Question

Calculate the number of Li atoms in 7.8 mol of Li.

Express your answer using two significant figures.

Answer 1

4.7 × 10²⁴ atoms Li

General Formulas and Concepts:

Math

Pre-Algebra

Order of Operations: BPEMDAS

1. Brackets
2. Parenthesis
3. Exponents
4. Multiplication
5. Division
6. Addition
7. Subtraction

• Left to Right

Chemistry

Atomic Structure

• Avogadro's Number - 6.022 × 10²³ atoms, molecules, formula units, etc.

Stoichiometry

• Using Dimensional Analysis

Step-by-step explanation:

Step 1: Define

7.8 mol Li

Step 2: Identify Conversions

Avogadro's Number

Step 3: Convert

1. Set up:
   `\displaystyle 7.8 \ mol \ Li((6.022 \cdot 10^(23) \ atoms \ Li)/(1 \ mol \ Li))`
2. Multiply/Divide:
   `\displaystyle 4.69716 \cdot 10^(24) \ atoms \ Li`

Step 4: Check

We are told to round to 2 sig figs. Follow sig fig rules and round.

4.69716 × 10²⁴ atoms Li ≈ 4.7 × 10²⁴ atoms Li