# Chemistry Question

Slide notes
Welcome to the Unit I Knowledge Check
These Knowledge Checks are designed to provide practice on math-heavy
portions of your quizzes and homework assignments.
You will learn from any correct answers, or any mistakes you make, by being
given immediate feedback.
You can, and should, go back through these Knowledge Checks as many
times as necessary to fully master this information (It also helps you prepare
Page 1 of 11
Unit I Homework
Slide 2 – Mass & Volume
Slide notes
• Given the mass and volume of several objects.
2) Divide its mass (g) by its volume (mL).
3) The object with the largest number, after your calculation, has the highest
density.
 You are asked to find the object with the highest density.The key point is to:
1) convert each object’s mass into grams (g) and its volumes into milliliters
(mL).
1. Which of the items below would be considered the densest?
Page 2 of 11
Slide 3 – Density
Slide notes
• Density in SI derived units are in (Kg/m3) but typically expressed in smaller
units of (g/mL)
 You will be expressing your Density for each object in (g/mL)
• So for problem #1 you will use:
1. Which of the items below would be considered the densest?
Density = Mass (g)/ Volume (mL)
Slide 4 – Unit Equivalents
Page 3 of 11
Slide notes
Mass (g)
Volume (ml)
Just as a quick reminder, you will need to memorize your prefixes and their
meanings.
There’s a table for this in your textbook. I’d suggest creating flashcards or
maybe creating a quiz on quizzlet for example.
1. What is the name of the unit that equals a 10-9 gram?
2. d. Nanogram
1. What is the name of the unit that equals a 1012 bytes?
a. Terabyte
Page 4 of 11
Slide 5 – Unit Conversion
Slide notes
Here’s an example of how to answer one of these questions.
But remember, we need to convert all objects.
A bowling ball with a volume of 3.5 L and a mass of 13.5 kg.
Density =
Mass
Volume
Slide 6 – Unit Conversion
Page 5 of 11
Slide notes
Let’s convert Kg into g by multiplying a ratio where the denominator has the
unit we want to get rid of.
Here that unit is Kg.
Notice that I put a 1 in front of the unit with a prefix.
A bowling ball with a volume of 3.5 L and a mass of 13.5 kg.
Density =
Slide 7 – Unit Prefixes
Page 6 of 11
Slide notes
We want units of grams “g” in the numerator but we have to be sure the
math makes sense.
Kilo means 103 so that’s what we put in the numerator. Now we can reward
ourselves by crossing out Kg.
Now we must put the meaning of the prefix Kilo in front of the base unit g.
A bowling ball with a volume of 3.5 L and a mass of 13.5 kg.
Slide 8 – Unit Conversion
Page 7 of 11
Slide notes
We want units of “mL” in the denominator so now we’ll have to multiply by
another ratio to make this happen.
Liters must cancel out so that’s what we put into the numerator. We also put
mL in the denominator because those are the units we want.
A bowling ball with a volume of 3.5 L and a mass of 13.5 kg.
Liters
Slide 9 – Complete the Equation
Page 8 of 11
Slide notes
At this point, remember, we give the unit with the prefix the number 1. The
base unit Liters has the meaning of milli in front of it, which is 10-3.
We cross out Liters and now we have the units we want.
A bowling ball with a volume of 3.5 L and a mass of 13.5 kg.
Slide 10 – Abundance
Page 9 of 11
Slide notes
The key point is, for each isotope, to multiply its mass times its abundance.
Once you have done this for each isotope simply add each result.
Slide 11 – Complete the problem
Page 10 of 11
Slide notes
Here’s an example of how to answer one of these questions
Find the Average Atomic Mass for isotopes 12C with 12 amu, occurring at
98.93%, and 13C with 13.00335 amu occurring at 1.07%.
AMU = Atomic Mass Unit
12C isotope = (12 amu X 0.9893)
+
13C isotope = (13.00335 amu X 0.0107)
= 12.01 amu
Page 11 of 11

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