Question

76.4 g of water H20 contain how many molecules?

Answer 1

2.55 × 10²⁴ molecules H₂O

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

• Reading a Periodic Table
• Moles
• Avogadro's Number - 6.022 × 10²³ atoms, molecules, formula units, etc.

Stoichiometry

• Using Dimensional Analysis

Step-by-step explanation:

Step 1: Define

[Given] 76.4 g H₂O

[Solve] molecules H₂O

Step 2: Identify Conversions

Avogadro's Number

[PT] Molar Mass of H - 1.01 g/mol

[PT] Molar Mass of O - 16.00 g/mol

Molar Mass of H₂O - 2(1.01) + 16.00 = 18.02 g/mol

Step 3: Convert

1. [DA] Set up:
   `\displaystyle 76.4 \ g \ H_2O((1 \ mol \ H_2O)/(18.02 \ g \ H_2O))((6.022 \cdot 10^(23) \ molecules \ H_2O)/(1 \ mol \ H_2O))`
2. [DA] Divide/Multiply [Cancel out units]:
   `\displaystyle 2.55317 \cdot 10^(24) \ molecules \ H_2O`

Step 4: Check

Follow sig fig rules and round. We are given 3 sig figs.

2.55317 × 10²⁴ molecules H₂O ≈ 2.55 × 10²⁴ molecules H₂O