Unit 3 - Quantitative Chemistry Flashcards
What is the law of conservation of mass?
The law of conservation of mass states that no atoms are lost or made
during a chemical reaction so the mass of the products equals the mass
of the reactants.
Write a balanced equation of magnesium reacting with hydrochloric
acid.
Mg(s) + 2 HCl(aq) → MgCl2(aq) + H2(g)
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, relative to 12C.
RFM - sum of RAM’s of all atoms in the formula.
The following reaction occurs in a test tube under a Bunsen
Burner:
4 MgO(s) + CH4(g) → 4 Mg(s) + 2 H2O(g) + CO2(g)
The carbon dioxide and water escape from the test tube.
Use the equation to explain why
They are both gases
What is Avogadro’s constant?
The number of atoms, molecules or ions in a mole of a given substance.
The value of the constant is 6.02 x 1023.
What is the formula that links mass, molecular mass and moles
together
Mass = Mr x Moles
What is the mass of 20 moles of calcium carbonate, CaCO3
Mass = Mr x Moles
Mr = 100
100 x 20 = 2000 g
Write down the two formulae that link concentration, mole/mass
and volume together.
Concentration (g per dm3) = Mass (g)/Volume (dm3)
Concentration (mol per dm3) = nr of moles/volume (dm3)
What is the molar volume of a gas at room
temperature and pressure?
1 mole of a gas at room temperature and pressure occupies 24 dm3
What is titration?
A technique for finding the concentration of a solution by reacting a known
volume of this solution with a solution of known concentration.
How do you conduct a titration?
a) Rinse the pipette with a solution of unknown concentration. Use the pipette to
measure out the known volume of this solution.
b) Add an indicator (a substance that changes colour at the end of titration)
c) Rinse the burette with a solution of known concentration. Discard the liquid.
Use a burette to gradually add the solution of a known concentration.
d) When indicator changes colour (at the end point), the volume added is
recorded
e) It is important to get concordant volume results - they have to lie close to each
other
f) Suitable calculations are performed to find the concentration.
Why is it not always possible to obtain the theoretical amount of product in
a chemical reaction?
● The 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 (side reactions may occur).
How is the percentage yield of a product in a chemical
reaction?
% Yield =
Actual mass of a product x 100%
/
Maximum theoretical mass of product
What is atom economy?
A measure of the amount of starting materials that end up as useful products.
It is a ratio of the relative formula mass of desired product to the sum of relative
formula masses of reactants.
