Download sig figs, atoms and ions KEY

Chemistry 139
Clark College
Name: _____________________________________________
HW 2: sig figs, equations, ions and atoms
Don’t forget to use correct significant figures and units.
1. For the following problems – perform the mixed operations. Remember – use the
addition/subtraction sig fig rule for +/ - and the multiplication/ division rule only for those
operations!
a. (23.4 – 21) / 15.678 = ______0.1___________
(2/15.678) or even if you carry through 2.4/15.678 remembering final answer can only have
1 sf you will get 0.1 or 0.15 which rounds to 0.2 – so either is acceptable
b. (1.567 + 99.2) x 15 = _______1.5 x 103_____________
100.8 x 15 (2 sf number) = 1512 = 1.5 x 103 if you used the whole number 100.767 x 15 =1512
also. So same answer to 2 sf (2 sf because of 15)
c.
(95.78 + 6.8931) x 34.5667 = ____3549.0___________
102.67 from addition!! (5 sf) x a 6 sf number so final answer has 5 sf)
d. (95.78 – 92.78) x 3.125 = ____9.38___________
3.00 (3 sf number) x a 4 sf number, final answer has 3 sf
2. Rearrange the following equations for the variable listed:
a. D =
m
v
solve the equation for v =
b. P V = nRT solve the equation for T =
Chapter 2 Homework
v=
T=
m
D
PV
nR
Page 1 of 4
3. Fill in the table below: make sure that you list the numbers of protons, neutrons, and electrons for
each species:
24Mg
23Na
70Ga
12 protons
__11____ protons
__31____ protons
___12___ electrons
11 electrons
31 electrons
__12____ neutrons
__12____ neutrons
39 neutrons
35Cl
35Cl-1
56Fe
17 protons
17 protons
__26____ protons
___17___ electrons
__18___ electrons
26 electrons
___18___ neutrons
__18____ neutrons
___30___ neutrons
56Fe+3
39K
39K+1
__26____ protons
___19___ protons
__19____ protons
23 electrons
__19___ electrons
__18___ electrons
___30___ neutrons
20 neutrons
20 neutrons
32S
32S-2
48Ti
__16____ protons
__16____ protons
___22___ protons
__16___ electrons
__18___ electrons
__22___ electrons
___16___ neutrons
__16____ neutrons
__26____ neutrons
4He
31P
31P-3
___2___ protons
___15___ protons
__15____ protons
___2___ electrons
__15____ electrons
__18___ electrons
___2___ neutrons
___16___ neutrons
___16___ neutrons
4. Circle the charge that would be formed from the following species IF they formed an ion (HINT:
for the last four you might want to check the class notes!)
Species
Ion charge(s)
Na
+1
Ca
+2
Ba
+2
N
-3
S
-2
I
-1
P
-3
5. Complete the following table pairing up the ions to form a neutral compound: (hint: fill in the
charges first!)
IONS
Cl-__1__
S-__2__
N-__3__
Na+_1__
NaCl
Na2S
Na3N
Ca+_2__
CaCl2
CaS
Ca3N2
Al3
AlCl3
Al2S3
AlN
6. Calculate the molecular mass/molar mass for each of the following?
a. AlP
Al: 1 x 26.98 = 26.98 grams/mol
P 1 x 30.97 = 30.97 grams/mol
Sum: 26.98 + 30.97 =
57.95 grams/mol
b. Al2O3
Al: 2 x 26.98 = 53.96 grams/mol
O 3 x 16.00 = 48.00 grams/mol
Sum: 53.96 + 48.00 =
101.96
grams/
mol