Question

How many hydrogen atoms are in 35.0 grams of hydrogen gas? How many hydrogen atoms are in 35.0 grams of hydrogen gas? 4.25 × 1025 2.12 × 1025 1.05 × 1025 2.09 × 1025 none of the above

Answer 1

Answer:

1.05 × 10²⁵ atoms H₂

General Formulas and Concepts:

Atomic Structure

• Reading a Periodic Table
• Moles

Stoichiometry

• Using Dimensional Analysis

Explanation:

Step 1: Define

[Given] 35.0 g H₂

[Solve] atoms H₂

Step 2: Identify Conversions

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

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

Molar Mass of H₂: 2(1.01) = 2.02 g/mol

Step 3: Convert

1. [DA] Set up:                                                                                                       $\displaystyle 35.0 \ g \ H_2(\frac{1 \ mol \ H_2}{2.02 \ g \ H_2})(\frac{6.022 \cdot 10^{23} \ atoms \ H_2}{1 \ mol \ H_2})$
2. Simplify [Cancel out units]:                                                                               $\displaystyle 1.04342 \cdot 10^{25} \ atoms \ H_2$

Step 4: Check

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

1.04342 × 10²⁵ atoms H₂ ≈ 1.04 × 10²⁵ atoms H₂

Topic: AP Chemistry

Unit: Atomic Structure