C3: Quantitative chemistry Flashcards
State the law of conservation of mass
No atoms are gained or lost in a reaction
Mass appears to increase during a reaction if …
One of the products is a gas
Mass appears to decrease during a reaction if…
One of the products is a gas and it has escaped
Balanced symbol equations;
Represent chemical reactions and have the same number of atoms of each element on both sides of the equation
Chemical amounts are measured in …(4)
Moles.
- mass of one mole of a substance in grams = relative formula mass(Mr)
- one mole of a substance will contain the same number of particles, atoms, molecules or ions
- number of moles= mass(g)/ Mr
Define relative formula mass.
The sum of of the relative atomic masses of the atoms in the number shown in the formula
Concentration of solutions(4):
Measured in mass per given volume of solution (g/dm cubed)
- the greater the mass the higher the concentration
- the greater the volume the lower the concentration
- concentration= mass(g)/ volume (dm cubed)
Dm cubed :
1 dm cubed = 1000 cm cubed
Chemical measurements(2):
Whenever a measurement is taken there is always a degree of uncertainty.
Degree of uncertainty= mean ± range /2
Limiting reactants(3):
The reactant that is completely used up, limits the amount of product that is made, less moles are made
Atom economy(3):
A measure of the amount of starting materials that end up as useful product
- high atom economy is important for sustainable development and economic reasons
Atom economy=
Mr of desired product/sum of Mr of all reactants
x100
Percentage yield(2):
It is comparing the amount of product as a percentage of the maximum theoretical amount
% yield= mass of product/ theoretical mass x 100
It is not always possible to obtain the calculated amount of a product because …(3)
- the reaction may not be reversible
- some of the products may be lost when it is separated from the reaction mixture
- some of the reactants may react in different ways to the expected reaction
How do you calculate the number of moles of a gas?
No. Of moles of a gas =
Volume of gas(dm cubed)/24dm cubed
What is concentration measured in?
Mol/dm cubed
Soluble salts(4):
They can be made from reacting acids with solid, insoluble substances
- add solid to acid until no more dissolves
- filter off excess solid
- crystallize to produce solid salts
Electrolysis(5):
The splitting up using electricity
- when an ionic compound is molten or it is dissolved in water ions are free to move
- these are then able to conduct electricity and are called electrolytes
- passing an electric current through electrolytes causes current through electrolyte which causes the ions to move through the electrodes
Anode(3):
- The positive electrode
- negative ions are attracted to it
- oxygen is formed at the anode
Cathode(4):
- the negative electrode
- positive ions are attracted to it
- metals will be produced at the cathode if it is less reactive then hydrogen
- hydrogen will be produced if the metal is more reactive than hydrogen
Strong acids
Are completely ionized in aqueous solutions
Weak acids
Only partially ionized in aqueous solution
Hydrogen ion concentration
As the pH decreases by 1 unit (becoming a stronger acid) the hydrogen ion concentration increases by 10
Cations
Cations are POSITIVE they move towards the negative cathode
Anions
Anions are NEGATIVE they move towards the positive anode
Acids in aqueous
They produce hydrogen ions
Alkalis in aqueous
Contain hydroxide ions
Extracting metals using electrolysis
The process is expensive due to the large amounts of energy required to produce the electrical current
dm3 to cm3 =
cm3 to dm3 =
dm3 to cm3 = x 1000
cm3 to dm3 = ÷ 1000
