1. YOYO
Review Questions – 10 Multiple choice questions in the Unit 2 HW Packet (Pages 5-7)

2. Question 1
Matter that is composed of two or more different elements chemically combined in a fixed proportion is classified as
a compound
an element
a mixture
a solution

3. Which statement is an identifying characteristic of a mixture?
Question 2
Which statement is an identifying characteristic of a mixture?
a mixture can consist of a single element
a mixture can be separated by physical means
a mixture must have a definite composition by weight
a mixture must be homogeneous

4. Which substance cannot be broken down by a chemical reaction?
Question 3
Which substance cannot be broken down by a chemical reaction?
Ammonia
Argon
Methane
Water

5. Question 4
Two substances A and Z are to be identified. Substance A cannot be broken down by a chemical change. Substance Z can be broken down by a chemical change. What can be concluded about these substances?
Both substances are elements
Both substances are compounds
Substance A is an element and substance Z is compound
Substance A is a compound and substance Z is an element.

6. Question 5
A sample is prepared by completely dissolving 10.0 grams of NaCl in 1.0 liter of H2O. Which classification best describes this sample?
homogeneous compound
homogeneous mixture
heterogeneous compound
heterogeneous mixture

7. Which sample of matter is classified as a solution?
Question 6
Which sample of matter is classified as a solution?
H2O (s)
H2O (l)
CO2 (g)
CO2 (aq)

8. Which set of procedures and observations indicates a chemical change?
Question 7
Which set of procedures and observations indicates a chemical change?
Ethanol is added to an empty beaker and the ethanol eventually disappears.
A solid is gently heated in a crucible and the solid slowly turns to a liquid.
Large crystals are crushed with a mortar and pestle and become powder.
A cool, shiny metal is added to water in a beaker and rapid bubbling occurs.

9. Question 8
Which statement best describes the shape and volume of an aluminum cylinder at STP?
It has a definite shape and a definite volume
It has a definite shape and no definite volume
It has no definite shape and a definite volume
It has no definite shape and no definite volume

10. An aqueous solution of sodium chloride is classified as a
Question 9
An aqueous solution of sodium chloride is classified as a
homogeneous compound
homogeneous mixture
heterogeneous compound
heterogeneous mixture

11. Question 10
Given the particle diagram representing four molecules of a substance. Which particle diagram best represents this same substance after a physical change has taken place? Explain your answer in the empty space below. A. B. C. D.

12. Aim: Where did the mass on the periodic table come from
Aim: Where did the mass on the periodic table come from? (What is average atomic mass?)
Scanlon

13. Average Atomic Mass
Most elements have one or more naturally occurring isotopes
Isotope: has the same atomic number (# of protons), making it the same element, but has a different mass (# protons + # neutrons)
Basically, an isotope is a different version of a particular element with a different mass

14. Not All Masses are the Same
Yes there are these naturally occurring isotopes, BUT they do not all exist in the same percentages.
Isotope
Natural Abundance on Earth (%)
Atomic Mass (amu)
24Mg
78.99
25Mg
10.00
26Mg
11.01

15. So the number on the periodic table…where did that come from?
Math!
Because each isotope occurs in different proportions, we CANNOT just calculate a basic average.
Looking at our magnesium example
(78.99)( amu) + (10.00)( amu) + (11.01)( amu)
100 =
The Periodic table says…24.305