Molecular mass of water (18g) means__________________?
Correct answer: D. all
- A. 1-mole molecules of water
- B. 1-gram molecule of water
- C. 3-gram atoms
- D. all
Explanation
The molar mass of water is 2 x 1 + 16 = 18 g mol^-1, so 18 g of water is 1 mol of H2O molecules and is also called 1 gram-molecule. Each water molecule contains two hydrogen atoms and one oxygen atom, so one mole contains 3 gram-atoms in total. Students may choose a or b alone, but both describe the same 18 g amount and c is also true in the older terminology.
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About Moles and Avogadro's Number
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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