CALIFORNIA STATE UNIVERSITY, LOS ANGELES
Department of Chemistry Chemistry 103 / Section 03- 94356
Prepare and standardize a 0.1 M NaOH solutions
Prepared by: Rodney Pujada
Performance Date: Tuesday, September 29, 2015 Submission Due: Tuesday, October 6, 2015 Professor: Dr. Xin Wen Tuesday and Thursday: 1 pm. – 3:50 p.m.
September 2015
Experiment No 1: Prepare and standardize a 0.1 M NaOH solutions I.
II.
PURPOSE Performing this lab successfully will allow us to learn an important lab technique called titration. Titration is the technique to find the concentration of unknown solution by the formula Ma x Va = Mb x Vb to determine the exact concentration of sodium hydroxide solution. PRINCIPLES Titration is a laboratory technique that can be used to determine the concentration of certain solutions by chemical reaction. A standard solution of known concentration is “titrated against” (reacted with) a solution of unknown concentration. An indicator can signal the completion of the reaction (by color change) and the concentration of the unknown solution can be determined. Any chemicals that react in solution can be titrated with each other. Since acids and bases are usually found in solution, they are commonly involved in titrations. Titrations involving a strong acid or a strong base involve the neutralization reaction between hydrogen ions (or hydronium) and hydroxide ions. These ions combine to form the neutral water molecule: H+ + OH- ---> H2O or H3O + + OH- ---> 2 H2O An indicator is any substance in solution that changes its color as it reacts with either an acid or a base. Selecting the proper indicator is important because each indicator changes its color over a particular range of pH values.
This experiment use titrimetric analysis to determine the concentration of unknown sample. It involves preparation of a solution that has the approximate concentration desired (NaOH), determination of the concentration by direct titration against a primary standard, and a test of the accuracy of your determined concentration by comparison with a known standard. After the NaOH standarzided, we can calculate the concentration of the sample by the principle of relation of moles that react with the unknown acid, and calculate its molarity, using: Moles solute before dilution = moles solute after dilution
……………………………. Formula No1 III.
EXPERIMENTAL PROCEDURES
3.1 Material 20-mL graduated cylinder,50 mL Buret, three 250 mL Erlenmeyer flask, buret clamp, wash bottle, 1L plastic bottle, funnel, 50 mL and 500 mL beaker, phenolphthalein NaOH (known concentration), distilled water, 3M NaOH concentrated, and sulfanic acid standard solution (known concentration).
3.2
Procedure
3.2.1 Preparation of 1 M Sodium Hydroxide Solution solution. a. Measure 16.7 mL of 3M NaOH with 20mL graduated cylinder. b. Add small amount of water and pour it into a volumetric flask of 250 mL. c. Fill the volumetric flask until the mark of 250 mL. d. Pour this volume into a 1 liter plastic bottle. e. Fill the volumetric flask with distilled water to get 500 mL into the plastic bottle. 3.2.2 Calculate the Molarity of Sodium Hydroxide Solution by titration a) Clean and rinse the buret with distilled water. b) Precondition the buret by rinsing it with the NaOH solution two or three times, and fill the buret with a funnel. c) Fill the buret with NaOH to exact measurement. d) Remove all gas bubbles in the liquid column of the buret and attach a buret clamp. e) Read the initial volume of NaOH by recording the position of mark that line up with the meniscus of the liquid column. f) Prepare three Erlenmeyers. g) Take 25 mL of sulfamic acid standard with known concentration into three erlemeyers. h) Add four drops of indicator (phenolphthalein) into the Erlenmeyer flask of sulfamic acid standard. i) Place the Erlenmeyer flask under the buret; open the stopcock slowly to add the NaOH solution. The end-point is near when the solution changes the color pink. At this point, open the stopcock slowly, adding drop by drop. j) Record the final volume Vf NaOH when the solution turn to pink. IV Data and Calculation
Titration Data
Run 1
Run 2
Run 3
Molaridad of sulfamic acid standard (M) Initial buret reading Vi NaOH (mL) Final buret reading Vf NaOH(mL)
0.104 +0.47%
0.104 +0.47%
0.104 +0.47%
0.0
0.0
0.0
28.6
28.0
28.6
Volume of NaOH used (mL)
28.6
28.0
28.6
4.1
Calculate the amount of 0.1 M NaOH by dilution of 3M NaOH
Calculate the amount of 0.1 M NaOH by dilute 3 M of NaOH, using following the formula…..
