Module 2: Atoms and reactions

Question 1

What is relative atomic mass?

Answer 1

Relative atomic mass is the average mass per atom of the naturally occurring form of an element relative to 1/12th of the mass of a carbon-12 atom.

Question 2

What is relative isotopic mass?

Answer 2

Relative isotopic mass is the mass of an atom of an isotope relative to 1/12th of the mass of a carbon-12 atom.

Question 3

What is relative molecular mass?

Answer 3

Relative molecular mass is the sum of the relative atomic masses of the constituent atoms of a molecule relative to 1/12th of the mass of a carbon-12 atom.

Question 4

What is the equation for calculating the relative atomic mass (Ar) of an isotope?

Answer 4

Ar = ( { abundance of isotope x isotopic mass of isotope ) /100

Question 5

What is the equation linking molar mass, mass and number of moles?

Answer 5

number of moles = mass (g) / Mr (g/mol)

Question 6

What is meant by the molar mass?

Answer 6

The mass per mole of a substance

Question 7

What number represents Avogadro’s constant?

Answer 7

6.02 x 10*23

Question 8

What is the empirical formula?

Answer 8

The empirical formula is the formula showing the simplest whole number ratio of atoms of each element present in a compound.

Question 9

What is the molecular formula?

Answer 9

The molecular formula is the formula showing the actual number of atoms of each element in a molecule.

Question 10

What is stated by Avogadro’s law?

Answer 10

At the same temperature and pressure, 1 mole of any gas will occupy the same volume.

Question 11

What is standard temperature and pressure?

Answer 11

Pressure = 1 Atmosphere = 100,000Pa
Temperature = 25*C = 298 K

Question 12

What is the equation for number of moles using volume (in dm cubed and cm cubed) at RTP?

Answer 12

number of moles = volume (dm cubed) / 24

number of moles = volume (cm cubed) / 24000

Question 13

What is the ideal gas equation?

Answer 13

PV = nRT

P = pressure in Pa
V = volume in m cubed
dm cubed / 103 = m cubed
cm cubed /106 = m cubed
n = number of moles
R = universal gas constant = 8.314 Jmol-1K-1
T = temperature in K
T(K) = T(*C) + 273

Question 14

What does the % yield of a chemical reaction show?

Answer 14

The % yield of a chemical reaction shows how much product was actually made compared with the amount of product the was expected

Question 15

What is the equation for % yield?

Answer 15

% yield = actual yield (g) / theoretical yield (g) x 100

Question 16

What are some reasons as to why yield is not often 100%?

Answer 16

• the reaction may be incomplete
• side reactions may occur, leading to by-products
• reactants may not be pure
• some reactants/products may be left behind in the apparatus

Question 17

What is atom economy?

Answer 17

Atom economy is the % of reactants that end up as useful products

Question 18

What is the equation for atom economy?

Answer 18

Atom economy = mass of wanted product (s) / total mass of all products x 100

Question 19

What is the equation linking concentration, moles and volume?

Answer 19

Conc. (moles.dm-3) = moles / volume (dm3)

Question 20

What is concentration?

Answer 20

A measure of how much solute is dissolved per solvent.

Question 21

What is meant by hydrated?

Answer 21

Hydrated refers to a crystalline compound containing water molecules.

Question 22

What is meant by anhydrous?

Answer 22

Anhydrous refers to a substance that contains no water molecules.

Question 23

What is water of crystallisation?

Answer 23

Water molecules that are within the crystalline structure of the compound.