All rights reserved. Zach Jones 1 CP Chemistry Unit 1 – Tools of a Chemist Learning Objectives 1.1 Basic Measurement and Density 1.2 Dimensional Analysis 1.3 Error in Measurement Progress Tracker Test Date: Webassign Due Score Packet Progress Checks Test Readiness Checks: □ My webassign scores indicate I am ready for the test. □ I went to ASP for Webassign help when needed. □ I have completed the unit review AND checked my answers. □ I am aware that I cannot retake the test unless my webaassign and packet progress checks are all 1.1 Basic Measurement and Density Convert a standard number to scientific notation and back. (6.20x10 -2 = 0.0620) Demonstrate an understanding of the relative size of numbers presented in scientific notation. Make accurate measurements of length, volume, and mass in the laboratory and consistently report appropriate units. Measure and calculate the density of solids and liquids. = Be able to use the volume displacement technique. Solve for volume or mass algebraically given density data. Conceptually relate density to particulate representations. Given a graph of the density of an object, be able to predict the graph of another object given density information. Use graphical representations to find the density of an object. Understand that density is an intrinsic property of a substance and demonstrate an understanding of the independence on amount of the substance. Relate density to sinking and floating. Design an experiment to measure the density of a substance and report an appropriate procedure and data table.
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All rights reserved. Zach Jones 1
CP Chemistry
Unit 1 – Tools of a Chemist
Learning Objectives 1.1 Basic Measurement and Density
1.2 Dimensional Analysis
1.3 Error in Measurement
Progress Tracker
Test Date:
Webassign Due Score
Packet Progress Checks
Test Readiness Checks: □ My webassign scores
indicate I am ready for
the test.
□ I went to ASP for
Webassign help when
needed.
□ I have completed the unit
review AND checked my
answers.
□ I am aware that I cannot
retake the test unless my
webaassign and packet
progress checks are all
above 80%.
1.1 Basic Measurement and Density
Convert a standard number to scientific notation and back. (6.20x10-2 = 0.0620)
Demonstrate an understanding of the relative size of numbers presented in scientific notation.
Make accurate measurements of length, volume, and mass in the laboratory and consistently report appropriate units.
Measure and calculate the density of solids and liquids.
𝐷 = 𝑀
𝑉
Be able to use the volume displacement technique.
Solve for volume or mass algebraically given density data.
Conceptually relate density to particulate representations.
Given a graph of the density of an object, be able to predict the graph of another object given density information.
Use graphical representations to find the density of an object.
Understand that density is an intrinsic property of a substance and demonstrate an understanding of the independence on amount of the substance.
Relate density to sinking and floating.
Design an experiment to measure the density of a substance and report an appropriate procedure and data table.
Need help with Chem? Go to www.mrjoneslhsscience.weebly.com 2
Key Skill: Identifying the significant figures in a measurement.
Information: All measurement equipment has limits on how accurately the measurement can be recorded. We
have seen that the number of digits that the measurement can have is dependent on the number of lines marked on
the side of the glassware or other device. A really precise piece of glassware can produce lots of digits (which we
will call significant figures from now on.)
One piece of metal is weighed on two different balances. Here are the results:
Balance A: 2.3 g This is a cheap (inexpensive) and low precision balance that produces 2 digits.
Balance B: 2.38 g This is a better (and more expensive) balance that produces 3 digits.
Some digits in a measurement, however, have are never important (or significant) because they are simply place
holders. In the measurement 0.37 g, the bolded zero was not really measured, it simply emphasized the location of
the decimal. Here are 3 important rules for determining if a digit is significant or not:
1. Zeros at the beginning of a number are never significant (important). 2. Zeros at the end of a number are not significant unless… (you’ll find out later) 3. Zeros that are between two nonzero numbers are always significant.
Therefore, the number 47,200 has three significant figures: only three of the digits are important—the four, the
seven, and the two. The number 16,150 has four significant figures because the zero at the end is not considered
significant. All of the digits in the number 20,007 are significant because the zeros are in between two nonzero
numbers (Rule #3).
Critical Thinking Questions
1. Verify that each of the following numbers contains four significant figures. Circle the digits that are significant. a) 0.00004182 b) 494,100,000 c) 32,010,000,000 d) 0.00003002
2. How many significant figures are in each of the following numbers? _____ a) 0.000015045 _____ b) 4,600,000 _____ c) 2406
In numerical problems, it is often necessary to round numbers to the appropriate number of significant figures.
