Miss GS 3/15/12
Energy Changes
A.
Purpose:
The purpose of this experiment was to
study how the energy of a solute and solvent changes when solutes dissolve in
solvents. A solute is a substance being dissolved in a substance, while a
solvent is the substance that the solute is being dissolved in. When a solute
and a solvent are mixed together, a solution is created. Solutes are not always solids and solvents
do not have to be liquids (Wile).
In order for a substance to dissolve in
a solvent, the solute must be broken down.
Ionic compounds do not have chemical bonds, thus the only thing holding
the ions together is their electronic attraction. When ionic solutes dissolve in a solvent, the
molecules of the solvent force their way between the ions and pull the ions
apart. Some ionic solids cannot dissolve
in certain solvents, due to the strong attraction between ions. When a compound cannot dissolve in a
substance, the compound is insoluble to that substance. Unlike ionic compounds, polar covalent
compounds are bonded together because the atoms of the molecule share
electrons. Nevertheless, since polar
covalent compounds have fractional charges, they can be dissolved like ionic
compounds. The only difference is that
in polar covalent compounds, the molecules dissolve as individuals, instead of
being pulled apart.
Liquid solutes are more easily dissolved
in solvents than solid solutes, because the molecules are not as tightly pack
as a solid. With gas solutes, the
molecules actually have to be brought closer together to dissolve. Purely covalent compounds do not dissolve
very well in polar covalent solvents.
This is because they do not have electrical charges, thus purely
covalent compounds can only dissolve in other purely covalent compounds
(Wile).
There is a limit to how much of a solute
can dissolve in a solvent. The term used
to describe the maximum amount of solute that can dissolve in a solvent is
solubility. Solubility depends on the identity of the solute and the identity
of the solvent. Also, physical changes
can also affect the solubility of a solute.
With solid solutes, the solubility increases with increasing
temperature, while the solubility of liquid solutes is not affected by
temperature change. Gas solutes actually
decrease in solubility with increasing temperature. Also, gas solutes are the only solutes that
are affected by pressure changes, increasing in solubility with increased
pressure. The solubility of liquid and solid
solutes is not affected by pressure (Wile).
When a solute dissolves in a solvent,
there is an energy change that occurs.
Chemical reactions can release energy in the form of heat, light, or
even sound. When a reaction releases
energy, it is an exothermic reaction.
These reactions can happen spontaneously and usually result in a
temperature rise. Other chemical
reactions absorb energy. Those reactions
are endothermic reactions. Endothermic
reactions cannot happen spontaneously and usually result in a temperature drop
during the reaction. An example of an
endothermic reaction is photosynthesis. In photosynthesis, plants take energy
from the sun to make glucose and oxygen (Helmenstine). An example of an exothermic reaction is
combustion reactions. All combustion
reactions are exothermic, and it usually needs an amount of energy to start the
reaction, such as lighting the wood with a match to get a fire started
(eNotes.com).
This experiment hopes to show an example
of a solute releasing heat when dissolved in a solvent. A solution can either have an exothermic
process or endothermic process. If a
solution increases in temperature, an exothermic process happened. On the other hand, if a solution decreases in
temperature, an endothermic process happened. Most solids dissolve endothermic,
meaning they absorb energy to dissolve in the solvent (Wile).
This topic is of interest to science
because scientist experiment with solutes and solvents all the time. Also,
since substances either release heat or absorb heat when dissolved in a
solvent, there are practical applications of this phenomenon that can be used
in common every-day life. One example is
cold packs. When the two substances in
the bag interact, it creates an endothermic process which then cools down the
solution considerably, providing an excellent substitute for ice (Wile). Exothermic reactions are very important to
fire and explosion investigations. In such
investigations, the substances involved and how each react with one another is
important in finding what kind of chemical reaction occurred and caused the
fire (eNotes.com).
Hypothesis: If water is added to the
powdered drain cleaner, then a reaction which causes a temperature change will
occur.
B.
Equipment:
1.
A beaker
2.
Powdered drain cleaner
3.
Rubber gloves
4.
Water
5.
A kitchen sink
6.
