Topic 5 Formulae, Equation & Amounts of substance Flashcards
What is the ideal gas equation?
PV = nRT
P = Pressure (Pa) V = Volume (M^3) n = Amount of gas (Moles) R = Gas constant (8.31 J mol-1 K-1) T = Temperature (Kelvins - Celsius + 273)
What assumptions need to be made when using the ideal gas equation?
- Particles are not attracted to each other.
- Particles have no volume.
What is the equation for moles?
Moles = Mass / Mr
Mass is in grams
What is Avogadro’s constant?
6.02 x 10^23
What does Avogadro’s constant mean?
One mole of a substance is made up of 6.02 x 10^23 of those things. E.g. One mole of bananas is 6.02 x 10^23 bananas / One mole of oxygen is 6.02 x 10^23 atoms of oxygen.
What is a limiting reagent?
A limiting reagent is a reactant in a reaction that dictates how much product is formed.
What is the equation for % yield?
% yield =
Mass of product formed / Maximum theoretical mass
x 100
What is the equation for atom economy?
Atom economy = Mass of wanted product from equation / Total mass of products from equation x 100
What is the equation for concentration?
Concentration = Moles / Volume
or
Concentration = Mass / Volume
Conc = mol dm⁻³ (mol/dm³) Vol = dm³ Mass = g
How do you convert different volumes into m^3?
dm³ / 1000 = m³
cm³ / 1000000 = m³
How do you convert different units of pressure into Pa?
kPa x 1000 = Pa
MPa x 1000000 = Pa
1 atm of pressure = 100kPa
How do you convert degrees Celsius to Kelvins?
Celsius + 273 = Kelvins
How do you calculate back titrations?
Using the ratio of acid:alkali , calculate the moles of alkali that the acid reacts with (should tell you the moles of acid needed to neutralise) in the sample. Then calculate how many moles of alkali react in the resulting solution. Then calculate the final moles of unknown reactant (alkali should be in excess so: amount added - amount reacted = moles of unknown)
What is the definition of empirical formula?
Simplest ratio of each atom in each compound.
What is the definition of molecular formula?
The actual ratio of each atom in each compound.
How do you find the molecular formula from the empirical formula and formula mass?
Empirical formula x
(Formula mass (Mr) / Formula mass of empirical formula)
E.g. Empirical = CH2 Mr = 42 Mr of empirical = 14
42 / 14 = 3
CH2 x 3 = C3H6
What is the amount of a substance?
The physical quantity of a substance (n), measured in mol.
What is the relative atomic mass?
The average mass of an element relative to 1/12 the mass of an atom of the 12C isotope.
The values are relative so have no units.
What is the molar mass of a substance?
The mass of one mole of the chemical. The unit for this is g mol⁻¹.
What is the percentage composition?
The percentage by mass of each of the elements in the sample compound.
What is the species?
A collective noun used to refer generally to atoms, molecules or ions.
What are the gas laws?
The behaviour of gases and are summarised by the ideal gas equation.
What is an ideal gas?
A gas which obeys the ideal gas equation.
However, in practice real gases deviate to at least some extent from ideal behaviour.
What are SI units?
The internationally agreed units for measurement in science.
What is pressure?
The force per unit area. This is measured in pascals (Pa).
1 Pa is very small so pressure is often seen in kPa
1 atm = 100,000 Pa = 100 kPa
What is volume?
The amount of space taken up by a sample. This is generally measured in dm³.
1 dm³ = 1 litre
1 dm³ = 1000 cm³
1 m³ = 1000 dm³
1 m³ = 1000000 cm³
What is kelvin?
The SI unit for temperature on the absolute or kelvin temperature scale.
0K = absolute zero 273K = Freezing temp of water (0ᵒc) 373K = Boiling temp of water (100ᵒc)
What is the molar volume of a gas?
The volume of one mole of the gas under stated conditions.
At room temperature and atmospheric pressure, the molar volume of all gases is 24 dm³ mol⁻¹.
What is a titration?
A volumetric analysis technique for finding the concentrations of solutions and for the investigating the amounts of chemicals involved in reactions.
What is a standard solution?
A solution with an accurately known concentration.
What is a primary standard?
A chemical which can be weighed out accurately to make up a standard solution.
What is the end-point of a titration?
The point at which a colour change shows that enough of the solution in the burette has been added to react with the chemical in the conical flask.
What is the equivalence point of a titration?
The point at which the amount of reactant added from a burette is just enough to react exactly with all the measured amount of the chemical in the conical flask.
What is a strong acid?
An acid that is fully ionised when dissolved in water.
E.g. Hydrochloric Acid
What is a weak acid?
An acid that is only partially ionised when dissolved in water.
E.g. Ethanoic Acid
What is an accurate measurement?
A measurement that is precise and free from bias.
What are precise measurements?
Measurements that have values that are close together/concordant.
Precise measurements have a small random error.
What is bias in measurments?
This arises from systematic errors which affect all measurements in the same way, by making them all higher or lower than the true value.
What is yield?
The efficiency of a chemical process.
What is atom economy?
A measure of how efficiently a chemical reaction converts the atoms in its reactants to atoms in the product.
