Aliquating Water Droplets 720 Pb PDF

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Aliquoting Water Droplets AIM The aim of Part A was to weigh out aliquots of water using a micropipetting technique with disposable tips. Part B aim was solution preparation of copper sulphate that was in the range of 0.01 – 0.2M and visible absorbance’s was found thus generating a calibration plot in Excel. Part C aim was to calculate the LOD and LOQ using the signal to noise method from five solutions from a stock solution of copper sulphate, the accuracy and precision of this method was compared to Part B. Part C was compared with Part B. A stock solution of 1M was used to prepare solutions using the dilution method. The LOQ and LOD were calculated. The aim of Part D was to calibrate a pH meter, to find the pH of an unknown solution and to neutralise the unknown using titration methods. To quantify the concentration of an analyte in a sample Part E was carried out - for calibration. Three calibration techniques were used and compared: External Calibration Method, Standard Addition Method and Internal Standard Method. Part F (questions) checked for consistency in results using quality control (QC) methods. The aim of Part D was to calibrate a pH meter and to neutralise a waste solution using titration methods. Calibration plots using the External calibration method, the Standard addition method and the Internal standard method to quantify the concentration of an analyte in a sample was the aim of Part E. Part F required the use of control charts to check for consistency in results using quality control methods.

MATERIALS AND METHODS Reagents: Part A: Deionised water. Part B: Copper Sulphate solid. Part C: Copper Sulphate solid. Part D: Unknown Solution B.

Instruments: Part A: Mass balance, weighing boats, thermometer, micropipette and tips.

Part B: Mass balance, weighing boats, volumetric flasks, Varian - Cary 50 UV-Vis Spectrophotometer with Varian Star software, version 2.2, micropipette and tips. Part C: Mass balance, weighing boats, volumetric flasks, Varian - Cary 50 UV-Vis Spectrophotometer with Varian Star software, version 2.2, micropipette and tips. Part D: pH meter and indicator paper.

Procedure: The experiment was carried out in accordance with laboratory manual CS351-A pages 1 to 6 with the following deviation: Part C 0.2M copper sulphate stock solution was used instead of 1M copper sulphate stock solution, the order of the experiment went part B, part C, part D, part A and part F.

DISCUSSION AND CALCULATIONS Part B: Solution Preparation Moles = Mass x Relative Molecular Mass 0.2M – 0.01M = 0.19M 0.19M / 4 = 0.0475M 1: 0.01M 2: 0.01M + 0.0475M = 0.0575M 3: 0.0575M + 0.0475M = 0.105M 4: 0.105M + 0.0475M = 0.1525M 5: 0.1525M + 0.0475M = 0.2M Using the 10ml volumetric flasks the correct amount of copper sulphate (molecular weight = 249.68g/mole) was calculated as follows: 1: 0.01M x 249.68g = 2.49 g / 1000ml x 10ml = 0.0249g 2: 0.0575M x 249.68g = 14.357g / 1000ml x 10 ml = 0.1435g 3: 0.105M x 249.68g = 26.21g / 1000ml x 10ml = 0.2621g 4: 0.1525M x 249.68g = 38.07g / 1000ml x 10ml = 0.3807g 5: 0.2 M x 249.68g = 49.93g / 1000ml x 10 ml = 0.4993g

The absorbance of each reading was recorded in triplicate using the Varian - Cary 50 UV-Vis Spectrophotometer with Varian Star software, version 2.2. The results were tabulated in

Table 1 below. The calculations of the average absorbance, standard deviation and %RSD are present in Table 1 also. Table 1: Absorbance recorded at 795 nm of copper sulphate standards prepared in water (distilled), readings taken at room temperature. Standards

Run 1(1)

Run 2(2)

Run 3(3)

Average

Standard

Concentration

absorbance

Deviation

(M)

(a.u)