A tablespoon
7.
Safety goggles
C.
Procedure:
1.
Put the gloves on.
2.
Measure out 3 tablespoons of powdered drain cleaner into the beaker.
3.
Put the beaker in the sink directly under the faucet.
4.
Turn the water on slowly so that the water from the faucet begins to
fill the beaker. Add enough water so
that the water level in the beaker in about one centimeter above the powdered
drain cleaner.
5.
Stir the solution with the tablespoon.
6.
Take one glove off and carefully touch the outside of the beaker, near
the bottom. Most likely, the beaker will
feel warm. It might be quite hot, so be
careful.
7.
Continue to stir the solution with the other hand, and periodically
touch the outside of the beaker near the bottom to see how hot it is
getting. Once again, be careful when
touching the beaker with bare hands, as it can get very hot.
8.
Eventually, the solution might get so warm that the beaker can no longer
be comfortably touched. At that point,
put the glove back on.
9.
Turn on the cold water, allowing it to fill and overflow the
beaker. Keep
the water running for several minutes, allowing a large amount of the powdered
drain cleaner to be flushed down the drain.
10.
Tip the beaker over and rinse it out.
11.
Clean up the mess.
D.
Observations:
1.
Rubber gloves were put on, according to the procedure.
2.
Then, 3 tablespoons of powdered drain cleaner were measured into the
beaker.
3.
The beaker was then placed in the kitchen sink directly under the
faucet.
4.
Being careful to turn the water on slowly,
enough water was added to the beaker until the water level was about one
centimeter above the powdered drain cleaner.
The water began to bubble as the powdered drain cleaner started to react
with the water.
5.
Using the tablespoon, the solution was mixed. The water became cloudy with a bluish tint,
and the bubble became bigger. Also,
steam was rising from the beaker and there was a slightly intolerable smell.
6.
One glove was taken off, and the beaker was felt, near the bottom. The beaker felt hot, yet it was not
uncomfortable to touch the beaker.
7.
Continuing to stir the solution, the beaker was periodically touched,
near the bottom, to feel how hot it was becoming. After about seven seconds, the beaker was too
hot to be comfortably touched.
8.
The glove was put back on and cold water was allowed to fill and
overflow the beaker for a minute, allowing the powdered drain cleaner to be
washed down the drain of the kitchen sink.
9.
The beaker was rinsed, dried and put away.
E.
Conclusions:
The hypothesis was supported. When the
water and the powdered drain cleaner mixed, the resulting solution created a
reaction that created a temperature change.
The powdered drain cleaner was the solute while the water served as the
solvent. Upon mixing the solute and the
solvent, the solution produced a reaction which caused the solution to heat
up. Thus, when powdered drain cleaner is
dissolved in water, it causes a reaction, an endothermic reaction, where heat
is produced.
One way for improvement for this
experiment is to be more careful when adding the water. This would help avoid any experimental errors
which would occur if too little water or too much water was added. Another idea for improvement could be to stir
the solution better. This would make sure
that all of the powdered drain cleaner reacts with the water, thus enhancing
the results of the experiment.
In relationship to this topic, one idea
for further research could be to research other exothermic and endothermic
reactions. One could try experimenting
with other substances to see the energy change created, either exothermic or
endothermic. Another idea for further
research could be to talk to a chemist and maybe watch the chemist perform an
exothermic or endothermic reaction using certain chemicals or gases. In addition, one could try visiting a fire
investigator and see how the investigator discovers the causes of fires.
F.
Bibliography:
“Exothermic Reactions” eNotes.com 2012
March 16, 2012
Domain: www.enotes.com/
Document: exothermic-reactions-reference/exothermic-reactions
Helmenstine,
Anne Marie “Endothermic and Exothermic Reactions” 2012 March 16, 2012
Domain: chemistry.about.com/
Document: cs/generalchemistry/a/aa051903a.htm
Rosenoff, Steven. Classroom/Internet Lecture.
March 9, 2012.
Wile, Dr. Jay L. Exploring Creation with
Chemistry, 2nd Edition. Apologia
Educational Ministries, Inc. 2003