Download Unit 2.2 Test Review Key

Name: ___Teacher key____ Class Period: _______ Due Date: ______
Unit 2 – What are we made of?
Unit 2.2 Test Review
TEKS covered:
8.5D recognize that chemical formulas are used to identify substances and determine the
number of atoms of each element in chemical formulas containing substances
8.5F recognize whether a chemical equation containing coefficients is balanced or not and how
that relates to the law of conservation of mass
8.5E investigate how evidence of chemical reactions indicate that new substances with different
properties are formed
7.6A identify that organic compounds contain carbon, hydrogen, oxygen, phosphorus, nitrogen
or sulfur
7.6B distinguish between physical and chemical changes in matter
Answer the following questions:
1. Above is the chemical equation for photosynthesis.
a. Circle the coefficients.
b. Put a square around the subscripts.
c. How many elements are involved in the equation for
photosynthesis? 3
d. What are the elements involved in the equation for photosynthesis?
Carbon, Hydrogen, Oxygen
e. What are the compounds involved in the equation for
photosynthesis? C6H12O6, CO2, H2O
f. How many atoms of O are there in 6H2O? 6
g. What are the reactants in the equation for photosynthesis? CO2,
H2O
h. What are the products in the equation for photosynthesis? C6H12O6,
O2
2. What does the Law of Conservation of Mass state?
Mass is neither created nor destroyed during a chemical reaction
3.
How does the Law of Conservation of Mass impact the balancing of chemical
equations?
The Law of Conservation of Mass means that there are the same number and type
of atoms on the reactant side as there are on the product side, creating a balanced
equation.
4.
Explain what is happening with the mass and matter in a chemical equation.
Matter is conserved
or destroyed)
Mass is conserved
or destroyed)
type of atoms does not change (Nothing is created
amount of atoms cannot change (Nothing is created
5. Write if each equation demonstrates or does not demonstrate the Conservation of
Mass. Then explain why is does or does not demonstrate it.
Reaction
1
SnO2 + H2 → Sn + 2H2O
2
NH3 + HCl
3
2Rb + P
4
2C + 2SO2
NH4Cl
Rb3P
CS2 +
Demonstrates
or Does not
Demonstrate
Does not
demonstrate
Demonstrates
Does not
demonstrate
Does not
Why?
There are more hydrogen atoms in
the product than the reactant, so
mass is unbalanced
All types and amounts of atoms are
the same in the reactants and
products (mass and matter are
balanced)
There are more Rb atoms in the
products than the reactants, so
mass is unbalanced
There is a new element(or type of
2HO2
demonstrate
atom) on the product side, so
matter is unbalanced
6. In this chemical formula, 7H2OSP3
a. Which element has the greatest number of atoms? ____P___
b. What is the number of elements it has? __4_
7. List each element, and how many of each in the substance 7H2OSP3 ____
hydrogen – 14; O – oxygen – 7; S – Sulfur – 7, P - Phosphorus_21__
H-
8. Complete the chart below. In the “Evidence: How do you know” column, explain
how you know that the equation is a balanced or not balanced one.
Equation
2NaOH + H2CO3
H2O
Na2CO3 +
N2 + H2 → NH3
4FeS2 + 11O2
Balanced or Not
Balanced
Not Balanced
Not Balanced
2Fe2O3 + 8SO2
3Fe + 4H2O → Fe3O4 + 4H2
Balanced
Balanced
Evidence:
How do you know?
There are 4 H atoms in the
reactant and only 2 in the
product and there are more O
atoms in the reactant than in
the product
There are more N atoms in
the reactant than the product
and there are more hydrogen
atoms in the product than the
reactant
All types and amounts of
atoms are the same in the
reactants and products
All types and amounts of
atoms are the same in the
reactants and products
O
H
Pa
O
O
O
H
H
Write the chemical formula for the substance above. ____ H3PO4
9. Draw a model of H2O2 and 2OH in the table below.
Model
H
H
O
O
Atom Count
H=2
O= 2
H=2
H
O
H
O
O= 2
Are they, H2O2 and 2OH, the same substance? __No___
Explain your answer: No they are not the same substance even though they
have the same amount and type of atoms. H2O2 is one molecule of Hydrogen
Peroxide that has all of its atoms bonded together. Whereas, 2OH is two
molecules of OH bonded together.
10. Label the diagram with the names of each part or step:
Yields
Reactants
Na
Products
NaO
Coefficient
Subscripts
11. What do subscripts in chemical formulas tell you?
The number of atoms of each element that are in the formula
12. What do coefficients in chemical formulas tell you?
The number of molecules of a compound
13. What are the main six indicators/evidence that a chemical reaction has
occurred?
