✅5 - Formulae, Equations and Amounts of Substance Flashcards
What are amounts of substance measured in?
Moles (mol)
What does one mole contain?
A standard number of atoms, molecules or ions
What is the relative atom mass?
The average mass d an element relative to 1/12th if the mass of an atom of carbon12.
What is molar mass?
The mass of one mole of a chemical with the unit g mol-1.
How would you work out the molar mass of a molecule?
Add up the relative atomic masses of all the atoms in the molecule
How do you work out the amount of substance in moles?
mass of substance(g) / molar mass (g mol-1)
What is a species?
A collective noun to refer generally to atoms, molecules or ions
What is the Avogadro constant?
The number of atoms, molecules or ions in one mole of a substance. 6.02 x 10^23 mol-1
How would you work out the number of atoms, molecules or formula units?
amount of chemical (moles) x Avogadro constant (mol-1)
What is the empirical formula?
The simplest whole number ratio of the atoms of different elements in a compound
How would you work out the empirical formula?
- Write down the actual mass of each element
- Write down the molar mass of each element
- Divide the actual mass by the molar mass for each element
- Divide all the numbers by the smallest one
- See ratio
What is molecular formula?
The total number of atoms of each element in the molecule
What is percentage composition?
The percentage by mass of each of the elements in a sample of a compound
How would you work out the empirical formula from percentages?
Turn each percentage into grams and assume the total mass of the compound is 100g
What is the ideal gas equation?
pV = nRT
1 atmosphere =
101,325 Pa
1 bar =
100k Pa (100,000Pa)
To convert °C into K…
… +273 to the number
To convert K into °C
Take away 273 from the number
1m^3 =
1000dm^3 (1,000,000cm^3)
R=
8.31JK-1mol-1
What most the units be in the ideal gas equation?
P = Pa V = m^3 n = moles T = Kelvin
The gas laws state that the volume of a gas depends on what three things?
- The temperature
- The pressure
- The amount of gas in moles
What could the ideal gas equation be used for?
Measuring the molar masses of gases in the days before mass spectrometry
What is the ideal gas equation accurate enough to determine?
The molecular formula of elements and compounds
How is the molecular formula found from the ideal gas equation?
- A weighted sample of a liquid is injected into a syringe heated in an oven
- Measurements are taken of the volume of vapour, the temperature and its pressure
- They are then converted into SI units and put into the ideal gas equation to find the number of moles
What is the molar volume of a gas?
The volume of 1mol of the gas under stated conditions. At room temperature and atmospheric pressure the molar volume of all gases is 24dm-3mol-1
What is room temperature?
16°C
What is atmospheric pressure?
100kPa
Volume of gas (cm3) =
Amount of gas (mol) x molar volume (cm3 mol-1)
How would led you calculate the amounts of reactants and products?
- Write the balanced equation for the reaction
- Write down the amount in moles of the relevant reactants and products according to the ratio in the equation
- Convert the amount in moles into masses of the reactants and products
- Scale the masses to the quantities required
The volume of gas, under a given temperature and pressure depends only on…
…the amount of gas, not the type of gas
Concentration (g/dm-3) =
Mass of solute (g) / volume of solution (dm-3)
Concentration (mol/dm-3) =
Amount of solute (mol) / volume of solution (dm3)
What is the concentration of a solution?
How much solute is dissolved in a certain volume
What is a titration?
A volumetric analysis technique for finding the concentrations of solutions and for investigation 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 with can be weighed out accurately to make up a standard solution
The method for preparing a standard solution is only appropriate with a chemical this is…
- is very pure
- does not gain or loss mass when in the air
- has a relatively high molar mass so that weighing errors are minimised
What was the ideal gas equation used for?
Measuring the molar masses of gases before mass spectrometry
What is the ideal gas equation accurate enough to determine?
The molecular formula of elements and compounds
What does the ideal gas equation show?
That at a fixed temperature and pressure the volume of a gas depends only
on the amount of moles.
How do you calculate the masses of reactants and products?
- Write a balanced equation
- Write down the amounts in moles of the relevant reactants and products in the equation
- Convert these amounts in moles of the relevant reactants and products into masses
- Scale to the quantities required
What is an uncertainty?
The amount of error your measurements might have?
For any piece of equipment, what will the uncertainty be?
Half the smallest increment of measure in either direction
What should be done if different measurements are being combined?
Their uncertainties should be combined
How would you calculate percentage uncertainty?
Uncertainty/reading x 100
How can uncertainty be reduced?
By using the most precise equipment possible and the largest measurements
What is theoretical yield?
The maximum that you could get
How would you calculate theoretical yield?
Using the moles of reactants and products
How would you calculate percentage yield?
Actual yield/theoretical yield x 100
What is atom economy?
A measure of how efficient the reaction is
How would you calculate atom economy?
Molar mass of desired product/combined molar masses of all products x 100
