Keeping the titration is when the solution just

Keeping up the standards

The purpose of this assignment is to undertake
titrations and colorimetry to determine the concentration of solutions. A key
part of the job will be making and testing standard solutions using colorimetry
and titrations. This will be carried out whilst making sure the equipment is
calibrated and also the equipment and chemicals are safety checked. I will also
be making and testing standard solutions using colorimetry and titrations.

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Colorimetry is a way to find the concentration
of coloured compounds in a solution by using a colorimeter; titrations are a
common lab method used as analysis in order to find an unknown concentration of
an element.

Titrations

Apparatus:

·        
Goggles

·        
Bench Mat

·        
100cm3 beaker

·        
250cm3 beaker

·        
250cm3 conical flask

·        
250cm3 bulb pipette

·        
Pipette filler

·        
Burette

·        
Burette stand and holder

·        
Plastic filter funnel

·        
White tile

·        
Teat pipette

·        
Access to: your standard sodium
carbonate solution dilute hydrochloric acid to standardise phenolphthalein
indicator solution methyl orange indicator solution

Method:

1.      Transfer
a 25cm3 portion of the sodium carbonate solution to a 250cm3 capacity conical
flask. Add a few drops of phenolphthalein indicator solution.

2.      Titrate
with the hydrochloric acid. The end-point of the titration is when the solution
just changes from pink to colourless. Note the titre, and then add a few drops
of methyl orange.

3.      Titrate
with the hydrochloric acid. The end-point of the titration is when the solution
just changes from yellow to red. Note the second titre.

4.      Repeat
steps 1-3 until they are the same or within 0.1 cm3. Tabulate your titrations
as described in The Burette sheet.
You will need two sets of tables.

5.      After
tidying away, do the calculations described overleaf.

Photographs of method:

 

 

 

 

    Step
1(HCl)                Sodium
Carbonate     Add phenolphthalein     Add methyl orange           Mix with HCl

Calculations:

Calculate the Mr of Na2CO3.

Ar(Na)=23 
Ar(C)=12  Ar(O)=16

Look back at the accurate mass of sodium
carbonate you used in the last practical. Using your answer to step 1,
calculate the No. of moles of Na2CO3 that you dissolved in 250cm3 of water
during Volumetric Analysis 1.

Using your answer to step 2 to calculate the
number of moles of Na2CO3 in the 25cm3 transferred to the conical flask.

Stage
1 – Phenolphthalein:

Na2CO3(aq)
+ HCL(aq)  NaHCO3(aq) + NaCl(aq)

M = 0.07*0.025 = 0.00175M

Ratio = 1:1

C = 0.0175/0.014525 = 0.11M

Stage
2 – Methyl Orange:

NaHCO3(aq)
+ HCl(aq)        NaCl(aq) + CO2(g) +
H20(l)

M = 0.0780.025 = 0.00175M

Ratio = 1:1

M = 0.0175/0.014525 = 0.11M

Results:

1. Phenolphthalein indicator (first part of
each run)

Burette reagent

Approx.  0.075M
hydrochloric acid

Conical flask

Standard sodium carbonate solution

Indicator

Phenolphthalein

 

 

Run 1

Run2

Run 3

Run 4

Final volume (cm3)

16

16

14.5

15.3

Initial volume (cm3)

0

0

0

0

 

2. Methyl orange indicator (second part of
each run)

Burette reagent

Approx.  0.075M
hydrochloric acid

Conical flask

Standard sodium carbonate solution

Indicator

Methyl orange

 

 

 

 

Run 1

Run 2

Run 3

Run 4

Final volume (cm3)

14.2

14.5

15

14.4

Initial volume (cm3)

0

0

0

0

 

Observation(s):

·        
Colour change volumes were recorded
when the colour change was strong and not when the colour was in transition of
changing and or faint.

·        
Colour changes to pink when you add
phenolphthalein on NaCl.

·        
Colour returns to uncoloured when you
add HCl.

·        
Colour changes to yellow when you add
Methyl orange.

·        
Colour returns to pink when HCl is
added.

Colorimeter

How
to operate a Colorimeter:

1.      Turn
the instrument on for at least 5 minutes before using it to allow it to
stabilize itself

2.      Use
the most appropriate filter for analysis and insert it into the light path

3.      Use
a clear solution and zero the instrument with it making sure the clear side of
the cuvette are in the lights path

4.      Place
your solution in the colorimeter and read the solutions absorbance. If the
absorbance is stated as ‘over range’ then the sample must be diluted so you can
receive a reading

5.      At
regular intervals, you can use the clear sample in order to make sure the
machine is still calibrated

Apparatus:

·        
Copper Sulphate

·        
Distilled Water

·        
Colorimeter instrument

Method:

1.     
After been given a solution of copper
sulphate (0.5M) you need to produce 5 different concentrations will be 0.0,
0.1, 0.2, 0.3 and 0.4M.

2.     
Fill up a measuring cylinder of 10Cm3
with a mixture of copper sulphate and distilled water of any one of the
concentrations above.

Table:

Concentration

0.5M

0.4M

0.3M

0.2M

0.1M

0.0M

Volume of water in
cm3

0

2

4

6

8

10

Volume copper
sulphate in cm3

10

8

6

4

2

0

Final volume in cm3

10

10

10

10

10

10

 

Results:

Concentration of copper sulphate
 

Absorbance

0.0 M

0.00

0.1 M

0.31

0.2 M

0.57

0.3 M

0.86

0.4 M

1.13

0.5 M

1.38

 

 

 

 

 

 

 

 

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