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Chemistry µIB
1.2b Empirical + Molecular Formulae
10 quick questions



10 minutes maximum!

An IB Periodic Table is required. Calculators should not be used!


1. A sample of an oxide of sulfur was analysed and found to contain 1.6g of sulfur and 2.4g of oxygen. What is its empirical formula?

  • A.   S2O3
  • B.   SO3
  • C.   SO2
  • D.   S2O
2. Metal X forms an oxide which contains 32% by mass of oxygen. Metal X has a relative atomic mass of 51. What is the empirical formula of the oxide?
  • A.   XO2
  • B.   X2O
  • C.   XO3
  • D.   X2O3

3. What is the empirical formula of a compound containing 79.9% by mass of carbon and 20.1% by mass of hydrogen?

  • A.   CH2
  • B.   CH3
  • C.   CH4
  • D.   C2H3
4. Melamine has an empirical formula of CH2N2 and its molecular mass is 126 g mol-1. What is the molecular formula of melamine? melamine plates and bowl
Dwight Burdette
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  • A.   CH2N2
  • B.   C2H4N4
  • C.   C3H6N6
  • D.   C4H8N5
5. 5.0g of an oxide of chromium was formed from 2.6g of chromium. What is the empirical formula of this oxide?
  • A.   CrO
  • B.   CrO3
  • C.   CrO6
  • D.   Cr2O3

6. Which of the following compounds has/have the empirical formula CH2O?

I. C6H12O6
III. C12H24O11
  • A.   I only
  • B.   I and II only
  • C.   II and III only
  • D.   I, II and III
7. 4.80g of element Y combines with exactly 1.60g of oxygen to form a compound of formula Y2O. What is the relative atomic mass of Y?
  • A.   24.0
  • B.   32.0
  • C.   48.0
  • D.   64.0
8. How many moles of water of crystallization are combined with each mole of calcium sulfate if 2.72g of anhydrous calcium sulfate (Mr = 136g mol-1) is formed when 3.44g of hydrated calcium sulfate is heated to constant mass?
  • A.   1
  • B.   2
  • C.   3
  • D.   4
9. What is the empirical formula of a hydrocarbon which produced 4.40g of carbon dioxide and 2.70g of water on complete combustion?
  • A.   CH
  • B.   CH2
  • C.   CH3
  • D.   C2H3
10. Which of the following compounds, used in the production of fertilizers, has the highest percentage by mass of nitrogen? bags of fertiliser
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  • A.   NH3
  • B.   NH4NO3
  • C.   CO(NH2)2
  • D.   (NH4)2SO4