Mole-particles calculations

Example: Calculating the number of moles in the given number of atoms

Titanium is corrosion resistant metal that is used in rockets, aircrafts and jet engines. Calculate the number of moles of this metal in a sample containing 3.011 x 10²³ Ti-atoms.

Tactics:

To calculate number of moles from a given number of particles (atoms), write an equation by placing number of moles (unknown quantity ) on right hand side and number of atoms (known quantity) on left hand side of the equation and follow these steps.

Step 1:

First write a known relation between these particles (known quantity) and mole (unknown quantity) with mole on right hand side of the equation.

6.022 × 10²³ atoms = 1 mole.

Step 2:

Next, find number of moles (unknown quantity) for '1' atom of known quantity (by dividing with i.e., 6.022 × 10²³) . If already there is 1 on the left side of equation, then no need of step 2.

Step 3

Then, multiply the equation with given quantity and value on right hand side of equation will be the required quantity.

Solution:

Step 1:

6.022 × 10²³ atoms of Ti = 1 mole of Ti

Step 2:

1 Ti atom = 1/6.022 × 10²³ moles of Ti

Step 3:

3.011 × 10²³ Ti atoms = 3.011 x 10²³ × 1/6.022 x 10²³

= 0.5 moles of Ti

Example: Formaldehyde is used to preserve dead animals. Its molecular formula is CH₂O. Calculate the number of moles that would contain 3.011 × 10²² molecules of this compound.

Solution:

6.022 × 10²³ molecules of formaldehyde = 1 mole of formaldehyde

1 molecule of formaldehyde

= 1/6.022 × 10²³ moles of formaldehyde

= 3.011 × 10²² molecule of formaldehyde

= 3.011 x 10²² × 1 /6.022 × 10²³

= 0.05 moles of formaldehyde

Self-Assessment

Aspirin is a compound that contains carbon, hydrogen and oxygen. It is used as a painkiller. An aspirin tablet contains 1.25 × 10³⁰ molecules. How many moles of this compound are present in the tablet?

Solution

6.022 × 10²³ molecules of aspirin = 1 mole of aspirin

1 molecule of aspirin = 1/6.022 x 10²³ moles of aspirin

1.25 × 10³⁰molecule of formaldehyde = 1.25 × 10³⁰ × 1 /6.022 × 10²³

= 2.0 × 10⁸ moles of aspirin

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