# Unit 3 Review - Chemistry

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"Unit 3 Review - Chemistry"

```					Unit 3 Review - Chemistry                                   Name: ________________

Accuracy and Precision
Complete pg 10 in VG Workbook

1. Averages:
A – 10.29
B – 10.24
C – 12.04
D – 10.66

2. Percent error
A – 0.49%       (10.29 – 10.24) / 10.24   x 100
B – 0%
C – 17.6%
D – 4.1%

3. Average deviation – For each data point, find out how far it is from the average
Example for A:
Average for A was 10.29
Data points were 10.26, 10.30, 10.21, and 10.39
10.26 is 0.03 away from avg
10.30 is 0.01 away
10.21 is 0.08 away
10.39 is 0.10 away Avg of 0.03, 0.01, 0.08, and 0.10 is 0.0675

A – 0.0675
B – 0.46
C – 0.0175
D – 1.32

4. Best to worst accuracy (which students were closest to the right answer). This is
determined by who has the lowest % error.

B is best, then A, D, C is worst

5. Best to worst by precision (which students were the most consistent). This is
determined by who has the lowest average deviation.

C is best, then A, B, D is worst
Metal, Nonmetal, or Semimetal
Use the clues to determine if the following are metals (M), nonmetals (NM), or
semimetals (SM)

1. Malleable and conducts electricity M
2. Brittle and shiny SM – Brittle is like nonmetal, shiny is like a metal
3. Ductile and a good heat conductor M
4. Gas at room temperature NM
5. Sulfur NM
6. Cobalt M
7. Arsenic SM
8. Plutonium M
9. Dull and a good conductor of electricity SM
10. Usually solid at room temperature M
11. Gains electrons to be stable NM
12. Malleable and breaks down in acid M
13. Polonium SM
14. Fluorine NM
15. Technetium M
16. Samarium M

Percent Composition

17. What is the % of Br in MgBr2? 159.8/184.11 x 100 = 86.8%

18. What is the % of O in Al(OH)3? 48/78.01 x 100 = 61.53%

19. What is the % of S in Ga2(SO4)3? 96.21/427.65 x 100 = 22.5%

20. If you are mining for iron, what is a better source: FeO or Fe2O3? Show work.

FeO is a better source because it contains a higher % of Fe. Even though Fe2O3
appears to have more Fe, is has even more O which gets in the way.

FeO - 77.7% Fe         Fe2O3 – 69.9% Fe
Periodic Trends/Groups
Determine which atom is larger in size (not necessarily mass)
21. Mg or P         Mg – further to left, same number of shells, but fewer protons
22. S or As         As – further to bottom left, more shells
23. Li or He        Li – further to bottom left, more shells
24. Cr or Eu         Eu – further to bottom left, more shells (remember that the part of
the table where Eu is actually belongs in the part of the table where La and Ac are)
25. Mg or Mg2+      Mg – Mg has more electrons and so is bigger
3-
26. N or N           N3- - N3- has more electrons and therefore is bigger

Determine which atom is more reactive
27. Na or K          K – it’s a metal so further down and to the left on table is more
reactive (farther from boundary – also, K is larger and larger atoms lose electrons more
easily, which is how metals react)
28. P or O           O – it’s a nonmetal so further up and to the right is more reactive.
This makes it a smaller atom and smaller atoms gain electrons more easily, which is how
nonmetals react.
29. Fe or Cu       Fe – they’re metals and so further down and to the left is more reactive
30. S or He         S – Helium is “disqualified” because it is a noble gas and they don’t
react

Identify the element based on the clues
31) Element in third period with 4 valence electrons      Si
32) Metalloid in second period                            B
33)   Heaviest alkaline earth metal                        Ra
34)   4th period and forms –2 charge                      Se
35)   Alkali metal that is smallest in size            Li – H doesn’t count as alkali metal
36)   Halogen that is largest in size                    At
37) 5th period semimetal that is larger in size          Sb
38) Noble gas that is largest in size                    Rn
39) Lightest noble gas                                  He
40). Heaviest 3rd period element                       Ar (heaviest is not same as biggest
41) Largest transition metal                     Ac (or whatever metal is on the bottom
left of your table where the transition metals are – this can vary by table)
42) Smallest atom on table                                 He
43) Most reactive alkali metal                           Fr
44) Most reactive halogen                                F
45) Least reactive alkaline earth metal                 Be
46) Most reactive metal in 5th period                   Rb
Balancing Equations – Balance the following equations

47)       2   HgO         --->        2 Hg             +            O2

48)      8 H2S        +           8 Cl2       --->             S8         +        16       HCl

49)       SrBr2      +            (NH4)2CO3     --->           SrCO3           +        2       NH4Br

50)      Al2(SO4)3   +           3 Ca(OH)2     --->        2    Al(OH)3            +        3    CaSO4

51)    2 C6H14        +          19   O2        --->            12       CO2            +         14 H2O

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