Chapter 3 - Amount of substance Flashcards
What is the amount of substance ?
A quantity (n) used to count the number of particles in a substance
What is a mole ?
The amount of any substance that contains 6.02x10^23 particles
What is avogadros constant ?
- Avogadro’s constant is 6.02x10^23
- It is the number of particles in each mole of carbon-12
What is molar mass (Mr) ?
Molar mass gives the mass in grams in each mole of the substance
What equation links molar mass, mass and amount ?
- n = m÷Mr
- n - number of moles (mol)
- m - mass (g)
- Mr - molar mass (g/mol)
How do you work out the amount of particles ?
(m÷Mr) x avogadros constant
How do you work out how many atoms there are ?
Add together all the atoms and then multiply by avogadros constant
What is the molecular formula ?
The number of atoms of each element in a molecule.
What is the empirical formula ?
The simplest whole-number ratio of atoms of each element in a compound.
What is relative molecular mass?
The mass of a molecule compared with the mass of an atom of carbon-12.
How do you calculate relative molecular mass ?
Worked out by adding together the relative atomic masses of the elements making up a molecule
What is relative formula mass ?
It compares the mass of a formula unit with the mass of an atom of carbon-12
How do you calculate the relative formula mass ?
It is calculated by adding together the relative atomic masses of the elements in the empirical formula
How do you work out molecular formula from composition by mass ?
- Use the mass and mr to find out the number of moles
- Then use the ratio of moles to work out how many molecules there are of each element
How do you work out molecular formula from composition by percentage ?
- Use the mass (percentage) and mr to find out the number of moles
- Then use the ratio of moles to work out how many molecules there are of each element
In hydrated salts, what is the name given to water molecules?
Water of crystallisation
What is the concentration of a solute ?
The amount of solute dissolved in a solution
What is the equation for finding a solutions concentration ?
- n =cv
n - number of moles (mol)
c - concentration (mol/dm^3)
v - volume (dm^3)
How do you get from mol/dm^3 to g/dm^3 ?
You multiply it by the mr
What is a standard solution ?
A solution of known concentration
How is it prepared ?
Dissolving an exact mass of the solute in a solvent and making up the solution to an exact volume
What is molar gas volume ?
The volume per mole of gas molecules at RTP
What is the value of molar gas volume at RTP ?
24 dm^3/mol
What are the conditions of RTP ?
- 20 degrees
- 101 kPa (1 atm)
What is the equation for molar gas volume ?
- n = v/mgv
n - number of moles (mol)
v - volume (dm^3)
mgv - molar gas volume (dm^3/mol)
What are the assumptions made about an ideal gas ?
- Random Motion
- Elastic collisions
- Negligible size
- No IMFs
What is the equation for the ideal gas law ?
pV = nRT
What is the value of the ideal gas constant ?
8.314 J/mol/K
What are the standard conditions ?
The standard conditions are 298K and 100kPa
cm3 to m3
x 10^-6
dm3 to m3
- x 10^-3
degrees C to K
+ 273
KPa to Pa
x 10^3
What is stoichiometry?
The balancing numbers that give us the moles of each substance in a balanced equation
What are balanced equations used to find ?
- The quantities of reactants required to prepare a required quantity of a product.
- The quantities of products formed
What is the actual yield ?
The actual amount of product that you get
What is the theoretical yield ?
The maximum possible amount of product
What is the percentage yield ?
The actual yield divided by the theoretical yield expressed as a percentage.
Why is the theoretical yield so hard to achieve ?
- The reaction can be incomplete
- Side reactions can give off different products
- There can be a loss of product when handling the substance or during purification
- The reaction could be reversible
What is the limiting reagent ?
- The reactant that is not in excess
- Limits the reaction
How can it be worked out ?
Can be worked out by working out the amount in moles of each reactant and comparing that with the equation
What is atom economy ?
Atom economy is a measure of how well atoms have been utilised
How do you work out atom economy ?
The mr of desired products divided by the mr of all products, expressed as a percentage.
What are the benefits of a high atom economy ?
- Produce a larger proportion of desired products and few waste products.
- Important for sustainability, the best use of natural resources.
