Topic 3-Quantitative Chemistry Flashcards
What is the law of conservation?
No atoms are lost or made during a chemical reaction so the mass of the products=mass of the reactants
Define relative atomic mass and relative formula mass
RAM - average mass of atoms in an element taking into account masses and abundance of its isotopes
RFM - sum of RAM’s of all atoms in the formula
What is Avogadro’s constant?
6.02 x 10^23
What is the formula that links mass, molecular mass and moles together?
Mass=Mr x Moles
State what we mean by a limiting reactant in a chemical reaction
In a chemical reaction involving two reactants, it is common to use an excess of one of the reactants to ensure that all of the other reactant is used.
The reactant that is completely used up is called the limiting reactant because it limits the amount of products
Write down the two formulae that link concentration, mass and volume together
conc (g per dm^3) = mass (g)/volume (dm^3)
conc (mol per dm^3) = nr of moles/volume (dm^3)
What is the molar volume of a gas at room temperature and pressure?
1 mole of gas at room temp and pressure occupies 24dm^3
What is the formula for percentage yield?
PY=Amount of product produced/maximum amount of product possible x 100
Why might it not always be possible to obtain the calculated amount of a product?
Reaction may not go to completion because it is reversible
Some of the product may be lost when it is separated from the reaction mixture
Some of the reactants may react in ways different to the expected reaction
What is atom economy?
A measure of the amount of starting materials that end up as useful products
It is important for sustainable development and for economic reasons to use reaction with high atom economy
What is the formula for atom economy?
(Mr of desired product from reaction / sum of Mr of all reactants) x 100
Why might a particular reaction pathway be chosen/not chosen?
Atom economy
Yield
Rate
Equilibrium position
Usefulness of by-products
How do you calculate moles of a gas produced if the reaction is at room temp?
Volume of gas (dm^3) at RTP = moles x 24
What is titration?
A technique for finding the conc of a solution by reacting a known volume of this solution with a solution of known concentration
How do you conduct a titration?
Rinse the pipette with a solution of unknown concentration. Use the pipette to measure out the known volume of this solution
Add an indicator
Rinse the burette with a solution of known concentration. Discard the liquid and use the burette to gradually add the solution of a known concentration
When indicator changes colour (at the end point), the volume added is recorded
It is important to get concordant volume results - they have to lie close to each other
Suitable calculations are performed to find the concentration
