Moles

Question 1

Mole

Answer 1

The amount of any substance containing as many particles as there are in exactly 12g of the carbon - 12 isotope.

the number of particles in one mole is 6.02 x 10^23

number of particles = amount of substance (mol) x Avogadro constant

Question 2

Avogadro constant (NA)

Answer 2

The number of atoms per mole of the carbon - 12 isotope.

6.02 x 10^23

Question 3

Molar mass(M)

Answer 3

The mass of one mole

unit ~ g mol^-1

Question 4

Moles in a solid equation

Answer 4

number of moles (n) (mol) =

mass (m)(g) /molar mass (M) (g mol^-1)

Question 5

Avogadro constant calculations

Answer 5

number of particles = moles x avogadro constant

number of atoms = final answer x number of atoms. ( e.g NH3 has 3 atoms)

number of electrons = final answer x proton number

Question 6

Molecular formula

Answer 6

Tells us the element in a molecule and the number of atoms of each element.

A molecule consists of two or more atoms bonded together by covalent bonds.

Question 7

empirical formula

Answer 7

Tells us the simplest whole number ratio of the atoms of each element in a compound.

Question 8

Calculating empirical formulae

Answer 8

1. write down the elements and their masses underneath.
2. Caculate the moles of each element by dividing the mass by the mass number.
3. Divide each number by the smallest number of moles to find the simple ratio of the elements.
4. State the empirical formula ,EF

Question 9

Molecular formula calculation

Answer 9

MF= Molar mass / RFM of EF x EF

Question 10

Molar gas equation

Answer 10

moles of gas = volume ( dm^3) / 24 dm^3

1dm^3 = 1000cm^3

Question 11

what is the volume of one mole of a gas

Answer 11

1 mole of any gas , occupies a volume of 24000cm cubed or 24dm cubed at RTP ( room temperature and pressure)

1 mole = 24 dm^3

room temperature = 20 degrees
room pressure = 101kPa / 1atm

Question 12

The ideal gas equation

Answer 12

pV=nRT

p= pressure (Pa)
V= volume (m^3)
n = amount of gas molecules (mol)
R = ideal gas constant (8.314 J mol-1 K-1)
T = temperature (kelvin K)

Question 13

The assumptions made about the molecules in an ideal gas are :

Answer 13

• they are random in motion
• their collisions are elastic ~ no loss in kinetic energy)
• they are perfect spheres and negligible (small) in size.
• do not experience any intermolecular forces
• they exert pressure when they collide with each other and the walls of the container.
• their kinetic energy increase with temperature.

Question 14

conversions for the ideal gas equation

Answer 14

Volume :
1m^3 = 1000000 cm^3
1m^3 = 1000 dm^3

Pressure:
1KPa = 1000Pa
1atm = 101325 Pa

Temperature:
degrees Celsius to kelvin ~ add 273

Question 15

Calculating moles in solutions:

Answer 15

Moles (mol) =
volume (dm^3) x concentration (mol/dm^3 OR mol dm^-3)

1 dm^3 = 1000 cm^3

Question 16

Solutions

Answer 16

• formed when a solute is dissolved in a solvent.
• The concentration depends upon how much of a solute is dissolved in a volume of solvent.
• Dilute solution ~ contains a LOW number of solute per unit volume of the solvent (low concentration)
• Concentrated solution ~ contains a HIGH number of solute per unit volume of the solvent. (high concentration)

Question 17

Concentration

Answer 17

The amount of solute ,in mol , dissolved per 1dm^3

• A 1 molar solution is where one mole of a substance is dissolved in 1000cm^3 of water.
  (1M = 1 mol dm^-3)
• concentration can also be expressed in grams per dm^3 (g dm ^-3)

Question 18

Conversion of (mol dm ^-3) to (g dm^-3)

Answer 18

multiply the concentration value by the molar mass.
(mass = moles x molar mass)

Question 19

Stoichiometry & the three - step approach

Answer 19

• Refers to the MOLAR RELATONSHIP between the reactants and the products in a reaction.

1. Calculate the MOLES of the substance using the information in the question.

2.Using the MOLAR RATIO , deduce the moles of the substance being ASKED FOR.

3.Calculate the QUANTITY being asked for using the moles of the substance.