STE
Pretest 2.2 Solutions
1.
Some nuclear reactions are shown below, all of which occur in the sun.
a)
Write an equation for
each reaction.
1
1
H
1
1
2
1
2
1
H
1
1
3
2
3
2
b)
c)
He
H
H
0
1
H
e
He
3
2
He
4
2
He 211H
Does any of the above
reactions create
an alpha particle?
Yes = 24 He
A positron?
Yes = 10 e
d)
How does fusion cause the sun to shine?
Mass gets destroyed and converted into energy.
2.
Give three natural sources of radioactivity in your home.
Potassium 40 in people, food etc.
Cosmic rays (released by stars, especially exploding ones)
Radon from uranium in the earth
3.
Compare the number of neutrons and protons in Cs and Ba. What particle
from the nucleus of Cs is being transformed in the creation of the beta
aprticle?
137
55Cs
→
137
56Ba
+ e− + νe
Cs has 55 protons and 82 neutrons(137-55), but Ba has one more proton
and only 81 neutrons, so 1 neutron has turned into a proton and a beta particle.
Don’t worry about the antineutrino(
4.
)
You just calculated that 3.0 g of LiCl are needed to make 250
ml of a solution. Convert to mol/L
3.0 g(mole/ 7 + 35.5 g) = 0.070 moles
C = n/V = 0.070 moles/ 0.250 L = 0.28 moles/L
5.
Ethyl alcohol (C2H6O)'s density is 0.7893 g/ml. If 35 ml of alcohol reacted
according to
3 C2H6O + 4 H2CrO4 + 12 HCl C2H4O2 + 4 CrCl3 + 13 H2O
a)
How many grams of HCl also reacted?
0.7893 g/ml * 35 ml = 27.63 g
27.63 g C2H6O (mole/46 g) = 0.600 moles C2H6O
0.600 moles C2H6O (12 HCl/3 C2H6O) = 2.40 moles HCl
2.40 moles HCl (36.5 g/mole) = 87.7 g
b)
If the concentration of HCl was 0.10 moles/L, how many mL of HCl
reacted with 0.600 moles of alcohol?
0.600 moles C2H6O (12 HCl/3 C2H6O) = 2.40 moles HCl
n = CV
2.40 moles HCl = (0.10 moles/L)*V
V = 2.40/0.10 moles/L
= 24 L = 24 000 mL
7.
How much more acidic is a pH = 6 solution compared to one at pH = 6.3?
=10-6/10-6.3 = 2
8.
What is the pH of a solution that has an H+ concentration of 0.01 moles/L?
pH= -log[H+]
-log[0.01] = 2
9.
What would happen if bacteria did not break down organic phosphate into
inorganic phosphate?
Plants would not be able to obtain P.
10.
What happens when there aren’t enough plants to absorb all the inorganic
phosphate from animal waste? Where does the phosphate go? Why is this a
problem?
It ends up in lakes and rivers where
excess phosphate leads to excess
growth of algae. This depletes
oxygen levels and depending on the
species of algae, it could lead to the
production of toxins in water.