as useful products.
Why is it important to use reactions with a high atom economy?
It is important for sustainable development and for economic reasons as this will lead to less wasteage of atoms.
What is the equation for percentage atom economy?
% atom economy = mass of useful product ➗ total mass of reactants. X 100
What is the equation for converting g/dm3 to mol/dm3 ?
Moles = mass➗Mr
What is the equation for converting from mol/dm3 to g/dm3?
Mass = moles x Mr
What is the equation for concentration using the unit of Mol/dm3?
Concentration in mol/dm3 = moles ➗ volume (dm3) (rearranged from moles = concentration (mol/dm3) x volume)
What is the volume of 1 mole of any gas at room temperature and preassure?
24dm3
What is the equation to work out the volume of any gas?
Volume of any gas = moles (n) x 24
What is the equation for concentration in g/dm3 ?
Concentration g/dm3 = mass (g) ➗volume in dm3
What is the limiting reactant?
The reactant that us completely used up, it limits the amount if products