%RSD

0.01

0.108

0.162

0.181

0.150

0.037

25.248

0.05

0.556

0.629

0.645

0.610

0.047

7.777

0.10

1.161

1.081

1.055

1.099

0.055

5.026

0.15

1.724

1.702

1.615

1.680

0.057

3.430

0.20

2.166

2.334

1.682

2.060

0.338

16.433

During the Part B experiment there was an error in the calculation which resulted in the calculations having to be altered. The weighing scales that was used was slightly unstable on the table as any weight applied to the table altered the weighing measurements, thus a new weighing scale with more accurate measurements was used. These alterations meant there was slow progress through this part of the experiment resulting in the absorbance reading not being calculated. The absorbance readings from Table 1 are from three different set of results as due to time constraints only one run was done per group. In order to calculate the standard deviation and %RSD three runs must be performed and the results noted. This resulted in the absorbance readings coming from three different samples. This explains the why the %RSD are so high especially for 0.01 M concentration a figure of 25.248% was calculated. This is very high as the %RSD should be as close to 0 as possible. This is because as the different runs have a larger difference in absorbance readings which results in the high %RSD. From taking absorbance results from three different people in the lab resulted in the large difference in absorbance’s between the runs which resulted in the high %RSD. This is because the absorbance reading were taken from different samples that were not prepared by the same person which results in less accurate results. If the %RSD is small or close to 0 this means the data is very precise. The 0.01 M concentration is not as precise due to its large %RSD compared to 0.15 M concentration which has a %RSD of 3.430% which shows that this concentration has the least variation in all the concentrations between the absorbance

readings. In Table 1 the data illustrates an increase in absorbance as the concentration increases. The first run at 0.01 M has an absorbance of 0.108 as the concentration increases to 0.05 M the absorbance also increase to 0.556. The absorbance constantly increases as does the concentration which shows a linearity between concentration and absorbance.

Figure 1: Linear relationship between the Absorbance and the Concentration of the Copper Sulphate Figure 1 illustrates the relationship between the average Absorbance and the Concentration of the Copper Sulphate in the form of a linear calibration curve. The straight line indicates that there is a direct relationship between the average Absorbance and the Concentration of the Copper Sulphate solutions. The R value is 0.9959 which shows how accurate the calibration curve was. Part B: Solution Preparation Table 1:Weighed out Copper Sulphate Solutions: Concentration (M):

Moles in 10ml:

(Concentration/100)

Weight (g):

(Moles in 10ml x Mr of CuH1009S (249.685g/mol)) 0.01

0.0001 0.0245

0.05

0.0005 0.1248

0.10

0.0010 0.2497

0.15

0.0015 0.3745

0.20

0.0020 0.4933

Five solutions of copper sulphate were accurately made up using distilled water in the range 0.010.2M. The data and calculations are seen in Table 1 above. The absorbance of each solution was read three times in the Varian-Cary 50 UV/Visible Spectrophotometer using Varian Star software. The results were tabulated in Table 2 below. The average absorbance, standard deviation and %RSD were calculated and are also shown in Table 2.

Table 2: Absorbances recorded at 795 nm of copper sulphate standards prepared in distilled water, readings taken at room temperature. Standard Concentration (M) Deviation

Run 1 Run 2 Run 3 Average Absorbance (a.u.)

Standard

%RSD

0.01

0.154 0.164 0.150 0.156 0.007 4.62

0.05

0.547 0.564 0.553 0.555 0.009 1.55

0.10

1.108 1.136 1.152 1.132 0.022 1.97

0.15

1.625 1.696 1.702 1.674 0.043 2.56

0.20

2.280 2.280 2.280 2.280 0

0

As seen in the table, as the concentration of the solution increased as did the absorbance. The 0.01M solution had the lowest absorbance readings while the 0.2M solution had the highest. For each solution the three readings were very similar and so an accurate average was obtained. All five solutions contained very small standard deviations which suggested that the absorbance readings were accurate. The %RSD (percentage relative standard deviation) statistically inspects the variation in the data sets.(1) The %RSD states whether the normal standard deviation is a large or small amount compared to the mean for the data set.

