Ph And Molarity Lab

Chemistry Lab Report Narendran Sairam pH and Molarity Lab January 9th, 2008

Table Of Contents 1. Objective................................................................................................................................................3 2. Materials.................................................................................................................................................3 3. Experimental Procedure.........................................................................................................................4 4. Obtained Data........................................................................................................................................5 5. Calibration Curve (Day 1).....................................................................................................................6 6. Calibration Curve (Day 2).....................................................................................................................7 7. Calculation of actual pH of samples in accordance with the calibration curve.....................................8 8. Calculation of Molarity of the samples using the pH............................................................................9 9. Calculations concerning NaOH solutions............................................................................................10 10.Calculations concerning HCl Solutions..............................................................................................12 11. Calculation of amount of H3PO4 in coke...........................................................................................15 12.Conclusion..........................................................................................................................................16 13. Appendix A (Calibration Curves).......................................................................................................17

Objective: The objective of this lab is to calculate the pH of 3 standards using a pH meter and the obtained measurements, construct a calibration curve in order to get precise pH measurements of unknown solutions. 

Determine the milliliters of HCl in 1 liter of H2O.



Determine the grams of NaOH dissolved in 1 liter of H2O.

 

Determine the amount of H3PO4 in 12 oz. Of Coke. Determine the amount of NaOH and HCl in 20 ml of H2O

Materials: 

Squirt Bottle



pH Meter



Blue Buffer/Standard (pH = 10)



Red Buffer/Standard (pH = 4.01)



Yellow Buffer/Standard (pH = 7)



Cranergy (Unknown pH)



Fuze(Unknown pH)



Coke (Unknown pH)



Diluted Hcl (Unknown pH)



Diluted NaOH (Unknown pH)

Experimental Procedure:



Get a sample of one of the standards or buffers.



Pour the sample into the beaker, lower the electrode into the beaker and shake it to get the electrons moving. This will enable maximum electron exchange.



Pull out the electrode, wash it using the squirt bottle and repeat the process one more time.



Next, get samples of the other two standards and get their respective pH readings by following the above instructions.



Once the you have the measurements, use them to create a calibration curve. (See appendix A for instructions on how to create a calibration curve.)



Once all the standards have been measured, and the equation of the calibration curve has been obtained, get the samples of Cranergy, Fuze, Coke, diluted HCl and diluted NaOH one at a time.



Measure their respective pH by using the same procedure that was used for the standards.



Make sure to empty out the beaker after measuring a sample and before filling it up to measure the next one.



Once all the solutions with unknown pH are measured, plug their measured values into the equation of the calibration curve in order to obtain their true pH.



Having done this, you will have the pH measurements of all five solutions. This will enable you to calculate their molarity using the formula: Molarity = 10(-pH)



Once you have the molarity of all the samples, you can use data to solve the individual problems about the diluted NaOH and HCl solutions.

Obtained Data: Day 1: 

Buffer 1(Known pH of 7) Room Temperature: 20.3° C Reading 1: 6.9 Reading 2: 7.1



25% Diluted HCl Room Temperature: 20.3° C Reading 1: 0.1 Reading 2: 0.2



Buffer 2(Known pH of 4.01) Room Temperature: 20.3° C Reading 1: 3.9 Reading 2: 4.0



NaOH Solution Room Temperature: 20.3° C Reading 1: 10.48 Reading 2: 10.49



Buffer 3(Known pH of 10) Room Temperature: 20.3° C Reading 1: 9.8 Reading 2: 10.1



Fuze (unknown pH) Room Temperature: 16.2° C Reading 1: 3.68 Reading 2: 3.59



Coke (unknown pH) Room Temperature: 19.5° C Reading 1: 2.70 Reading 2: 2.63



Diluted HCl (unknown pH) Room Temperature: 21.6° C Reading 1: 0.10 Reading 2: 0.09



Diluted NaOH (unknown pH) Room Temperature: 20.1° C Reading 1: 13.57 Reading 2: 13.39

Day 2: 

Buffer 1 (known pH of 7) Room Temperature: 20.0° C Reading 1: 7.03 Reading 2: 7.04



Buffer 2 (known pH of 4.01) Room Temperature: 20.2° C Reading 1: 4.17 Reading 2: 4.23



Buffer 3 (known pH of 10) Room temperature: 19.8° C Reading 1: 10.20 Reading 2: 10.20



Cranergy (unknown pH) Room Temperature: 18.9° C Reading 1: 3.23 Reading 2. 3.18

Note: The readings that are provided here are not guaranteed to be 100% accurate due to the quality of the pH meter. Please keep in mind that there is most probably a small margin of error in all the data that follows because all the other data in this Lab was be obtained from this basic data.

