9.3 Stoichiometry Flashcards
How do you find the relative atomic mass? [2]
(percentage x mass) + (percentage x mass) /100
How do you find the relative molecular mass? [2]
Atomic mass x how many there are , added together
e.g. CaCO₃
Ca = 40.0 x 1 = 40.0
C = 12.0 x 1 = 12.0
O = 16.0 x 3 = 48.0
40 + 12 + 48 = 100
MrCaCO₃ = 100.0
What is the definition of relative atomic mass, Ar? [2]
The average mass of the isotopes of an element compared to 1/12th of the mass of an atom of 12C.
What is the definition of relative molecular mass, Mr? [2]
The sum of the relative atomic masses.
What is the Law of Conservation of Mass? [1]
Mass is neither created nor destroyed.
How do you find the percent purity of a substance? [2]
total mass x100
What is the mole number aka Avogadro’s constant? [2]
6.02 x 10-to the power of 23
Formula for number of moles? [2]
mass (of substance) / relative molecular mass
Symbol formula for number of moles? [2]
n(mol) = m (g) / Mr (g/mol)
How many grams of carbon is 6.02x10-to the power of 23 atoms? [1]
12g
What is the formula for the amount of atoms/molecules present? [2]
number of moles x avogadro constant (6.02x10-to the power of 23)
When do we use moles? [2]
- Covalent molecules
- Ionic compounds
What is the formula for the concentration of moles (for liquids and gases)? [2]
amount of substance / volume
units = g/cm3 or kg/dm3
What is the gas test for HYDROGEN? [2]
lit splint + hydrogen = squeaky pop
What is the gas test for OXYGEN? [2]
lit splint + oxygen = blow it out and it’s still glowing
- oxygen will relight a glowing splint
