3.1.2 AMOUNT OF SUBSTANCE

Question 1

What is the Mr of an atom relative to?

Answer 1

The mass of a carbon 12 isotope

Question 2

What is the definition of relative isotopic mass?

Answer 2

The mass of an atom of an isotope compared to 1/12th the mass of a C12 atom (Just mass number A)

Question 3

What is the definition of relative atomic mass

Answer 3

The weighted mean mass of an element compared to 1/12th of a C12 atom (Ar or Z)

• Takes into account that many elements are a mixture
  of isotopes

Question 4

What is the difference between relative formula mass and relative molecular mass?

Answer 4

Formula mass applies to ionic compounds, while molecular mass is for molecules (non metals)

Question 5

How do you calculate the empirical formula of a compound?

Answer 5

• Find the mass % of the elements in the compound. …
• Then change the % to grams. …
• Next, divide all the masses by their respective molar
  masses
• Pick the smallest answer of moles and divide all
  figures by that

Question 6

What is the ideal gas law?

Answer 6

PV = nRT, where R is the universal (perfect) gas constant

Question 7

What are the units for each variable in the ideal gas law?

Answer 7

Pressure - Pa or KPa
Volume - m^3 or cm^3
n - number of moles
R - J/K⋅mol
T - K

Question 8

How do you convert from Kelvin to degrees Celsius?

Answer 8

Add 273.15

Question 9

What assumptions are made when using the ideal gas equation?

Answer 9

• Gas molecules are tiny compared to the
  spaces between them
• Gas particle collisions are elastic
• No forces are acting between gas molecules
• Gas particles move randomly

Question 10

What is Boyle’s law?

Answer 10

pV = constant, as long as temperature is constant

p ∝ 1/V

Question 11

What is Charles’ law?

Answer 11

V/T = constant, as long as pressure is constant

V ∝ T

Question 12

What is Gay Lussac’s law?

Answer 12

p/T = constant, as long as volume is constant

p ∝ T

Question 13

What is room temperature in degrees celsius and kelvin?

Answer 13

25 °C, 298.15K