C1 - Quantitative Chemistry Flashcards
What is relative formula mass?
The relative atomic masses of all the atoms in the molecular formula added together
What is the symbol of relative formula mass?
M (little) r
What is the symbol for relative atomic mass?
A (little) r
How do you find relative atomic mass?
It is the same as mass number
How do you find the relative formula mass?
Add up the relative atomic masses of all the atoms in the compound
How do you calculate the percentage mass of an element in a compound?
(A,r x number of atoms of that element) / (M,r of the compound) x 100
What is a mole?
In book
In a chemical reaction, mass is always?
Conserved
What happens to atoms in a chemical reaction?
Nothing, they can not be destroyed or created
What can cause mass to seem to change?
Gases
1 way gas makes mass seem to increase?
One of the reactants is a gas found in air, and the products are solid, liquid or aqueous. Before the reaction, you cannot account for the gas in the airs mass as it is floating around. When it reacts the gas becomes part of the product, causing a seemingly increased mass.
1 way gas makes mass seem to decrease?
One of the products is a gas and the reactants are solid, liquid or aqueous. Before the reaction, all the reactants are contained, but after, it is no longer contained and may cause the mass to appear to have decreased.
What are limiting reactants?
If one reactant gets completely used up in a reaction before the rest, stopping the reaction.
What is the amount of limiting reactant directly proportional to?
The amount of product formed.
At the same temperature and pressure, equal numbers of moles of any gas will occupy the same….
Volume
At room temperature and pressure (20C and 1atm) one mole of any gas occupies….
24dm^3
Formula to find the volume of a known mass of any gas at room temp and pressure (rtp)
Volume of gas = mass of gas/Mr of gas x 24
Volume dm^3
Mass in grams
How do you calculate the concentration of a solution in g/dm3?
mass of solute/mass of solvent
How do you calculate the concentration of a solution in moles?
number of moles of solute/volume of solute
Titrations
In book
What is meant by atom economy/utilisation?
What percentage of reactants form useful products
100% means all are useful
What is the formula for atom economy/utilisation?
relative formula mass of desired products/relative formula mass of all reactants x 100
What are the benefits of high atom economy?
Lack of waste means it is greener, better for the environment, cheaper and more sustainable
What is percentage yield?
The amount of product you get from a reaction
How do you calculate percentage yield?
mass of product actually made/maximum theoretical mass of product x 100
Can a yield be 100%?
No
How do you lose yield?
- Not all reactants react to make a product, due to being reversible
- There may be side reactions
- You may lose product when spectating it from the reaction mixture
Why is a high yield good?
Lack of waste and higher profit
