Question

1. How many moles are present in 9.25x10^34 molecules of H2O?

2. How many moles are present in 4.51x10^15 atoms of Aluminum (AI)?

3.How many moles are present in 3.78x10^20 atoms of Lithium (Li)?

Answer 1

What is Stoichiometry?

Stoichiometry is the relationship between two substances through use of ratios.

To answer these questions, you must use the ratio:

1 mol of a substance

6.022 × 10²³ molecules

Let's try the first question:

9.25 × 10³⁴ molecules H₂O × 1 mol H₂O

6.022 × 10²³ molecules

The molecules will cancel out, leaving you with

9.25 × 10³⁴ mol

6.022 × 10²³ mol

Use your calculator to solve: 1.536 × 10¹¹ mol H₂O

Now, follow this same format to solve the rest of the questions:

2) 4.51 × 10¹⁵ molecules Al × 1 mol Al

6.022 × 10²³ molecules

= 4.51 × 10¹⁵ mol Al

6.022 × 10²³ mol Al

= 7.489 × 10⁻⁹ mol Al

3) 3.78 × 10²⁰ molecules Li × 1 mol Li

6.022 × 10²³ molecules

0.0006276 mol Li

_________________________________________________________

1. 1.536 × 10¹¹ mol H₂O
2. 7.489 × 10⁻⁹ mol Al
3. 0.0006276 mol Li