2.1.3: Amount of substance Flashcards
What is an empirical formula?
Simplest whole number ratio of atoms of each element present in a compound
How to calculate empirical formula
● Divide the amount of each element by its molar mass
● Divide the answers by the smallest value obtained
● If there is a decimal, divide by a suitable number to make it into a whole number
What is the unit used to measure amount of substance?
Mole
What does the Avogadro constant represent?
The number of atoms per mole of the carbon-12 isotope
How to calculate the mass of 1 mole of the element?
Mass of 1 mole = relative atomic mass in grams
How to calculate moles when mass and molar mass (mr) are given?
Moles (mol) = mass (g) / molar mass (mr) (g mol -1)
State Avogadro’s law
Under the same temperature and pressure, one mole of any gas would occupy the same volume.
How much volume does a gas occupy, at room temperature and
pressure?
24 dm3 or 24000 cm3
Define molar gas volume
The volume per mole of gas molecules
Why do different gas particles occupy the same volume?
The gas particles are very spread out,
hence individual differences has no
effect.
How to calculate moles when gas volume is given?
Moles (mol) = volume (dm3) / 24
Moles (mol) = volume (cm3) / 24000
What are the ideal ways in which gases behave?
● They are in continuous motion
● No intermolecular forces experienced
● Exert pressure when they collide with each other or
container
● No kinetic energy is lost in the collisions
● When temperature increases, kinetic energy of gases also increase
Write down the ideal gas equation (in words and symbols, including the units?
pV = nRT
Pressure (Pa) x volume (m3) = number of
moles (mol) x gas constant (8.314 J/mol-1)x temperature (K)
1 atmospheric pressure is equal to how many pascal?
1 atm = 101325 Pa
0℃ is equal to how many kelvin?
273 K
What does concentration of a solution mean?
It is the amount of solute dissolved in 1
dm3 of solvent
How do you calculate moles when concentration and volume are
given?
Moles (mol) = concentration (mol dm-3) x
volume (dm3)
What is a standard solution?
A solution of known concentration
Write down the steps to prepare a standard solution
- Weigh the solute using the weigh by difference method
- In a beaker dissolve the solute using the solvent
- Pour the solution into a volumetric flask
- Rinse the beaker using the solution and add it to the flask
- Add solvent to the flask carefully until it reaches the graduation line
- Mix the solution thoroughly to ensure complete mixing
What does the terms concentrated and dilute mean?
Concentrated - large amount of solute per dm3 of solvent
Dilute - small amount of solute per dm3 of solvent
What is a species in a chemical reaction?
Any particle that takes part in a reaction
What does percentage yield mean?
The efficiency of which reactants are
converted into products
What are the reasons for not obtaining 100% yield? (5 marks)
● Reaction may be at equilibrium
● The reactants may be impure
● Side reactions could happen
● Reactants or products may be left behind while
transferring
● Loss of products during separation and purification
How is percentage yield calculated?
Percentage yield = (actual amount of product (mol) / theoretical amount of product (mol)) x 100
What does atom economy tell us about?
The proportion of desired products
compared with all the products formed in
the reaction
How is atom economy calculated?
Atom economy = (molecular mass of desired product / sum of the molecular masses of all products) x 100
Does 100% yield mean 100% atom economy?
No, even if all the reactants are converted into products, not all products of the reaction will be the required products
Which type of reaction has 100% atom economy?
Addition reactions (two or more reactants are combined to form a product)
