Introduction: indirectly, as, when the reaction occurs,

Introduction:
The purpose of this lab is to investigate reaction rates, in this case,
the investigation of effect of reactant concentration on reaction rate, as many
reactions occur at different rates, in this experiment the factor investigated
will be how the concentration of one of reactants in the system, affects the
rate of reaction. In the experiment designed for this observation, the rate of
reaction is investigated indirectly, as, when the reaction occurs, the solution
turns white and what is observed is the time in seconds it takes the reaction
to turn fully white (opaque) by observation of a black cross drawn under the
transparent container in which the reaction takes place.
The prediction/hypothesis in this experiment is based on the collision theory:
The time it takes for the reaction to occur is dependent on concentration of
one of the reactants, lowering the concentration, will increase the time needed
for the reaction to be fully complete.

 

Research
Question:
How does the concentration of a reactant affect the reaction rate?

We Will Write a Custom Essay Specifically
For You For Only $13.90/page!


order now

 

Variables
in the experiment:
This experiment is designed around the observation of the reaction
becoming opaque and how the concentration of one of the reactants affects the
rate at which the reaction becomes opaque, as the concentration is the variable
which Is changed, it is determined the independent variable, as the
concentration changes, the rate at which the reactions turns opaque, and at
which the cross drawn underneath it “disappears” is expected to change, therefore
the rate of reaction/time for the cross to disappear is deemed the dependent
variable is this experiment as the reaction rate is expected to depend on the
concentration, the variables which are controlled is the experiment are: the
initial temperature of the solution, the volume of the acid added and the total
volume of the solution, the control of initial temperature allows us to
determine if the temperature may have had an impact on the experimental outcome.
Control of the total volume and acid added volume is needed to assure that the
independent variable is affecting the dependent one. The temperature is
controlled by a thermometer, the volume is controlled by accurate measurement
of the substances used and diluent (in this case water – H2O) used.

Independent: Concentration, Dependent: Time for the cross to disappear,
reaction rate
Controlled: Total volume, initial temperature, volume of HCL added.

 

Background
Information:
Collision Theory:
“For a reaction to occur, particles must collide; with more than a certain
minimum of energy and with correct orientations”; “With more particles in a
certain volume, the particles collide more often (collision frequency is
higher) and therefore there is a greater chance of a successful collision (i.e
one that results in a reaction) occurring in a certain time” 1
according to collision theory, only a certain amount of particles react when
colliding, therefore reactions happening at different rates, collision theory
also explains a phenomenon; reaction rate tends to increase with the
concentration of the reactants. The reason being, a higher concentration of
particles, increases the chance of the particles colliding, therefore
increasing the reaction rate. 

In the experiment, Na2S2O3 and HCL are
used, when reacted together, sulfur is produced as a solid precipitate, and it
is the chemical which makes the solution become increasingly cloudy, therefore
allowing the measure of time taken for the reaction to become opaque.

To investigate the relation between the concentration of Na2S2O3 and
time taken for the reactants to become opaque, the Na2S2O3
will be diluted with water (H2O) to achieve different
concentrations of the Na2S2O3 solution, each
concentration will be used in 3 trials, to assure the accuracy of the experimental
outcome.

The balanced chemical equation in this experiment is:
Na2S2O3(aq)
+ 2HCL(aq) à 2NaCl(aq) + SO2(aq)+H2O(l)+S(s)

Experimental
Equipment:

Equipment

1.      Graduated Cylinder ±0.5ml

2.      Graduated Cylinder ±0.2ml

3.      Conical flask (Container)

4.      Stop Clock ±0.2s

5.      Digital thermometer ±0.1 °C

6.      Pipettes

7.      Funnel

8.      Paper + Pen

Chemicals

1.      Hydrochloric acid HCL(aq)
Conc. 2M

2.      Sodium thiosulfate Na2S2O3
Conc. 0.25M

3.      Distilled water H2O

 

 

Safety
Notes:
HCL: Hydrochloric
Acid – Corrosive, prolonged inhalation and skin exposure of the acid at high
concentrations can be dangerous, therefore good ventilation and the use of
gloves is recommended.

Na2S2O3:
Sodium thiosulfate – Prolonged inhalation and skin exposure at high
concentration can be dangerous, good ventilation and use of gloves is
recommended, additionally when in fire, produces dangerous fumes, therefore it
is recommended to avoid contact with high temperatures.

Both HCL and
Na2S2O3 bear low risk disposal hazards,
although after reacted, the created solid should be filtered out of the liquid
and disposed into appropriate container.

There is no ethical issues regarding this experiment.

