Stoichiometry of reaction in solution

STOICHIOMETRY OF REACTION IN SOLUTION

Stoichiometryof reaction in solution

Reactionsin solution involve acid and bases. The Stoichiometry of acid-basereactions is carried out in laboratories to determine accuratelydetermine the concentration of either a base or acid solution or themolar mass or number of moles of unknown acid or base. Sarker, S. D.,&amp Nahar, L. (2007) describe the process of finding quantitativeinformation on a sample using chemical reaction by reacting a givenvolume of solution (acid or base) of known concentration is referredto as titration. An acid-base titration is used to carry outquantitative analysis of the concentration of an unknown acid of basesolution. When reaction between the solutions has stopped, there arecolor changes. Volumes and known molarity of the compounds involvedare used in the determination of a number of moles involved in thereaction, both for acid and base. This concept can be applied invarious fields and places such as in industries, homes, businesses,research centers, etc. the purpose of this experiment was to studythe reactions of solutions when they are mixed, and find their moleratios.

Materialsand reagents

1.0.07107 M HCl

2.0.1058 M NaOH

3.0.07463 M H2SO4

4.0.06438 M Ba(OH)2

5.Deionized water

6.Phenolphthalein indicator

7.Pipette

8.Burette and stand

9.Beaker

Procedure

Beforestarting the experiment, necessary safety precautions were adhered toas the experiment involved the use of strong acids and bases that maycause chemical burns. Safety goggles were put on. Burette was filledwith 50 ml of NaHO and then clipped. 10 ml of HCl was measured andpoured into a beaker and added 2 drops of phenolphthalein indicator.15ml deionized water was placed under the burette. The originalburette reading was recorded before commencement of titration.Carefully, NaOH was slowly allowed into the beaker while gentlyswirling. When the first color change was noticed, the addition ofNaOH was drop by drop for accuracy and ensures that the solutionturns faint pink. When the color of the solution changed to pink, theend [point of the reaction was reached, and the burette volumerecorded as the final volume. The above procedure was done two timesto attain consistency.

Theabove procedure was repeated but then using sulphuric acid instead ofhydrochloric acid. The measurements were maintained just as in thecase of HCl. Expected volume when the end point is reached was 16 ml.This experiment was followed by replacing NaOH with barium hydroxideand using HCl. 10 ml of HCl was placed in a beaker, and two drops ofphenolphthalein added. 15 ml of deionized water was added to thebeaker and then positioned under the burette for titration. Expectedburette volume was 5-6 ml. Initial burette volume was recorded.Ba(OH)2 added slowly into the beaker until the color of the solutionbegan to turn to faint pink and final volume recorded. This wasrepeated two times. Again, HCl was replaced by sulphuric acid adding10 ml of H2SO4, 15 ml of deionized water and 2 drops ofphenolphthalein placed in a beaker. Expected burette reading was12-13 ml. Barium hydroxide solution was carefully added into thebeaker until the color change was noted and recorded the finalburette reading. This titration was done two more times.

Results

  1. Titration: HCl &amp NaOH

NaOH(aq) + HCl (aq) → NaCl (aq) + H2O(l)

NaOH

HCl

Experimental Ratio NaOH:HCl

Theoretical ratio

NaOH:HCl

Volume (ml)

Moles

Volume (ml)

Moles

0.00689L

0.000729

0.01L

0.00071

1.03 :1

1:1

0.0069 L

0.00073

0.01L

0.00071

1.027:1

1:1

Averageexperimental ratio: 1.0285 : 1

  1. Titration: NaOH +H2SO4

2NaOH(aq) + H2SO4(aq) → Na2SO4(aq) + 2H2O(l)

NaOH

H2SO4

Experimental Ratio NaOH: H2SO4

Theoretical ratio

NaOH: H2SO4

Volume (ml)

Moles

Volume (ml)

