Question

What is the mass of 1.20 x 10^25 atoms of He

Answer 1

Answer:

79.7 g He

General Formulas and Concepts:

Chemistry - Atomic Structure

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

Explanation:

Step 1: Define

1.20 × 10²⁵ atoms He

Step 2: Identify Conversions

Avogadro's Number

Molar Mass of He - 4.00 g/mol

Step 3: Convert

$1.20 \cdot 10^{25} \ atoms \ He(\frac{1 \ mol \ He}{6.022 \cdot 10^{23} \ atoms \ He} )(\frac{4.00 \ g \ He}{1 \ mol \ He} )$ = 79.7077 g He

Step 4: Check

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

79.7077 g He ≈ 79.7 g He