Calibration Curve for Day 1

12

f(x) = 1x + 0.05

10

8

Actual pH

Column B Linear regression for Column B 6

4

2

0 3

4

5

6

7

Measured pH

8

9

10

11

Calibration Curve for Day 2 12

f(x) = 1x - 0.12 10

Actual pH

8

Column B Linear regression for Column B

6

4

2

0 3

4

5

Measured pH 6

7

8

9

10

11

Calculations: The following table shows the actual pH of the measured samples in accordance to the calibration curve. All values in the 'Measured pH' column are arithmetic means of the readings. Day 1 (Actual pH= (Measured pH) + 0.05) Name of sample

Measured pH

Actual pH

Correction

Buffer 1

7

7

None

Buffer 2

3.95

4.01

None

Buffer 3

9.95

10

None

25% diluted HCl

0.15

0.2

0.05

NaOH solution

10.485

10.985

0.05

Day 2 (Actual pH = (Measured pH) – 0.12) Name of sample

Measured pH

Actual pH

Correction

Buffer 1

7.035

7

None

Buffer 2

4.2

4.01

None

Buffer 3

10.2

10

None

Cranergy

3.205

3.073867

0.131133

Fuze

3.635

3.502749

0.13251

Coke

2.665

2.535271

0.129729

Diluted HCl

0.095

-0.02804

0.123047

Diluted NaOH

13.48

13.322152

0.157848

Calculation of Molarity: The following table shows the calculated molarity of the samples using the formula: Molarity = 10(-pH) Day 1 Sample

Actual pH

Molarity

Buffer 1

7

1.0 x 10-7

Buffer 2

4.01

9.77237221 x 10-5

Buffer 3

10

1.0 x 10-10

25% diluted HCl

0.2

6.309573445 x 10-1

NaOH solution

10.985

1.03514219 x 10-11

Sample

Actual pH

Molarity

Buffer 1

7

1.0 x 10-7

Buffer 2

4.01

9.77237221 x 10-5

Buffer 3

10

1.0 x 10-10

Cranergy

3.073867

8.43593063 x 10-4

Fuze

3.502749

3.142324272 x 10-4

Coke

2.535271

2.9156138 x 10-3

Diluted HCl

-0.02804

1.066694363

Diluted NaOH

13.322152

4.76264269 x 10-14

Day 2

Calculation: The following calculation determines the number of grams of NaOH that has dissolved in the given sample. Day 1: (NaOH solution) Known: Molarity = 1.03514219 x 10-11 Number of liters = 1 Unknown: Moles NaOH Grams NaOH Molarity = (moles NaOH)/(liters NaOH) 1.03514219 x 10-11 =(Moles NaOH) / 1 Moles NaOH = 1.03514219 x 10-11 moles Convert from moles to mass: grams NaOH = (moles NaOH) * (grams NaOH) / (1 mole NaOH) grams NaOH = (1.03514219 x 10-11moles NaOH) * (33.9973 grams NaOH) / (1 mole NaOH) grams NaOh = 3.04477764 x 10-13 grams NaOH 3.04477764 x 10-13 grams NaOH were dissolved in the solution on the first day, assuming that the amount of solution was 1 liter. Day 2: (Diluted NaOH solution) Known: Molarity = 4.76264269 x 10-14M Number of liters = 1 Unknown: Moles NaOH

Grams NaOH Molarity = (moles NaOH)/(liters NaOH) 4.76264269 x 10-14 =(Moles NaOH) / 1 Moles NaOH = 4.76264269 x 10-14 moles Convert from moles to mass: grams NaOH = (moles NaOH) * (grams NaOH) / (1 mole NaOH) grams NaOH = (4.76264269 x 10-14 moles NaOH) * (33.9973 grams NaOH) / (1 mole NaOH) grams NaOh = 1.90492848 x 10-12 grams NaOH 1.90492848 x 10-12 grams NaOH were dissolved in the solution on the second day, assuming that the amount of solution was 1 liter. The following calculation shows the amount of NaOH in 20 ml of H2O. Day 1 Molarity = (moles NaOH) / (liters H2O) 1.03514219 x 10-11 M = (moles NaOH) / ( 0.02 liters H2O) moles NaOH = 2.0702858 x 10-13 moles NaOH. Amount of NaOH that would be found in 20 ml of H2O is 2.0702858 x 10-13 moles NaOH. Day 2 Molarity = (moles NaOH) / (liters H2O) 4.76264269 x 10-14 M = (moles NaOH) / ( 0.02 liters H2O) moles NaOH = 9.52528538 x 10-15 moles NaOH. Amount of NaOH that would be found in 20 ml of H2O is 9.52528538 x 10-15 moles NaOH.

