Concepts of Moles and molar mass problem The number of molecules in a drop of wa

Question

Concepts of Moles and molar mass problem The number of molecules in a drop of water that has a mass of 0.0500 g is A. 2.17 times 10^26 molecules H_2O B. 6.50 times 10^26 molecules H_2O C. 1.67 times 10^21 molecules H_2O D. 5.02 times 10^21 molecules H_2O E. 5.42 times 10^23 molecules H_2O In comparing 1 mole of carbon atoms to one mole of magnesium atoms, which statement is TRUE? A) The mass of 1 of carbon is greater than the mass of 1 mole of magnesium. B) The mass of 1 mole of magnesium is greater than the mass of 1 mole of carbon. C) The mass of 1 mole of carbon is the same as mass of 1 mole of magnesium. D) There are more atoms in 1 mole of magnesium than in 1 mole of carbon. E) None (A-D) of the above

Explanation / Answer

1)

mass of H2O = 0.0500 g

molar mass of H2O = 18 g/mol

number of mol of H2O = mass/ molar mass

= 0.0500/18

= 2.778*10^-3 mol

number of molecules = number of moles * Avogadro’s number

= 2.778*10^-3 * 6.022*10^23

= 1.67*10^21 molecules

Answer: C

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