Homework 2

CHEM& 140 – Checkpoint 13 – Show It HW Name ________________________________ Section ___

The notation at the beginning of each problem refers to the location of the problem in the textbook (6th edition of Introductory Chemistry by Tro). Most odd-numbered problems have answers in the back of the book.

1. (CH6 #2) How can you efficiently determine the number of atoms in a sample of an element? Why is counting them not an option?

2. (CH6 #3 & #4) How many atoms are in 1 mole of atoms? How many molecules are in 1 mole of molecules?

3. Let’s say you have 1 mole of carbon and 1 mole of carbon dioxide.

· Do these samples have the same mass? Determine the mass of each sample.

· Do these samples have the same number of total atoms? Determine the total number of atoms present in each sample.

· What can you say is the same about these two samples since they both are 1 mole samples?

4. What is the difference between a formula mass (or a molecular mass) versus a molar mass? What are the units for each?

Do pages 77-82 of the CHEM& 140 Workbook (2020 version).

5. (3 pts out of 10pts) Insert photos of your work for pages 80-81 of the CHEM& 140 Workbook (2020 version). You MUST show your calculation set up including units in all steps and show how the units cancel out to get to the final answer. You may use dimensional analysis or proportions.

6. (2 pts out of 10pts) Insert photo of your answers for page 82 of the CHEM& 140 Workbook (2020 version). You do not have to show your work for this page. For the last two rows, use the units of molar mass to help you figure out how to use the other values to get molar mass!

7. Taking into account the problem solving you used on the Workbook problems, what additional steps would be needed for the following two problems? Include a problem-solving plan for each, including the quantities that you’ll be converting to/from/between and the conversion factors you will use for each step.

Example: Convert 3 days into seconds. Plan: days h min s

1 day = 24 h 1 h = 60 min 1 min = 60 s

· (CH6 #42) How many copper atoms are in a pure copper statue with a mass of 133 kg?

· (CH6 #56) A salt crystal has a mass of 0.12 mg. How many NaCl formula units does it contain?