Name:____________________________________ Period:____
Date:__________________
Unit 4 Review
TEK: 8.5D - Recognize that chemical formulas are used to identify substances and determine the number of
atoms of each element in chemical formulas containing subscripts.
2Ca + O2  2CaO
1. In the equation above, how many atoms are present in one molecule of oxygen? _______
2. In the equation above, calcium and oxygen are the ___________________, and calcium oxide is the
___________________ . The ______________ in the middle of the equation means yields.
(word
bank: arrow, products, reactant)
Rusting occurs when iron is exposed to oxygen. The chemical equation for the rusting iron reaction is:
4Fe + 3O2  2Fe2O3
3. How many molecules of oxygen are required to make 2 molecules of Fe2O3? _______________________
Explain:________________________________________________________________________________
4. How many atoms of oxygen are required to make 2 molecules of Fe2O3? ___________________________
Explain:________________________________________________________________________________
5. If 4 atoms of iron can produce 2 molecules of Fe2O3 , then predict how many molecules of iron would be
needed to produce 6 molecules of Fe2O3 . Explain:_____________________________________________
Use this chemical reaction to solve questions 6-10:
Mg(NO3)2 + 2Na  2NaNO3 + Mg
6. How many atoms of oxygen are in one molecule of Mg(NO3)2? ___________
Explain:________________________________________________________________________________
7. How many atoms of oxygen are in 2 molecules of NaNO3? ___________
Explain:________________________________________________________________________________
TEK: 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. Explain the Law of Conservation of Mass in your own words:___________________________________
____________________________________________________________________________________ .
9. In a chemical equation, what must be true in order for the equation to support the Law of Conservation of
Mass?_________________________________________________________________________________
10. There are ______ atoms of nitrogen in the reactants and _______ atoms of nitrogen in the products.
Does this information support the Law of Conservation of Mass? Why/why not?____________________
______________________________________________________________________________________
Name:____________________________________ Period:____
Date:__________________
Unit 4 Review
11. Tell whether the equation is balanced or unbalanced and whether is supports or does not support the Law
of Conservation of Mass.
A. 2Fe2O3 → 3O2 + 4Fe (Balanced / Unbalanced) (Does / Does Not) Support the Law of Conservation of Mass
B. 3O2 +4 Fe → 2Fe2O3
(Balanced / Unbalanced)
(Does / Does Not)
Support the Law of Conservation of Mass
C. 4Fe → 3O2 + 2Fe2O3
(Balanced / Unbalanced)
(Does / Does Not)
Support the Law of Conservation of Mass
12. Which of the following is a true statement? Rewrite any false statement to be a TRUE statement.
A. The elements and the number of atoms of each element present in a chemical formula are used to
identify substances. True / False ________________________________________________________
B. Coefficients are used to identify substances. True / False __________________________________
____________________________________________________________________________________
C. Chemical formulas are used to identify substances. True / False _____________________________
____________________________________________________________________________________
D. Subscripts are used to identify substances. True / False ___________________________________
____________________________________________________________________________________
13. Which reaction is best represented by the model to
the right?
A. O2 + 2Ca  2CaO C. 2H2 + C  CH4
B. 4N + 2Ca 2CaN2 D. Na + Cl2NaCl2
14. Identify at least 2 limitations to the model in question #13.______________________________________
_______________________________________________________________________________________
TEK: 8.5E - Investigate how evidence of chemical reactions indicates that new substances with different
properties are formed.
15. Describe the evidence of a chemical reaction during the demonstration of the reaction between baking
soda and vinegar. What happened? What gas was formed?____________________________________
______________________________________________________________________________________
16. Limestone in the Earth’s crust has a chemical formula of CaCO3. It is made of calcium, carbon and oxygen.
Why can’t we breathe the oxygen in limestone? ______________________________________________
_______________________________________________________________________________________
Name:____________________________________ Period:____
Date:__________________
Unit 4 Review
Water temperature before
Water temperature after
the reaction (C)
the reaction (C)
100
25
26
20
100
25
38
25
100
25
50
30
100
25
????
Iron Mass (g)
Water Volume (ml)
15
17. Data from a recent study is shown above. Predict the temperature after the reaction when 30g of Iron are
used. ______________ Explain:_____________________________________________________________
18.
An experiment has been conducted using 3 substances. The
final temperatures are shown to the right. If researchers are
interested in using a sample with the lease amount of
temperature change during the experiment, which sample
would they choose? _______________ Show work below.
Sample
A
B
C
Initial
temperature
27 C
15 C
23 C
Final
temperature
Change in
temperature
19. Which of the models below correctly represents a molecule of Al2S3? Explain your choice. ____________
_______________________________________________________________________________________
A.
B.
C.