Question

Determine the number of atoms in each sample.

a.) 98.3 g mercury, Hk

c.) 10.7 g lithium, Li

Determine the number of moles in each sample.

a.) 6.84g sucrose C12H22)11

c.) 68.0g ammonia, NH3

Determine the mass of the following molar quantity.

a.) 3.52 mol Si

c.) 0.550 mol F2




Chemistry, year1, honors. Can *someone* PLEASE help me?

Answer 1

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 =
`(98.3 g)/(201 g / mol)`

= 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 =
`(10.7g)/(7 g / mol)`

= 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 =
`(6.84 g)/(342 g / mol)`

= 0.02 mol

c) 68.0g of NH₃

mass of NH₃ = 68.0 g

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

∴ mole of NH₃ =
`(68.0 g )/(17 g / mol)`

= 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