Precipitate forms
Gas is formed
Light is produced
Temperature change
Odor change
Color change (sometimes
14. Explain why a color change when two or more substances are mixed together,
does not always indicate a chemical change.
Color change can also be a physical change - for example, mixing
kool-aid in water. It is an expected color change. It is a chemical change
only when it is unexpected- for example mixing two clear liquids and having
the substance turn blue.
15. In a chemical reaction, what happens to the elements?
Elements that are combined chemically go through a reaction and are
rearranged into new substances
16.
17.
A chemical change produces a new ____substance______ whose properties
are ____different____compared to the properties of the reactants.
Some students conducted an investigation in which they added four different
solid substances to separate beakers of water. They stirred the mixtures for
one minute and then recorded their answers in this data table:
Which substance most likely caused a new substance to be formed when
mixed with water? Explain why you chose your substance.
Substance 2, bubbles were formed. This is evidence of a probable chemical reaction
18. How many atoms are represented in this formula? Write your answer on the
blank.
P4S3 = ___ There are 4 P, 3 S, so 7 atoms in all
19.
What is an endothermic reaction?
A chemical reaction that absorbs or uses energy, usually in the form of
heat (temperature drops)
20. What is an exothermic reaction?
A chemical reaction that gives off or expels energy, usually in the form
of heat (temperature increases)
21. Look at the graphs. Explain what each graph is representing and how the lines
show energy changes.
Endothermic:
Left graph – shows that the
energy is being absorbed –
when you look at the data
line, the products have more
energy than the initial
reactants
Exothermic:
Right graph – shows that the energy is being released – when you look at the data
line, the products have less energy than the initial reactants
22.
A student mixes two unknown substances together and observes what
happens. What evidence is shown that a chemical reaction may have
occurred?
Two liquids were combined and in the second picture solid particles are seen. The is
a precipitate that has formed from the mixing of two liquids
23. How do you know that when iron is exposed to air, the result is a chemical
reaction?
When iron is exposed to air (or water for that matter) it reacts with the
oxygen molecules. This reaction has a new substance as the product, known
as rust. Chemists call it iron oxide or ferric oxide. (Fe2O3)
24. Which equation shows that the total mass during a chemical reaction stays
the same? Circle the correct one.
2Na + 2H20
NaOH + H2
H2 + O2
H2O
Mg + Cl2
MgCl2
25. In a chemical reaction, the elements and numbers of each atom remain the
same. If this true, what must also be true about the mass (grams)?
The mass must also be the same on both sides of the chemical reaction
26. What elements are in an organic compound? ____carbon and
hydrogen______
27. What are physical properties?
Physical properties can be observed or measured without changing the
composition of matter.
28. List at least 5 physical properties
Physical properties can include: appearance, texture, color, odor,
melting point, density, solubility, polarity, etc.
29. Explain why a “state of matter” change is NOT evidence of a chemical
reaction.
When a state of matter change occurs, it is usually because there is an
increase or decrease of heat. Think about a chocolate bunny. If you leave it out in
the sun, it melts. But if you had it on a plate, you could, in theory, put the plate of
melted chocolate in the fridge and it would form back into a solid. The shape would
have changed, but it is still chocolate!!
More to the point, no new substance was made, no other
evidences of a chemical reaction is shown. Use what you know to logically
work each of these problems!!
Examples of state of matter changes (These are NOT chemical reactions!)
Water – liquid to solid to water vapor (steam)
Aluminum – we can shape it into a soda can, melt it, freeze it, but it is
still aluminum!
Lava – molten rock, solid rock
Study Tips and Reminders
1. Complete this test review and then study!
2. Text book pages that relate to this material:
Unit 3 – p. 109 – 135 and 139 – 168 (the second half of the unit
focuses on the second half of Unit 3 in the textbook)
3. Notes are always posted on the website – look in Unit 2.2
4. Remember, the “Unit Enrichment and Review” section at the bottom of
every unit has even more videos and links.
5. The labs and their concepts turn into questions on the test! Take a
look at the chemical reactions lab and notice evidences that a chemical
reaction has occurred.
6. Main concepts:
Know how read a chemical formula – what do the subscripts and
coefficients mean? How can you tell which elements are present.
Know the Law of Conservation of Mass and how it is applied to
chemical reactions
Know what makes a compound organic or not
Know the difference between physical and chemical properties
and changes
Exothermic and endothermic reactions
Know how to recognize what a balanced equation looks like