1.2 Amount of Substance Flashcards
What is the symbol for amount of substance?
n
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 is the mass of 1 mole of the element calculated?
Mass of 1 mole = relative atomic mass in grams
How are the moles when mass and molar mass are given calculated?
Moles (mol) = mass (g) / molar mass (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
Or
Moles (mol) = volume (cm3) / 24000
What are the ideal ways in which gases behave?
5
● 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?
273K
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)
● 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
