general knowledge 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.
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.
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 10^23
What is atom economy?
A measure of the amount of starting materials that end up as useful products.
It is a ratio of the Mr of desired product to the sum of the Mr of reactants.
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
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.
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
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.
In more detail, what is the relative formula mass?
Also known as Mr
sum of relative atomic masses of atoms in the elements in a formula
never involves big numbers in front of equation
Why is it not always possible to achieve 100% percentage yield in a chemical reaction?
some product may be lost when it’s separated from the reaction mixture
some reactants may react in different ways to the expected reaction; therefore we dont get the product we expect
reversible reactions may not go to completion.
How does the mass of a solute and volume of a solution affect the concentration
- if the mass of the solute is increased and the volume of the solution remains the same, the concentration increases
- if the volume of the solution is increased and the mass of the solute remains the same, the concentration decreases
why is atom economy important?
- minimising the production of unwanted product, saves money
- incr sustainability by not wasting materials.