Consider the following examples in which each number is rounded so that each of them contains 4 significant
figures. Study each example and make sure you understand why they were rounded as they were:
42,008,000 42,010,000
12,562,425,217 12,560,000,000
0.00017837901 0.0001784
120 120.0
Critical Thinking Questions
5. Round the following numbers so that they contain 3 significant figures.
a) 173,792 b) 0.0025021 c) 0.0003192 d) 30
_________ ___________ __________ __________
6. Round the following numbers so that they contain 4 significant figures.
a) 249,441 b) 0.00250122 c) 12,049,002 d) 0.00200210
__________ ___________ ____________ _____________
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CP Chemistry
Key Skill: Reporting the answer of a calculation to the correct number of
significant figures. Case #1: Multiplying and Dividing
When measuring the density of a substance, a student records the mass to be 38.41 g from the balance, and they
recorded the volume to be 48 mL from your beaker. Which of these two values is a better measurement? Explain:
When you calculate the density by dividing 38.40 by 48 you get 0.800208333333 g/mL.… How many of those digits
should we write down? A good rule of thumb is that the final answer can’t have more significant figures than the
measurement with the least amount of accuracy. Think of it this way: If person is playing a guitar and singing, and
they are an amazing guitarist, but sing horribly out of tune, the song will end up sounding horrible anyway. This is
the same idea with measurements. Here’s how to do the math:
1) Count the number of significant figures in each number that you are using in the calculation. 2) Round your answer so that it has the same number of significant figures as the number with the
1. Two of the following six numbers are written incorrectly. Circle the two that are incorrect.
a) 3.57 x 10-8 b) 4.23 x 10-2 c) 75.3 x 102 d) 2.92 x 109 e) 0.000354 x 104 f) 9.1 x 104
2. What do you think is wrong about the two numbers you circled? Explain.
3. For each of these, write the number in scientific notation:
a. 0.00451 _____________ (Did you put the decimal to the right of the 4?) b. 80,340 _____________ (Did you put the decimal to the right of the 8?) c. 0.00683 _____________ d. 602,000,000 ____________
4. For each of these, convert the number to standard notation (a normal number):
a. 9.1 x 104 ____________ b. 2.92 x 10-2 ____________ c. 6.50 x 10-5 ____________ d. 1.1 x 106 _____________
5. In each of these pairs, circle the larger number. It may help to convert them from scientific notation to
standard numbers to compare. (One of them is a trick question!)
a. 0.06 or 4.1 x 10-3
b. 3.67 x 102 or 3.67 x 101
c. 8 x 10-3 or 7 x 10-2
d. 21.3 x 10-5 or 2.13 x 10-4
e. 5.4 x 104 or 54 x 104
________________________________________________ Check with Instructor
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CP Chemistry
Reflecting on Significant Figures
1. What is a significant figure? Why aren’t ALL numbers significant? _______________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________
2. Why do we have to adjust the answer to a calculation to the correct number of significant figures? What do we mean by one of the numbers being “weaker” than the other? _________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________
3. Contrast how you determine the number of significant figures in an answer when multiplying/dividing with how you find them when adding in subtracting. How is the process different .______________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________
Key Skill: Use a unit cancelling technique to convert one type of unit into
another.
To Do:
Go to the following website: http://joneslhs.weebly.com
Click on the Learn button on the left. Read the tutorial first. When you think that you understand the idea, go back to the Main Menu and click on One Step Conversions.
One Step Conversions
For problems 1, 2, and 3 write down what the completed problem looks like after you have done it on the computer. Cancel the units that cancel. Circle the unit that doesn’t cancel. Write down the answer to the problem.
1.
=
2.
=
3.
=
For problems 4-9, you can just write down the answer once you have solved it.
4. Calculated Answer:
5. Calculated Answer:
6. Calculated Answer:
7. Calculated Answer:
8. Calculated Answer:
9. Calculated Answer:
For problem 10, solve it on paper here without using the computer. Then type in the calculated answer to see if you are
correct. SHOW YOUR WORK FOR PROBLEM 10 here:
________________________________________________ Check with Instructor before moving on.
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CP Chemistry
Multi-Step Conversions
For problems 1, 2, and 3 write down what the completed problem looks like. Cancel the units that cancel. Circle the unit that is the one left at the end. Write down the answer to the problem.
1.
=
2.
=
3.
=
For problems 4-10, you can just write down the answer once you have solved it.
4. Calculated Answer:
5. Calculated Answer:
6. Calculated Answer:
7. Calculated Answer:
8. Calculated Answer:
9. Calculated Answer:
For problem 10, solve it on paper here without using the computer. Then type in the calculated answer to see if
you are correct. SHOW YOUR WORK FOR PROBLEM 10 here:
________________________________________________ Check with Instructor before moving on.
Read the directions on the first problem to see how to get started. Work through the challenging problems recording your answer for each one. Don’t forget units!
1. Calculated Answer:
2. Calculated Answer:
3. Calculated Answer:
4. Calculated Answer:
5. Calculated Answer:
6. For problem 6, solve it on paper here. Then type in the calculated answer to see if you are correct.
Cubed and Squared Conversions
Read the directions on the first problem to see how to get started. Work through the challenging problems recording your answer for each one. Don’t forget units!
1. Calculated Answer:
2. Calculated Answer:
3. Calculated Answer:
4. For problem 4, solve it on paper here. Then type in the calculated answer to see if you are correct.
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CP Chemistry
Conversion Factors:
1 horse = 3 cows
10 cows = 1 bird
3 birds = 5 lemons
9 lemons = 1 orange
2 oranges = 5 fords
1 ford = 6 trucks
Nonsense Units Practice
Using the conversion table, solve the problems. No credit given if “dimensional