Quantitative Chemistry - done Flashcards
What is the Law of Conservation of Mass?
No matter is lost or gained during a chemical reaction.
How to find the Mr?
All the relative atomic masses (Ar) of all the atoms in the molecular formula added together
What is the avogadro constant?
one mole of a substance contains the Avogadro constant number of particles. contains 6.02 x 10^23
What is the equation that links moles, mass and mr?
mass = moles * Mr
How to find the % mass?
% mass = ( n x Ar / Mr ) * 100
What is the limiting reagents/reactant?
Reactants that get used up first in a reaction is the limiting reactant/reagent
What is the yield of a reaction?
The mass of the product that a chemical reaction produced
What does percentage yield do?
Compares the mass of the product that the reaction ACTUALLY produced with the maximum theoretical mass that could possibly be produced
How to find % yield?
Percentage yield = ( Actual mass of products / Maximum theoretical mass of products ) * 100
Factors affecting percentage yield: (5)
o Reversible reactions - as products form they react to re-form reactants again
o Reactants may react to give unexpected/unwanted products
o Some of the product may be lost in handling or left in apparatus
o Reactants may not be pure
o Some of the desired products may be lost in separation from the reaction mixture
What is atom economy?
The measure of the extent to which the atoms in the starting materials end up in the desired product
How to find % atom economy?
% atom economy = ( Mr of desired product / Sum of Mr’s of ALL reactants )
* 100
How to complete titration?
- Use the pipette and pipette filler to put the acid into the conical flask
- Stand the conical flask on a white tile
- Clamp the burette vertically in the clamp stand. There should be just enough room underneath for the conical flask and tile
- Make sure the burette tap is closed and use as small funnel to carefully fill the burette with the acid slightly above the Ocm3 line.
- Then open the tap to fill the jet, then take the initial reading of the burette to 2d.p
- Put 5-10 drops of phenolphthalein indicator into the conical flask. Swirl and mix
- Carefully open the tap to the acid flows into the flask at a drop by drop rate
- Constantly swirl the flask when adding the acid
- When there is a sudden colour change, it is the end point of the reaction.
- Read the burette scale carefully to 2d.p and record the volume of acid you added
Why use a white tile in titration?
allows for you to see the colour change clearly
What is phenolphthalein in acid?
pink
