The Mole Concept
Overview
A balance in a school laboratory can tell you that a strip of magnesium weighs 0.1 g. What it cannot tell you, and what a chemist actually wants to know, is that the strip holds roughly two and a half thousand billion billion atoms. Chemical equations are written in particles: two of these react with one of those. Balances are built to read grams. Somewhere between those two facts there has to be a translator, and the mole is it.
This lesson introduces the one unit that lets a laboratory balance behave as a counting machine. You will meet the number that every mole contains, find out why that particular number and no other was chosen, and learn to move in both directions between a mass in grams and an amount in moles. By the end you will be able to look at 9.0 g of water and 22 g of carbon dioxide and say, without hesitation, that the two samples contain exactly the same number of molecules, and you will know why a real examination question asks a student to weigh out 0.050 mol of a metal rather than 3 g of it.
Objectives
- The relative formula mass of a substance, in grams, is known as one mole of that substance. Students should be able to use the relative formula mass of a substance to calculate the number of moles in a given mass of that substance and vice versa.
- One mole contains 6.02 × 1023 atoms or molecules. This number is known as Avogadro’s constant.
Mind map
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Lesson Note
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Lesson Evaluation
Congratulations on completing the lesson on The Mole Concept. Now that youve explored the key concepts and ideas, its time to put your knowledge to the test. This section offers a variety of practice questions designed to reinforce your understanding and help you gauge your grasp of the material.
You will encounter a mix of question types, including multiple-choice questions, short answer questions, and essay questions. Each question is thoughtfully crafted to assess different aspects of your knowledge and critical thinking skills.
Use this evaluation section as an opportunity to reinforce your understanding of the topic and to identify any areas where you may need additional study. Don't be discouraged by any challenges you encounter; instead, view them as opportunities for growth and improvement.
- One mole of any substance contains the same number of particles. What is this number? A. 6.02 x 10^22 B. 6.02 x 10^23 C. 6.02 x 10^24 D. 1.00 x 10^23 Answer: B
- The relative formula mass of calcium carbonate, CaCO3, is 100. What is the mass of 0.20 moles of calcium carbonate? A. 5 g B. 20 g C. 50 g D. 500 g Answer: B
- A sample of sodium has a mass of 4.6 g. The relative atomic mass of sodium is 23. How many moles of sodium atoms are in the sample? A. 0.20 mol B. 0.50 mol C. 2.0 mol D. 5.0 mol Answer: A
- 0.25 moles of a compound has a mass of 10 g. What is the relative formula mass of the compound? A. 2.5 B. 10 C. 40 D. 250 Answer: C
- A student needs 0.050 mol of zinc. The relative atomic mass of zinc is 65. What mass of zinc should be weighed out? A. 1.3 g B. 3.25 g C. 13 g D. 1300 g Answer: B
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