 

 

 

 

 

 

 

 

Diagram of lab set-up:

 

 

 

 

 

Conical
Flask + distilled Na2S2O3

 

 

 

Graduated Cylinder + HCL

 

 

Procedure:

1.      The mixtures of various
concentrations of sodium thiosulfate are prepared.

2.      Na2S2O3
is placed in a conical flask, diluted with H2O to a desired
concentration.

3.      5ml of 2mol/l HCL is added, and the
conical flask is agitated to ensure mixing of the reactants.

4.      The time for the cross to disappear
is recorded

5.      The experiment is repeated with different
Na2S2O3 concentrations, until desired amount
of trials is reached.

Methods
(Anticipated problems & Methodology notes):

Initially the agitation was attempted to be done by a
stirring rod, but the method was quickly abandoned as the conical flask used
was too small, causing the stirring to be overly difficult, the used method was
a quick “circular” motion agitation of the conical flask, the agitation was
done in the same manner in every experiment to assure that the agitation did not
cause different experimental outcomes than previous trials.
The use of magnetic stirrer was suggested during the lab, but the idea was
quickly abandoned, due to experimental method focusing on observation of a
cross which was drawn under the conical flask, a magnetic stirrer would have
made it extremely hard to estimate if the cross was still visible at the lower
concentrations of Na2S2O3.

During the experiment, effort was made to decrease any
chances of liquid droplets staying on the side of the conical flask when HCL
was added to the flask, and the liquids were poured at a slow pace to decrease
the chances of additional air bubbles appearing in the measuring
cylinders. 

In dilution 5 the volume of sodium thiosulfate used was
changed from 2mL to 3 mL as it has proven to be too difficult to measure out
the 2mL with the used measuring cylinder, to assure that the same measuring
cylinder was used during the whole experiment, 3mL was used instead, and the
amount of diluent was also increased by 1mL, to assure equal ratio between 2mL
sodium thiosulfate and 18mL diluent (water, and 3mL sodium thiosulfate and 17mL
of diluent.

As the stop clock used was operated by the same person
watching for the cross to disappear, an uncertainty of ±0.2s was assigned the
acquired time data, to account for human reflexes and reaction time.

Raw Data:  
Quantitative Data + (Lab Notes):

During the experiment, the same person was used as the
observer & timekeeper, and the same person agitated the solution, to assure
that the method is repeated in as close manner to other trials as possible.

During the first trial of dilution no.1 it was determined
that the agitation method had to be changed, as the conical flask was too small
to agitate the mixture with a stirring rod, therefore the trial data was
discarded, and trial 1 was repeated, this time the whole conical flask was
shaken in a “circular” motion to achieve the desired agitation.

In all trials the conical flask used was of the same brand
and model, to ensure the same volume and “thickness” of the liquid in the
conical flask, therefore the visibility of drawn cross.

During Dilution no.1 Trial 2, the used thermometer has
changed, due to fact that the digital display was scratched and proved to be
hard to read.

During Dilution no.4 Trial 3, the recorded time was
approximately 2-4 seconds after the cross has disappeared, due to the
timekeeper missing the stop button on the stop clock.

During Dilution no.5 only two trials were conducted as each
trial has taken approximately 10 minutes, and the lab time was limited.

Quantitative
Data:

Dilution no.

V(Na2S2O3) / ±0.5 mL

V(H2O) / ±0,20 mL

Vtotal after mixing / ±
mL

V(HCl) ±0,20 mL

1

20

0

25

5

2

15

5

25

5

3

10

10

25

5

4

5

15

25

5

5

3

17

25

5

 

Dilution no. 1

Trial no.

Time for mark to disappear /  ± 0.2 s

T / 
± 0.1 °C

1

28.3

18.5

2

29.0

21.8

3

28.4

21.8

 

Dilution no. 2

Trial no.

Time for mark to disappear /  ± 0.2 s

T / 
± 0.1 °C

1

39.1

21.5

2

39.6

21.4

3

41.8

21.2

 

Dilution no. 3

Trial no.

Time for mark to disappear /  ± 0.2 s

T / 
± 0.1 °C

1

70.1

21.6

2

64.4

21.1

3

64.5

21.3

 

Dilution no. 4

Trial no.

Time for mark to disappear /  ± 0.2 s

T / 
± 0.1 °C

1

149.4

21.3

2

150.7

21.5

3

152.5

21.6

 

Dilution no. 5

Trial no.

Time for mark to disappear /  ± 02 s

T / 
± 0.1 °C

1

612.78

21.6

2

611.71

21.6

 

1
Owen, S. (2014), Chemistry for the IB Diploma Second Edition, Cambridge
University Press, United Kingdom, pages 246-247

Go Top
x

Hi!
I'm Rita!

Would you like to get a custom essay? How about receiving a customized one?

Check it out