Calculation: The following calculation determines the number of milliliters of HCl that were used to create the given solution. Day 1:(25% diluted Hcl) Known: Molarity = 6.309573445 x 10-1 M Number of liters = 1 Liter Density = 1.2g/ml Unknown: Moles HCl Grams HCl Milliliters HCl Molarity = (moles HCl) / (liters HCl) 6.309573445 x 10-1 = (moles HCl) / 1 Moles HCl = 6.309573445 x 10-1 moles Convert from moles to mass: grams HCl = (moles HCl) * (grams HCl) / (1 mole HCl) grams HCl = (6.309573445 x 10-1 moles HCl) * (36.46094 grams HCl) / (1 mole HCl) grams HCl = 23.00529788 grams HCl Density = (grams HCl) / (Millileters HCl) = 1.2g/ml Therefore: 1.2 g/ml= ( 23.00529788 grams HCl) / (Milliliters HCL) Milliliters HCl = 32.41056597 ml HCl The diluted HCl solution contained 19.17108157 milliliters of HCl dissolved in it on the first day, assuming that the amount of solution was 1 liter.

Day 2:(Diluted HCl) Known: Molarity = 1.066694363 M Number of liters = 1 Liter Density = 1.2g/ml Unknown: Moles HCl Grams HCl Milliliters HCl Molarity = (moles HCl) / (liters HCl) 1.066694363 = (moles HCl) / 1 Moles HCl = 1.066694363 moles Convert from moles to mass: grams HCl = (moles HCl) * (grams HCl) / (1 mole HCl) grams HCl = (1.066694363 moles HCl) * (36.46094 grams HCl) / (1 mole HCl) grams HCl = 38.89267917 grams HCl Density = (grams HCl) / (Millileters HCl) = 1.2g/ml Therefore: 1.2 g/ml= (38.89267917 grams HCl) / (Milliliters HCL) Milliliters HCl = 32.41056597 ml HCl

The diluted HCl solution contained 32.41056597 milliliters of HCl dissolved in it on the second day, assuming that the amount of solution was 1 liter.

The following calculation shows the amount of HCl in 20 ml of H2O. Day 1 Molarity = (moles HCl) / (liters H2O) 6.309573445 x 10-1 M = (moles HCl) / ( 0.02 liters H2O) moles HCl = 0.0126191469 moles HCl. Amount of HCl that would be found in 20 ml of H2O is 0.0126191469 moles HCl.. Day 2 Molarity = (moles HCl) / (liters H2O) 1.066694363M = (moles HCl) / ( 0.02 liters H2O) moles HCl = 0.0213338873 moles HCl. Amount of HCl that would be found in 20 ml of H2O is 0.0213338873 moles HCl.

Calculation: This calculations shows the amount of H3PO4 dissolved in 12 fl. oz. (355 ml) of Coke. Molarity = (moles of solute) / (liters of solution) 2.9156138 x 10-3 M = (moles of H3PO4)/(0.355 liters of Coke) moles of H3PO4 = 0.0010350429 moles of H3PO4 Convert from moles to mass: (grams H3PO4) = (moles H3PO4)*(grams H3PO4)/(1 mole H3PO4) grams H3PO4 = 0.1014294636 grams H3PO4 There are 0.1014294636 grams H3PO4 or 0.0010350429 moles of H3PO4 dissolved in 12 fl. oz. Of Coke.

Conclusion: Both the days of this lab involved tedious procedures and judicious following of instructions and, as a result, the lab was a definite success. All the objectives were fulfilled and the results are documented in this report. Unfortunately, owning to the quality of the pH meters and the constantly changing environment of the lab, the pH measurements were not accurate. In fact, the same buffers displayed different results on different days. To solve this dilemma, a calibration curve was used and the equation of this curve is used to calculate the accurate pH of the other samples. With the pH problem solved, the molarity of all the sample was found using the formula : Molarity = 10-pH. Using the molarity the fllowing tasks were accomplished: ●

Finding the number of milliliters of HCl in 1 liter of water.

●

Finding the number of grams of NaOH in 1 liter of water.

●

Finding the amount of NaOH in 20 ml of water.

●

Finding the amount of HCl in 20 ml of water.

●

Finding the amount of H3PO4 in 12 fl. oz. of coke

Appendix A: How to get a calibration curve? Calibrations curves can be obtained by using Microsoft Excel. Follow the instructions below to get your curve: 

Open MicroSoft Excel.



Enter the measured pH values of your standards(the average of the readings if you have more than one reading for each standard.) in column A and the actual pH values of the standards in column B.



Make sure that you have the measured values and the actual values of the standards next to each other on the spread sheet.



Select all the cells and open the Insert menu from Menu Bar and click Chart.



Select you preferences and customize the chart. Make sure to pick a (XY) Scatter Plot to start with.



Once you have the graph, right click on one of the points and select the 'Add treadline' option.



Once the line appears on the graph, right click on the line and select he 'Format treadline' option. A pop up window will show.



Select the Option menu in the pop-up.



Check the box next to the option that says “Display equation of line on the graph.”



Click the Finish button.



Now you will have your calibration curve ready to be used.



You can use the formula of the line to make sure that you have accurate pH measurements of all the samples.