Chemistry - Online Multiple Choice Questions

1. What is the percentage composition of sulfur (molar mass 32.1 g/mol) in silver thiosulfate
   (Ag₂S₂O₃; molar mass 327.9 g/mol)
   1. 19.6
   2. 9.75
   3. 65.8
   4. 100
2. Which one of the following observations would not be evidence for a chemical reaction?
   1. Formation of a precipitate
   2. Evolution of a gas
   3. Melting of a solid
   4. Colour change
3. A gas cylinder X contains 0.20 mole of NO gas and another identical cylinder Y contains 0.15 mol of NO₂ gas. Which one of the following statements is correct?
   1. Y contains more molecules than X
   2. Y contains more atoms than X
   3. Y contains less atoms than X
   4. X and Y contain equal number of molecules
4. On heating, the hydrated salt CaSO₄.xH₂O loses its water of crystallization. In an experiment it was found that when 0.2 mol of the hydrated salt was heated 0.10 mol of water was lost. What is the molecular formula of the hydrated compound?
   1. CaSO₄
   2. CaSO₄.½H₂O
   3. CaSO₄.H₂O
   4. CaSO₄.2H₂O
5. A compound with the empirical formula of CH₂ is found to have a molar mass of 86 g/mol. Which one of the following best describes the molecular formula of the compound?
   1. C_6.1H_12.2
   2. C₆H₁₂
   3. CH₂
   4. C₈₆H₁₇₂
6. Propane burns in air according to the following equation

   C3H8

   +5O2

   3CO2

   + 4H2O

   A student burns 2.0 mol of propane (molar mass 44.0 g/mol) in excess oxygen. After collection of the products he finds he has 10.0 mol of water (molar mass 18.0 g/mol). The percentage yield of water is best described as
   1. More than what is possible
   2. Less than what is possible
   3. 20%
   4. 100%

Ans

1. 19.6
2. Melting of a solid
3. Y contains more atoms than X
4. CaSO₄.½H₂O
5. C₆H₁₂
6. _{More than what is possible}