Question

A sample of gold (Au) has a mass of 35.12 g.

a.
Calculate the number of moles of gold (Au) in the sample. Show your work.


b.
Calculate the number of atoms of gold (Au) in the sample. Show your work

Answer 1

a. 0.18 mol

b. 1.084 x 10²³ atoms

Step-by-step explanation:

Data Given:

mass of gold (Au) = 35.12 g

a. number of moles of gold (Au) = ?

b. number of atoms of gold (Au) =?

Solution:

Part a:

To find number of moles following formula will be used

no. of moles = mass in grams / molar mass . . . . . . (1)

molar mass of gold (Au) = 197 g/mol

put values in equation 1

no. of moles = 35.12 g / 197 g/mol

no. of moles = 0.18 mol

so. number of moles of Au = 0.18 mol

_________________

Part b:

To find number of atoms following formula will be used

no. of moles = no. of atoms / Avogadro's number

Rearrange the above equation

no. of atoms = no. of moles x Avogadro's number . . . . . . . (2)

Avogadro's number = 6.022 x 10²³ atoms /mol

put values in equation 1

no. of atoms = 0.18 mol x 6.022 x 10²³

no. of atoms = 1.084 x 10²³

so.

number of atoms of Au = 1.084 x 10²³ atoms

Answer 2

Step-by-step explanation:

Given data:

Mass of gold = 35.12 g

Number of moles of gold = ?

Number of atoms of gold = ?

Solution:

A) Number of moles:

Formula:

Number of moles = mass/ molar mass

Molar mass of gold = 197 g/mol

Number of moles = 35.12 g/ 197 g/mol

Number of moles = 0.18 mol

B) Number of atoms:

The given problem will solve by using Avogadro number.

It is the number of atoms , ions and molecules in one gram atom of element, one gram molecules of compound and one gram ions of a substance.

The number 6.022 × 10²³ is called Avogadro number .

One mole = 6.022 × 10²³ atoms

0.18 mol × 6.022 × 10²³ atoms / 1mol

1.084 × 10²³ atoms of gold