Question

How many moles of Ca are in 1.25x1023 atoms?

We used two conversion factors in this unit, they are provided below. It is your responsibility to know which conversion factor to use!

Avogadro’s number: 6.02x1023 atoms = 1 mole

Molar mass of calcium: 40.078 g Ca = 1 mol Ca


A. 3.12x10^21 mol


B. 0.21 mol


C. 3.12 mol


D. 0.21x10^21 mol

Answer 1

B. 0.21 mol

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

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

Step-by-step explanation:

Step 1: Define

1.25 × 10²³ atoms Ca

Step 2: Identify Conversions

Avogadro's Number

Step 3: Convert

1. Set up:
   `\displaystyle 1.25 \cdot 10^(23) \ atoms \ Ca((1 \ mol \ Ca)/(6.022 \cdot 10^(23) \ atoms \ Ca))`
2. Multiply:
   `\displaystyle 0.207572 \ mol \ Ca`

Step 4: Check

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

0.207572 mol Ca ≈ 0.208 mol Ca