igcse chemistry question/answers

CAIE Chemistry IGCSE: 3.2 Relative Masses of Atoms and Molecules
Flashcards


Define relative atomic mass (ArA_r):

The relative atomic mass (ArA_r) of an element is the average mass of the isotopes of an
element compared to 112\frac{1}{12} of the mass of an atom of carbon-12.



Give the relative atomic mass (ArA_r) for chlorine:

The ArA_r for chlorine is 35.5.



What does the term relative formula mass (MrM_r) mean?

The relative formula mass is the sum of the relative atomic masses of atoms in a formula unit. It
is used for giant ionic structures.



Give the relative formula mass for sodium chloride (NaCl):

● MrM_r of NaCl:
○ ArA_r of Na = 23
○ ArA_r of Cl = 35.5
○ MrM_r of NaCl = 23+35.5=58.523 + 35.5 = 58.5



What does the term relative molecular mass (MrM_r) mean?

The relative molecular mass is the sum of the relative atomic masses of atoms in a molecule.



Give the relative molecular mass (MrM_r) of calcium carbonate (CaCO3_3):

● MrM_r of CaCO3_3:
○ ArA_r of Ca = 40
○ ArA_r of C = 12
○ ArA_r of O = 16 (multiplied by 3)
○ MrM_r of CaCO3_3 = 40+12+(16×3)=10040 + 12 + (16 \times 3) = 100