Question

How many formula units make up 21.6 g of magnesium chloride (MgCl2)? Express the number of formula units numerically.

Answer 1

Answer:

1.37 × 10²³ formula units MgCl₂

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

[Given] 21.6 g MgCl₂

Step 2: Identify Conversions

Avogadro's Number

[PT] Molar Mass of Mg - 24.31 g/mol

[PT] Molar Mass of Cl - 35.45 g/mol

Molar Mass of MgCl₂ - 24.31 + 2(35.45) = 95.21 g/mol

Step 3: Convert

1. [DA] Set up:                                                                                                     $\displaystyle 21.6 \ g \ MgCl_2(\frac{1 \ mol \ MgCl_2}{95.21 \ g \ MgCl_2})(\frac{6.022 \cdot 10^{23} \ formula \ units \ MgCl_2}{1 \ mol \ MgCl_2})$
2. [DA] Multiply/Divide [Cancel out units]:                                                        $\displaystyle 1.36619 \cdot 10^{23} \ formula \ units \ MgCl_2$

Step 4: Check

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

1.36619 × 10²³ formula units MgCl₂ ≈ 1.37 × 10²³ formula units MgCl₂