The number of oxygen in 0.5 mole of AI2 (CO3)3 is:
Correct answer: C. 2.7 x 10^24
- A. 4.5 x 10^23
- B. 3.6 x 10^24
- C. 2.7 x 10^24
- D. 9.0 x 10^23
Explanation
In one molecule of aluminum carbonate, there are 3 molecules of carbonate ions, which have 3 oxygen atoms each so there are 9 atoms of oxygen in 1 molecule of aluminum carbonate. Therefore in 0.5 moles of aluminum carbonate, there are 0.5NA particles of aluminum carbonate which means there are 9 * 0.5NA = 4.5 NA particles of oxygen. 1 NA = 6.02 x 1023 so 4.5 NA = 4.5 x 6.02 x 1023 = 27 x 1023 = 2.7 x 1024 atoms of oxygen. Hence, C is the correct answer.
This question appeared on the ETEA MDCAT 2005 paper, which you can sit online with every answer explained.
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The mole connects the microscopic number of particles with measurable mass, using Avogadro's number, 6.022 × 10²³ particles per mole. Questions involve molar mass, conversion between mass, moles and particles, percentage composition, empirical and molecular formulas, and distinguishing atoms, molecules, ions and formula units.
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