T3 quantitative chemistry

Question 1

law of conservation of mass

Answer 1

no atoms are lost or made during a chemical reaction so the mass of the products equals the mass of the reactants

Question 2

define relative atomic mass and relative formula mass

Answer 2

RAM - average mass of atoms in an element taking into account masses and abundance of its isotopes

RFM - sum of all RAM’s of all atoms in the formula

Question 3

what is Avogadro’s constant

Answer 3

number of atoms, molecules or ions in a mole of a given substance

6.02x10^23

Question 4

formula linking mass, molecular mass and moles together

Answer 4

mass = Mr x moles

Question 5

what is meant by a limiting reactant in a chemical reaction

Answer 5

in a chemical reaction involving two reactants, common to use an excess of one of the reactants to ensure that all of the other reactant is used

reactant that is completely used up is called the limiting reactant because it limits the amount of products

Question 6

two formulae that links concentration, mass and volume together

Answer 6

concentration (g per dm3) = mass(g) / volume(dm3)

concentration (mol per dm3) = nr of moles / volume (dm3)

Question 7

what is the molar volume of a gas at room temperature and pressure

Answer 7

1 mole of a gas at room temperature and pressure occupies 24dm3

Question 8

what is titration

Answer 8

technique for finding the concentration of a solution by reacting a known volume of this solution with a solution of known concentration

Question 9

how do you conduct titration

Answer 9

1. rinse the pipette with a solution of unknown concentration, use the pipette to measure out the known volume of this solution
2. add an indicator (substance that changes colour at the end )
3. rinse the burette with a solution of known concentration, discard the liquid, use a burette to gradually add the solution of a known concentration
4. when indicator changes colour, volume added is recorded
5. important to get concordant volume results, have to lie close to each other
6. suitable calculations are performed to find the concentration

Question 10

why is it not always possible to obtain the theoretical amount of product in a chemical reaction

Answer 10

reaction may not go to completion because it’s 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)

Question 11

percentage yield equation

Answer 11

percentage yield = (actual yield / theoretical yield) x100

Question 12

what is atom economy

Answer 12

measure of the atom of starting materials that ends up as useful products

ratio of the relative formula mass of desired product to the sum of relative formula masses of reactants

Question 13

atom economy equation

Answer 13

total Mr of desired product / total Mr of all reactants