Relative Masses Of Atoms And Molecules
Overview
Atoms are far too small to weigh one at a time, so chemists compare their masses instead. By measuring every atom against one-twelfth of a carbon-12 atom, we get a simple scale of relative masses that lets us add up the mass of any molecule and predict how much product a reaction will make.
In this lesson you will learn what relative atomic mass and relative molecular mass mean, how to calculate the relative molecular mass of a compound, and how to use simple proportion to work out reacting masses. No mole calculations are needed here, just careful arithmetic and clear reasoning.
Objectives
- Describe relative atomic mass, A , as the r average mass of the isotopes of an element compared to 1/12th of the mass of an atom of 12C.
- Define relative molecular mass, M , as the sum r of the relative atomic masses. Relative formula mass, M , will be used for ionic compounds r.
- Calculate reacting masses in simple proportions. Calculations will not involve the mole concept.
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Lesson Evaluation
Congratulations on completing the lesson on Relative Masses Of Atoms And Molecules. 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.
- Relative atomic mass compares the average mass of an element's isotopes with: A. The mass of a hydrogen atom B. One-twelfth of the mass of a carbon-12 atom C. The mass of an oxygen atom D. One gram Answer: B
- What is the relative molecular mass of water, H2O? (Ar: H = 1, O = 16) A. 17 B. 18 C. 19 D. 34 Answer: B
- What is the relative molecular mass of carbon dioxide, CO2? (Ar: C = 12, O = 16) A. 28 B. 32 C. 44 D. 56 Answer: C
- What mass of carbon dioxide is formed when 12 g of carbon burns completely in oxygen? (C + O2 -> CO2) A. 12 g B. 22 g C. 32 g D. 44 g Answer: D
- The term used for the sum of relative atomic masses in an ionic compound is: A. Relative atomic mass B. Relative formula mass C. Molar volume D. Avogadro number Answer: B
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