the
……………………………. Formula No1
Data: M1 = 3 M of NaOH known. V1 = ?? M2 = 0.1 M of NaOH that we expected. V2 = 500 mL of NaOH that we expected. Using the formula No1 to calculate V1 =? Evalute V1: V1 = ( M2* V2) / M1 Replace the data V1 = ( 0.1 M *500 mL) / (3M) V1 = volume of NaOH diluted= 16.7 mL 4.2
Standardization of the 0.1M NaOH solution. ……………………………. Formula No1
DATA for Run 1 M1 = 0.104 M of sulfamic acid standard V1 = 25 mL of sulfamic acid standard M2 = ??? of NaOH that we expected in the plastic bottle. V2 = 500 mL of NaOH that we expected in the plastic bottle. Using the formula No 1 to evaluate M1 =? M2 = ( M1* V1) / V2 Replace the data M2 = ( 0.104 M * 25mL) / (28.6) M2 = 0.091 M of NaOH in the plastic bottle
Titration Data
Run 1
Run 2
Run 3
Molaridad of sulfamic acid standard (M) Initial buret reading Vi NaOH (mL) Final buret reading Vf NaOH(mL)
0.104 +0.47%
0.104 +0.47%
0.104 +0.47%
0.0
0.0
0.0
28.6
28.0
28.6
Volume of NaOH used (mL)
28.6
28.0
28.6
Molarity NaOH bottle (M)
0.091
0.093
0.091
4.3
Calculate the percent error % Percent error = ( Vpractical — Vtheoric) x 100 % ………………. Formula No 2 V theoric
Data: Molarity NaOH (approx) = V prac = 0.1 M Molarity NaOH (standard) = V teoric = 0.087 M Using the formula No 2 to evaluate percent of error.
Percent error = (0.091 - 0.1) x 100 % = -9 % 0.1 Percent error = -9 % V Results and Discussion
Titration Data of 0.1 M
Run 1
Run 2
Run 3
Molarity NaOH bottle (M)
0.091
0.093
0.091
NaOH
Molarity NaOH bottle Average (M)
0.092
In this lab we calculate the concentration of our NaOH diluted solution is 0.092 M . By definition one equivalent (or equivalent weight) of a substance is the amount of that substance which supplies or consumes one mol of reactive species. In acid-base chemistry the reactive species is the hydrogen ion (H1+) while in oxidation-reduction chemistry the reactive species is the electron. We recommended follow the correct procedure and use Erlenmeyer flask for the titration that are appropriate material. Also, we must follow the correct technique of titration because these factor alter the end point of the titration. Using the titration technique correctly is important. A right handed person should titrate with the left hand, swirling the flask with the right hand and agitate strongly to avoid to past the end point of the titration as occurring in our run1 and run3.
VI Conclusions
We conclude that the concentration of sodium hydroxide is 0.092 M. Our percent of error is consequence to measuring 16.7 mL of 3M NaOH with 20mL graduated cylinder instead to use a volumetric pipet or buret with 3M NaOH solution. If we believe that run #2 should be omitted because we know that we accidentally overshot the equivalence point and our titration flask was little bright pink; we can report 0.093 M NaOH with less percent of error.
VII References D.C. Harris, Quantitative Chemical Analysis (7th ed., W. H. Freeman, NY, 2007) pp. 121-124, 221–218, Skoog, D. A.; West, D. M. Fundamentals of Analytical Chemistry; Holt, Rinehart and Winston: New York, 1963; pp 341-351. Sweeder, R. D.; Jeffery, K. A.; A comprehensive general chemistry demonstration. J. Chem. Ed., 2013, 90, 96-98. doi:10.1021/ed300367y
