A 1.0 g sample of an alkaline earth metal M reacts completely with 0.8092 g of chlorine gas to yield and ionic salt with the formula MCl2. In the process 9.46 kJ of heat is released.

1
A 1.0 g sample of an alkaline earth metal M
reacts completely with 0.8092 g of chlorine gas
to yield and ionic salt with the formula MCl2.
In the process 9.46 kJ of heat is released.
What is the molecular mass and identity of the
metal M?
M Cl2 MCl2
1 mol of M reacts with 1 mol Cl2
0.8092g/71g/mol 0.0114 mol
1 g M/gAt Wt M 0.0114 mol
M 87.7 g/mol
A check of the periodic table reveals that M is?
Sr
If 9.46 kJ/mol of heat was released, how much
heat would be released if 1 mol of SrCl2 was
formed?
-9.46 kJ/g 87.7 g/mol -829.6 kJ/mol
2
Sodium nitrite, NaNO2, is frequently added to
processed meats as a preservative. The amount of
nitrite in a sample can be determined by reducing
the nitrite to nitric oxide (NO) in acid with
excess iodide which forms I3- and the titrating
the I3- liberated with thiosulfate (S2O3-2) to
form iodide ion and S4O6-2. When a nitrite
containing sample of meat (2.935g) was analyzed,
18.77 mL of 0.15 M Na2S2O3 solution was needed
for the analysis. What is the mass percentage of
sodium nitrite in the meat sample?
NaNO2 I- NO (g) Na I3-
oxidation state of N in NaNO2?
3
In NO?
2
oxidation state of I-?
-1
In I3-
-1/3
e- NaNO2 2H NO(g) H2O Na
reduction
3I- I3- 2e-

oxidation
2NaNO2 4H 3I- 2NO(g) 2H2O I3- 2
Na
3
2NaNO2 4H 3I- 2NO(g) 2H2O I3-
2Na
Titrating the I3- liberated with thiosulfate
(S2O3-2) forms iodide ion and S4O6-2.
In I- ?
-1
oxidation state of I3-?
-1/3
oxidation state of S in S2O3-2?
2
In S4O6-2 ?
2.5
I3- 2 e- 3I-
2S2O3-2 S4O6-2 2 e-
2S2O3-2 I3- S4O6-2 3I-
4
2NaNO2 4H 3I- 2NO(g) 2H2O I3-
2Na
2S2O3-2 I3- S4O6-2 3I-
When a nitrite containing sample of meat (2.935g)
was analyzed, 18.77 mL of 0.15 M Na2S2O3 solution
was needed for the analysis. What is the mass
percentage of sodium nitrite in the meat sample?
How many mols of sodium thiosulfate was
consumed?
0.01877 L 0.15 M 0.0028 mol Na2S2O3
How many mol of I3- must have been present?
0.0014 mol I3-
Therefore 0.0014 mol of I3- must have been
produced in the first reaction
How many mol of NaNO2 are needed to produce
0.0014 mol I3-?
0.0028 mol NaNO2
MW NaNO2 69 g/mol
0.0028 mol NaNO2 69 g/mol 0.193g
0.193/2.935100 6.6
5
Photochromic glasses which darken on exposure to
light, contain a small amount of silver. When
irradiated with light, the silver ion is reduced
to silver metal by capture of an electron from
chlorine to produce a chlorine atom and the glass
darkens. The chlorine atom formed is prevented
from diffusing away by the glass. When the light
is removed, the silver metal loses an electron
and silver chloride is reformed. If 310 kJ/mol of
energy is necessary for the reaction to proceed,
what wavelength of light is necessary?
310 kJ/mol/6.021023 atoms/mol 51.510-23
51.510-20 J/atom
E h? 51.510-20 J/atom 6.6310-34 Js ?
3108 m/s ??
? 7.771014 s-1
3108 cm/s ?7.771014 s-1
? 3.8610-7 m 109 nanometers/m
? 386 nm
6
386 nm
7

• Three atoms have the following electronic
  configurations
• 1s22s22p63s23p1
• 1s22s22p63s23p5
• 1s22s22p63s23p64s1
• Which of the three has the largest Ei1?
• Which of the three has the smallest Ei4?

Al
Cl
K
Cl
Cl
8
A 0.053 g sample of an alkali metal was burned in
air to give a mixture of oxide (M2O) and nitride
(M3N). The reaction product was dissolved in
water according to Rx 1 and 2 and titrated with
0.1M HCl requiring 96.8 mL for complete
neutralization. What is the metal and composition?
Rx 1 M O2 M2O Rx 2
M N2 M3N
Rx 1 M2O H2O MOH
Rx 2 M3N H2O MOH NH3
HCl MOH NH3 MCl H2O NH4Cl

What is the first thing to do?
balance the equations!
Rx 1 4M O2 2M2O
M 1/4O2 1/2M2O
1/2M2O 1/2H2O MOH
MOH HCl MCl H2O
Rx 2 6M N2 2M3N
M 1/6N2 1/3 M3N
1/3M3N H2O MOH 1/3NH3
MOH 1/3NH3 4/3HCl MCl 1/3NH4Cl H2O
9
A 0.053 g sample of an alkali metal was burned in
air to give a mixture of oxide (M2O) and nitride
(M3N). The reaction product was dissolved in
water and titrated with 0.1M HCl requiring 96.8
mL for complete neutralization according to the
following two reactions.
Rx (1)with oxygen 1 mol of M reacts with
1 mol of HCl
Rx (2)with nitrogen 1 mol of M reacts
with 4/3 mol of HCl
Amount of HCl consumed to endpoint
0.0968 L0.1M 0.00968mol
How much HCl would be required if M is
Li only Rx 1 occurs
only Rx 2 occurs
0.053/6.9 0.00764 mol Li
0.07641 0.00764 mol
0.07644/3 0.01019 mol
How much HCl would be required if M is
Na only Rx 1 occurs
only Rx 2 occurs
0.053/23 0.0023 mol Na
0.0023 1 0.0023 mol
0.0023 4/3 0.0031 mol
10
A 0.053 g sample of an alkali metal was burned in
air to give a mixture of oxide (M2O) and nitride
(M3N). The reaction product was dissolved in
water and titrated with 0.1M HCl requiring 98.6
mL for complete neutralization according to the
following two reactions.
Rx (1)with oxygen 1 mol of M reacts with
1 mol of HCl
Rx (2)with nitrogen 1 mol of M reacts
with 4/3 mol of HCl
Amount of HCl consumed to endpoint 0.0986L0.1
0.00986 mol
How much HCl would it take if Rx 1 and Rx 2
contributed equally?
0.5.007640.50.01019 0.00891 mol
compared to 0.00968mol
let a be the fraction reacting by Rx 1
a(0.00764) (1-a)(0.01019) 0.00986 a 0.
148 or 14.8 by Rx1