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.
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?
6.02 x 10^23
The number of atoms, molecules or ions in a mole of a given substance
What is the formula that links mass, molecular mass and moles together?
Mass (g) = 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.
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.
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’s a ratio of the relative formula mass of desired product to the sum of relative formula masses of reactants
What is a balanced symbol equation?
A symbol equation in which there are equal numbers of each type of atom on either side of the equation
Why does mass decrease in a reaction?
A new gas is formed
Why does mass increase in a reaction?
A reactant is a gas
What is a coefficient?
Big numbers in front of a formulae which multiply a formula
What is the theoretical yield?
The maximum amount of product than can be made
What is the actual yield?
The amount of product made by carrying out the reaction
What is a reversible reaction?
A chemical reaction in which the product re-form the original reactants
Why is the % yield less than 100%?
- reversible reaction
- product is lost
- side reactions
What are side reactions?
Reactions that don’t give the desired product of a reaction
What is the formula for atom economy?
Formula mass of desired product / formula mass of all reactants x 100
What is 100% of atom economy?
All the atoms in the reactant have been turned into useful products
What could you do to improve atom economy?
- use a better reaction
- sell side products
What is the standard solution?
A solution of known concentration
What is a burette?
A graduated glass tube with a tap at one end, for delivering known volumes of a liquid
What is a pipette?
A glass or plastic tube used to accurately measure liquid
What is a meniscus?
Curved surface of liquid
What is the indicator?
A compound that changes colour in the presence of an acid or a base
What is a white tile?
A white surface to clearly see the indicator changing colour
What is a conical flask?
Uses to hold liquids, narrow neck to prevent splashes
