C3 Quantitative Chem

Question 1

state the equation for relative atomic mass

Answer 1

(percentage of isotope1 x its mass) + (percentage of isotope2 x its mass)
/ 100

Question 2

state the equation for relative formula mass

Answer 2

(no. of atom1 x its relative atomic mass) + (no. of atom2 x its relative atomic mass)

Question 3

state the equation for percentage by mass of a compound

Answer 3

(no. of atom1 x its relative atomic mass) / total relative formula mass of compound
x 100

Question 4

state the equation linking moles, mass, and relative formula mass

Answer 4

mass = Mr x moles
moles = mass / Mr

Question 5

state the Avogadro constant

Answer 5

6.022 x 10²³
one mole of any substance will have the same number of particles

Question 6

define a mole

Answer 6

• the relative formula mass in grams
• applies to atoms, molecules, ions, electrons

Question 7

state the equation for concentration of a solution

Answer 7

concentration = mass of solute / volume of entire solvent
(g/dm³) (g) (dm³)

Question 8

state why whenever a measurement is made there is always some uncertainty about the result

Answer 8

• random error
• limited resolution of instruments used
• uncertainty of a mean result can be calculated using
  uncertainty = (range/2)
• uncertainty can be reduced by: repeating experiments, testing more samples
• you can have more confidence in results with a smaller uncertainty
• results with a smaller range are more precise