Ex 3:a) Find the mass of 2.5 moles of NaCl.b) Find the number of molecules in 15 g of hydrochloric acid.c) How many atoms in 6.6 moles of Aluminium oxide.(Careful, there are 5 atoms in one formula unit ofaluminium oxide.)d) How many hydrogen atoms in 7.0 g of water?
Question
Ex 3:a) Find the mass of 2.5 moles of NaCl.b) Find the number of molecules in 15 g of hydrochloric acid.c) How many atoms in 6.6 moles of Aluminium oxide.(Careful, there are 5 atoms in one formula unit ofaluminium oxide.)d) How many hydrogen atoms in 7.0 g of water?
Solution
a) The molar mass of NaCl (Sodium Chloride) is approximately 58.44 g/mol. Therefore, the mass of 2.5 moles of NaCl can be calculated as follows:
Mass = Moles * Molar mass Mass = 2.5 moles * 58.44 g/mol = 146.1 g
b) The molar mass of HCl (Hydrochloric acid) is approximately 36.46 g/mol. The number of molecules in a given mass can be calculated using Avogadro's number (6.022 x 10^23 molecules/mol). Therefore, the number of molecules in 15 g of HCl is:
Moles = Mass / Molar mass Moles = 15 g / 36.46 g/mol = 0.411 moles
Number of molecules = Moles * Avogadro's number Number of molecules = 0.411 moles * 6.022 x 10^23 molecules/mol = 2.47 x 10^23 molecules
c) Aluminium oxide (Al2O3) has 2 Aluminium atoms and 3 Oxygen atoms, for a total of 5 atoms per formula unit. Therefore, the number of atoms in 6.6 moles of Aluminium oxide is:
Number of atoms = Moles * Avogadro's number * atoms per formula unit Number of atoms = 6.6 moles * 6.022 x 10^23 molecules/mol * 5 atoms/formula unit = 1.98 x 10^25 atoms
d) The molar mass of water (H2O) is approximately 18.02 g/mol, and there are 2 Hydrogen atoms per molecule of water. Therefore, the number of Hydrogen atoms in 7.0 g of water is:
Moles = Mass / Molar mass Moles = 7.0 g / 18.02 g/mol = 0.388 moles
Number of Hydrogen atoms = Moles * Avogadro's number * Hydrogen atoms per molecule Number of Hydrogen atoms = 0.388 moles * 6.022 x 10^23 molecules/mol * 2 Hydrogen atoms/molecule = 4.67 x 10^23 Hydrogen atoms
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