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Chemistry lab report

By chloetze May 01, 2014 1303 Words
Title : Measuremnt of pH With Indicators
Aim : 1.To investigate concentration of hydrogen ions in hydrochloric acic and colour changes of indicators 2.To determine standard solutions and the unknowns
Variables
Independent variable : Concentration of hydrogen ions in hydrochloric acid.The presence of hydrogen ions is varied by using 5 different concentration of hydrochloric acid of 0.1mol/L,0.01mol/L,0.001mol/L,0.0001mol/L,0.0000mol/L Dependent variable : Colour changes of indicators.The colour change of indicators in unknown 1 and unknown 2 can be observed by comparing with the colour of standard solution which was prepared in Test tube1,Test tube 2,Test tube 3,Test tube 4,Test tube 5 and Test tube 6. Constant variables : 1.The number of drops of indicators which was put in the unknown solutions and standard solutions 2.Volume of water filled in the 50.0ml measuring cylinder 3.Temperature of deionised water

4.Type of indicators used

Procedure
1.Six test tubes having a capacity of greater than 10mL was washed and labelled while the deionised water was being prepared.The test tubes was labelled 1 to 6. 2.5.0 mL of 1.0M HCL was measured into a 50mL measuring cylinder. 3.The 5.0mL HCL solution was diluted to 50.0mL using deionised water.The solution was then transferred to a dry 50.0mL measuring cylinder.The solution was stirred thoroughly using a glass rod. 4.10.0mL of the solution was poured into test tube 1.

5.5.0mL of solution was measured out from the 50.0mL solution prepared in Step 3 and was poured into a 50.0mL measuring cylinder.The solution was then again diluted to 50.0mL using deionised water. 6.10.0mL of the solution was poured into test tube 2.

7.Step 5 was repeated to prepare solution for test tube 3,test tube 4,test tube5 and test tube 6. 8.Test tube 1 to Test tube 3 was added with 2 drops of thymol blue indicator each and was shaken well. 9.Test tube 4 to Test tube 6 was added with 2 drops of methyl orange indicator each and was shaken well. 10.The colour in each test tube was noted and recorded.

11.10.0mL of a unknown 1 solution was poured into two test tube each.The first test tube was added with two drops of thymol blue indicator.The second test tube was added with two drops of methyl orange indicator.Each test tube was shaken well. 12.Step 11 was repeated by using unknown 2 solution.

Results
Test tube number
H+ Concentration
(moles/L)
pH
Indicator
Colour Observed
1
0.10
1.0
Thymol blue
Lilac
2
0.010
2.0
Thymol blue
Pale orange
3
0.0010
3.0
Thymol blue
Pale yellow
4
0.0010
3.0
Methyl orange
Light orange
5
0.00010
4.0
Methyl orange
Yellow
6
0.000010
5.0
Methyl orange
Yellow
Unknown 1
-
1.0
Thymol blue
Lilac
Unknown 1
-
1.0
Methyl orange
Pink
Unknown 2
-
3.0
Thymol blue
Pale yellow
Unknown 2
-
3.0
Methyl orange
Pink

Calculations
The concentration of hydrogen ions (H+) can be calculated as : C1V1=C2V2 C2 = {C1V1} ÷ V2
pH of hydrochloric acid (HCL-) can be calculated as :
-log[H+]
H+ concentration in Test tube 1 : {1.0x 5.0} ÷ 50.0 = 0.10 mol/L pH : -log10[0.10] = 1.0
H+ concentration in Test tube 2 : {0.10 x 5.0} ÷ 50.0 = 0.010 mol/L pH : -log10[0.010] = 2.0
H+ concentration in Test tube 3 and Test tube 4 : {0.010 x 5.0} ÷ 50.0 = 0.0010mol/L pH : -log10[0.0010] = 3.0
H+ concentration in Test tube 5 : {0.0010 x 5.0} ÷ 50.0 = 0.00010mol/L pH : -log10[0.00010] = 4.0

