High School

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Determine the number of atoms in each sample.

a.) 98.3 g mercury, Hg
c.) 10.7 g lithium, Li

Determine the number of moles in each sample.

a.) 6.84 g sucrose, C\(_{12}\)H\(_{22}\)O\(_{11}\)
c.) 68.0 g ammonia, NH\(_3\)

Determine the mass of the following molar quantity.

a.) 3.52 mol Si
c.) 0.550 mol F\(_2\)

Answer :

So there are three formulas that you must be aware of hen attempting these questions (by technicality, only two because the third is a transposition of the second).

These formulas are :

mole x L = # of atoms (where L = Avogadro's Constant)

mass / Mr = mole (where Mr = Molar Mass)

Mole x Mr = mass

So no we can easily ace these questions

1) a. 98.3 g of Hg

mass of Hg = 98.3g

Mr " " = 201 g / mol

mole = [tex] \frac{98.3 g}{201 g / mol} [/tex]

= 0.489 mol

∴ # of atoms = 0.489 mol * (6.03 * 10²³)

= 2.95 * 10²³ atoms

c. 10.7g of Li

mass of Li = 10.7 g

Mr " " = 7 g / mol

thus mole = [tex] \frac{10.7g}{7 g / mol} [/tex]

= 1.529 mol

# of atoms = 1.529 mol * (6.03 * 10²³)

= 9.22 * 10²³

2) a. 6.84 g of C₁₂H₂₂O₁₁

mass of sucrose = 6.84 g

Mr " " = ∑ (Mr of each element * amount of each element's atom)

= ∑ [(12 * 12)+(1 * 12)+(16 * 11)] g / mol

= 342 g / mol

∴ mole of sucrose = [tex] \frac{6.84 g}{342 g / mol} [/tex]

= 0.02 mol

c) 68.0g of NH₃

mass of NH₃ = 68.0 g

Mr " " = [(14 * 1) + ( 1 * 3)] g / mol

∴ mole of NH₃ = [tex] \frac{68.0 g }{17 g / mol} [/tex]

= 4 mol


3) a. 3.52 mol of Si

mole of Si = 3.52 mol

Mr " " = 28 g / mol

Mass = 3.52 mol * 28 g / mol

= 98.56 g

c. 0.550 mol of F₂

mol of F₂ = 0.55 mol

Mr " " = (19 * 2 ) g / mol

Mass = 0.55 mol * 38 g / mol

= 20.9 g


Hope I as clear in my answers and that they helped

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