Question

Given 4.20 x 1022 molecules of He gas, what mass of He do you have?

Answer 1

Answer:

0.279 g He

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

Stoichiometry

• Using Dimensional Analysis

Explanation:

Step 1: Define

4.20 × 10²² molecules He

Step 2: Identify Conversions

Avogadro's Number

[PT] Molar Mass of He - 4.00 g/mol

Step 3: Convert

1. Set up:                              $\displaystyle 4.20 \cdot 10^{22} \ molecules \ He(\frac{1 \ mol \ He}{6.022 \cdot 10^{23} \ molecules \ He})(\frac{4.00 \ g \ He}{1 \ mol \ He})$
2. Multiply/Divide:                                                                                               $\displaystyle 0.278997 \ g \ He$

Step 4: Check

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

0.278997 g He ≈ 0.279 g He