Moles

0.0154L

0.00163

0.01L

0.000746

2.18:1

2:1

0.0154L

0.00162

0.01L

0.000746

2.17:1

2:1

Averageexperimental ratio: 2.175:1

  1. Titration: Ba(OH)2 +HCl

Ba(OH)2(aq)+2HCl (aq) → BaCl2(aq) + 2H2O(l)

Ba(OH)2

HCl

Experimental Ratio Ba(OH)2:HCl

Theoretical ratio

Ba(OH)2:HCl

Volume (ml)

Moles

Volume (ml)

Moles

0.00585L

0.000377

.01L

0.00071

0.531:1

1:2

0.0058L

0.000373

.01L

0.00071

0.0525:1

1:2

Averageexperimental ratio: 0.528:1

  1. Titration: Ba(OH)2 +H2SO4

Ba(OH)2(aq) + H2SO4(aq) → BaSO4 (s) + H2O(l)

Ba(OH)2

H2SO4

Experimental Ratio Ba(OH)2: H2SO4

Theoretical ratio

Ba(OH)2: H2SO4

Volume (ml)

Moles

Volume (ml)

Moles

0.013 L

0.000837

.01L

0.00746

1.122:1

1:1

0.013L

0.000837

.01L

0.00746

1.122:1

1:1

Averageexperimental ratio: 1.122:1

Calculations

Numberof moles of HCl used in the experiment:

1000ml contain 0.07107 moles of HCl

10ml contains how many moles?

=0.0007107moles of HCl

Numberof moles of NaOH used in the reaction:

1000ml contains 0.1058 moles of NaOH

10ml will contain how many moles of NaOH?

=0.000729moles NaOH

Theoreticalratio =

1HCl(aq) + 1NaOH (aq) → NaCl (aq) + H2O(l)

Experimentalmole ratio is calculated by dividing the highest moles with thelowest:

Experimentalratio =

1.03:1

Percentageerror =

Titration1:

=2.85%

Titration2:

=8.75%

Titration3:

=47.2 %

Titration4:

=12.20%

Discussion

Themain purpose of this experiment was to study chemical reactionsinvolved in acid-base chemical reactions. When acid and base arereacted, salt and water will be produced. In the first titrationwhere NaOH and HCl were reacted, sodium chloride and water wereproduced as products. In aqueous solution, hydrochloric acid providesthe aqueous hydrogen ion H3O+ (aq) while sodium hydroxide providedaqueous hydroxide ion OH- (aq) (Burton, G. 2000). These two ionsreacted together, H3O+ (aq) acted as the acid while OH- (aq) as abase:

H3O+(aq)+ OH- (aq)→ 2H2O(l)

Asa Bronsted acid, H3O+ donated a proton that was accepted by OH-acting as a Bronsted base. Salt was formed as a result of theformation of an ionic bond between Cl- (aq) and Na+ (aq) to form NaCl(aq) (Clugston, M., &amp Flemming, R. 2000).

Conclusion

Titrationwas used in this experiment to determine the volume of the base thatreacted with the acid. Given the molarity of the acid, the number ofmoles of acid present in the volume (10 ml) used to react with thebased was found. Mole ration for the reaction between the base andacid was employed to find the moles of the base in the burettevolume. The indicator was used to show that the experiment reachedits end point. Faint pink color is the recommended color to show theend point. The difference between the experimental value andtheoretical value may have been due to error during measurement andreading of volume of compound used.

References

Burton,G. (2000).&nbspSaladv chemistry: Pack unit 1.Oxford: Heinemann.

Clugston,M., &amp Flemming, R. (2000).&nbspAdvancedchemistry.Oxford: Univ. Press.

Olmsted,J., &amp Williams, G. M. (1996).&nbspChemistry,the molecular science.St. Louis: Mosby.

Sarker,S. D., &amp Nahar, L. (2007).&nbspChemistryfor pharmacy students: General, organic and natural productchemistry.Chichester, England: John Wiley &amp Sons.