Part C: Solution preparation by dilution stock 0.2M stock solution of copper sulphate (molecular weight = 249.69g/mole) was used to prepare five solutions equivalent to Part B. The results from Part B were compared to Part C results. 0.2M x 249.69g = 49.936g / 1000ml = 0.049936 x 50ml = 2.4968g

Five dilutions were made in 10ml volumetric flasks. 1: 0.01M / 1000ml x 10ml = 0.0001M/ml x 5000ml = 0.5ml 2: 0.05M / 1000ml x 10ml = 0.0005M/ml x 5000ml = 2.5ml 3: 0.1M / 1000ml x 10ml = 0.001M/ml x 5000ml = 5ml 4: 0.15M / 1000ml x 10ml = 0.0015M/ml x 5000ml = 7.5ml 5 0.2M / 1000ml x 10ml = 0.002M/ml x 5000ml = 10ml

Table 2: Absorbance recorded at 795 nm of copper sulphate standards prepared in water (distilled), readings taken at room temperature. Standards

Run 3(4)

Average

Standard

Concentration

absorbance

Deviation

(M)

(a.u)

Run 1

Run 2

%RSD

0.01

0.154

0.159

0.162

0.158

0.004

2.552

0.05

0.728

0.714

0.629

0.690

0.053

7.760

0.10

1.121

1.056

1.081

1.086

0.032

3.019

0.15

1.643

1.682

1.702

1.675

0.030

1.790

0.20

2.191

2.245

2.334

2.256

0.072

3.199

Similar to Part B there was alternations that were made to the calculations that meant a 0.2M stock solution of Copper Sulphate had to be prepared instead of a 0.1M stock solution of Copper Sulphate, this again resulted in the slow progress of the experiment in Part C. This resulted in the only two runs of absorbance readings were calculated and because of this the third run of absorbance had to be taken from another lab group in order to form a triplicate of results. The third run was similar to the first two runs which resulted in lower %RSD. When compared to Part B the highest %RSD was 25.248% however in Part C the highest %RSD was 7.760%. The difference was an improvement of 17.488% which show that the data in Part C is more precise than in Part B. This is because two of the runs was done using the same prepared solution in Part C but in Part B due to time restraints the three runs were from different solutions which resulted in the less accurate data. The standard deviation in Part C was closer to 0 than in Part B as this was because the absorbance readings had less of a difference compared to Part B. For Part C the standard deviation for the 0.01 M concentration was 0.004 which showed very little deviation between the runs. In Part C the absorbance

increased as did the concentrations which was similar to Part B which showed a linear relationship between absorption and concentration as one will increase with the other. The data in Part C was more precise than in Part B because the two runs in Part C was used from the same stock solution which lead to the improved accuracy which was indicated by the low %RSD values. The standard concentration of 0.15 M had the lowest %RSD of 1.790% thus was the most accurate data in Part C. In Part B the lowest %RSD was 3.430% which was from the 0.15 M standard concentrate. This figure is nearly double the figure in Part C which illustrates how more accurate the data was in Part C.

Calibration Curve for Copper Sulphate, at 295nm Absorbance at 295nm (a.u)

3 2.5 2 1.5 1

y = 10.786x + 0.0732 R² = 0.9956

0.5 0 0 -0.5

0.05

0.1

0.15

0.2

0.25

Concentration(M)

Figure 2: Linear relationship between the Absorbance and the Concentration of the Copper Sulphate The graph illustrates the direct linear relationship between the Absorbance average and the Concentrations (M) of the Copper Sulphate in a calibration curve. The straight line indicates that there is a direct relationship between the average Absorbance and the Concentration of the Copper Sulphate solutions. The R value is 0.995 which was identical to the calibration curve in Part B which meant the calibration curve was very accurate. The LOD and the LOQ were calculated but they were not obtained by use of the noise method due to time constraints. The LOD was calculated by 3.3 x Standard Deviation of Blank / slope The LOQ was calculated by 3.3 (10 x Standard Deviation of Blank) / slope

Table 3: Data tabulated from Blank Run 1

Run 2

Run 3

Average

Standard

absorbance

Deviation

(a.u) 0.1295

0.131

0.135

0.131

0.002

Slope of curve from Figure 2 = 10.786. LOD = 3.3 x 0.002 / 10.786 = 0.0006119 LOQ = 3.3 (10 x 0.002) / 10.786 = 0.006119

Part A: Micropipette dispensing The measuring of ten different aliquots of water using a micropipette with disposable tips. The water was measured from three different temperatures.