H+ concentration in Test tube 6 : {0.00010 x 5.0} ÷ 50.0 = 0.000010mol//L pH: -log10[0.000010] = 5.0
Discussions
The colour of the thymol blue indicator changed in unknown 1 has the same colour as the thymol blue indicator in test tube 1 which is lilac.The colour of the thymol blue indicator changed in unknown 2 has the same colour as the thymol blue indicator in test tube 3 which is pale yellow.As a result,the pH value of unknown 1 solution is the same as test tube 1 which is pH 1.0 and the pH value of unknown 2 is the same as test tube 3 which is pH 2.0.When the colour of the indicator in two solutions are the same,the pH value of the two solutions will also be the same.The pH value of unknown 1 and unknown 2 can be estimated by comparing it with the colour of standard solutions prepared which is in test tube 1,test tube 2,test tube 3,test tube 4,test tube 5 and test tube 6. Sources of errors

Systematic errors:
1. The eye level is not parallel to the bottom meniscus of the measuring cylinder.This can cause the incorrect reading which will affect the calculation of concentration of hydrogen ions(H+) and pH value of the solutions prepared. 2. The scale of the measuring cylinder used is incorrect.This is will result in the unability to measure the exact volume of the solution. 3. There is only 2 significant figure in the results.This will show low precision. Random errors:

1. The test tube is not cleaned properly.This will lead to dilution of the solution. 2. When the 5.00mL of 1.0mol/L of HCL and distilled wate is poured in the 50.0mL measuring,the solution is not stirred using glass rod.The will result in uneven of the concentration of the solution. 3. Dropper is not used when the bottom meniscus is close to the calibration mark. Improvements

1. Use pipette instead of measuring cylinder.This is because pipette is a more refined measuring instrument which will give a more precise reading. 2. Use another clean measuring cylinder to prepare the next solutions.This will prevent the water from diluting the solution. 3. Stir the solution after pouring the HCL solution and distilled water in the measuring cylinder.This will prevent from uneven concentration of the solution. 4. Make sure that the eye level is parallel to the scale while taking reading.This can prevent from incorrect calculation of concentration and pH. Safety assessment

Hazards :
1. Hydrochloric acid is a corrosive solution.
2. Measuring cylinder,beaker,glass rod,test tubes are fragile. 3. The unknown solutions might be corrosive or irritant.

Precautions:

1. Safety glasses,lab coat and close shoes must be worn during the experiment. 2. Long fringe must be pinned up and hair must be tied.
3. Know the caution while doing the experiment.
4. Glassware must be handled with care.
5. Take the solutions carefully by using beaker.
6. Do not run in the laboratory.
Collaboration
My lab partner was Chudaarleeni Balagopal.Before the experiment,we had a discussion on what we were supposed to do.I was in charged in preparing the unknown solutions while she was in charged to carry out the dilution process.After I had prepared the unknown solutions,I helped Chudaarleeni with her diluting process.There were some misunderstanding while we were performing our experiment,but we sort our problems.I told her that her eye level must be parallel to the bottom meniscus of the measuring cylinder to avoid parallax error.Our teamwork shown has result in a successful experiment. Conclusion

From the results,it can be concluded that the pH value of unknown 1 solution is 1.0 and pH value of unknown 2 solution 3.0.pH value of an unknown solution can be estimated by comparing the solutions with the standard solutions prepared.Unknown 1 solution have the same pH value as test tube 1 because they have the same colour which was lilac in colour.Unknown solution 2 have the sane pH value as test tube 3 because they have the same colour which was pale yellow in colour. Questions:

1.If a solution has a pH of 9.5, is it acidic or basic?
Answer : Basic.
2.Calculate the pH of a 0.0001 M HCI solution. If you had an acetic acid solution of the same concentration, would its pH be higher or lower? Explain. Answer : pH = -log10(0.0001)
= 4.0
The pH of acetic acid is the same as the hydrochloric acid solution(HCL).This is so because the HCL solution and the acetic acid solution have the same concentration of hydrogen ions.(H+)

3.In part A, steps 2 to 5 describe a series of dilutions, beginning with 5.0 mL of 1.0M HCI. Step 6 asks you to calculate the hydrogen ion concentration and pH for each diluted solution. Perform these calculations now and enter the results in the table below. Test Tube

[H+]
pH

Test Tube
[H+]
pH
1
1 x 10-1
1.0

4
1 x 10-3
3.0
2
1 x 10-2
2.0

5
1 x 10-4
4.0
3
1 x 10-3
3.0

6
1 x 10-5
5.0

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