Table 4: Micropipette Measurements at three different temperatures. μl

Cold (4°C),5 weight

Room temperature

Hot (80°C),5 weight

(grams)

(21°C), weight

(grams)

(grams) 100

0.960

0.441

0.991

200

0.961

0.488

0.938

300

0.953

1.348

0.888

400

0.950

0.459

0.903

500

0.947

0.835

0.712

600

0.996

0.889

0.963

700

1.020

0.550

0.973

800

1.005

0.867

0.983

900

1.007

1.190

0.985

1000

0.936

1.239

1.005

Table 5: Average weight, Standard Deviation and %RSD for the three temperatures. Water

Average weight

Standard Deviation

%RDS

Temperature

(grams)

4°C

0.974

0.030

3.123

21°C

0.832

0.342

41.203

80°C

0.934

0.087

9.319

There was a strict time limit during this part of the experiment thus only the room temperature measurements were recorded. The cold temperature and hot temperature measurement results was taken from another person results so the data was all tabulated. As the ul measurements increased so did the weight measurements of the water as this was expected. This show a linear relationship between the quantity of water to the weight of the water at the different temperatures. The % RDS for the room temperature water was 41.203% which was rather high and the reason for this high %RDS was because of human error. The incorrect amount was micro pipetted; this mean there was an increase in the measurement of weight to 1.348 grams at the measurement of 300 ul then at the measurement of 400ul the weight dropped back down to 0.459 grams. This sudden increase in weight was out of proportion as was caused by having the incorrect setting on the micropipette. The lowest %RDs is at 3.123% for the temperature of 4°C which shows that the data collected was very accurate with little errors made and this is quite evident as the standard deviation is 0.030 which is very close to 0 meaning the difference between each measurements was not to great. The %RDS for the 80°C was 9.319% and this is very low which indicates the data for this set of results was also very accurate.

Part E: Calibration Plot Preparation

Calcium Calibration Plot 1.6 1.4

Absorbance (a.u)

1.2 1 0.8

y = 0.1273x + 0.109 R² = 0.9315

0.6 0.4 0.2 0 -0.2

0

2

4

6

8

10

12

Concentration (M)

Figure 3: The linear relationship between Absorbance (a.u) and Concentration (M) of calcium as given in lab manual.

Calculation of Unknown Unknown 1: y = 0.1273x + 0.109 0.26 = 0.1273x + 0.109 x = 1.186M Unknown 2: 1.122 = 0.1273x + 0.109 x = 7.957M Unknown 3: 1.09 = 0.1273x + 0.109 x = 7.7M Unknown 4: 0.759 = 0.1273x + 0.109 x = 5.106M

Standard Addition

Figure 4: The linear relationship between the Nickel Signal and the added Concentration (ml) The graph illustrates the relationship between the Nickel Signal and the added Concentration. The linear region of the calibration curve stops at the x-axis. The equations of the line are y = 0.0186x + 0.3218. Where the x-axis is intercepted by the trend line is the signal from the solution with no added standard.

Internal Standard

Figure 5: The linear relationship between Absorbance (a.u) and Concentration of Pb and Cu.

The calibration curve of the internal standard shows a direct relationship between absorbance and the Concentration of Pb and Cu. The R value was 0.9414 which was close to perfect so it shows the accuracy of the graph. Of all methods the Standard Addition method was the most accurate as it produces a R value of 0.9976 which was the highest value of all the graphs for Part E and this high value indicated the accuracy of the graph and the data.

CONCLUSION Most of the aims that were set out at the start of the experiment were met with great precision. Part B and Part C were easily comparable as both of the techniques produced linear graphs between Absorbance and solution Concentration. However, during part B of the experiment there was some errors with the calculations which in turn slowed down the operation of the experiment and as well as using a weighing scales that was not situated in a correct location to measure accurate results which lead to a lack of results that were produced. So if the experiment was to be repeated again time management would be a very important aspect as it is necessary to have time managed in correct manner so as the fully complete the experiment with all the necessary results obtained. Time planner was necessary to have the experiment completed in time and that was noted to have completed for future experiments. For Part A note all of the experiment was completed on the day of the experiment thus some results were not obtained. Good laboratory skills were necessary to complete that part on time as efficient micro pipetting skills were necessary to comp...