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LAB_ Standardization of a Sodium Hydroxide Solution by Titration

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					                      Standardization of a Sodium Hydroxide Solution by Titration
PURPOSE: To determine the concentration of an unknown sodium hydroxide solution by acid-base
titration.
INTRODUCTION:
         In this experiment you will determine the concentration of a NaOH solution by acid-base titration.
Finding the concentration is called standardizing a solution. Titration is the name given to the technique
of carefully measuring the volume of a solution required to react with a known amount of another reagent.
A known quantity of a solid acid (potassium hydrogen phthalate) is dissolved in water in a flask, and
phenolphthalein indicator is added. The NaOH solution is added from a buret into the flask containing the
acid. The acid and the base react with one another according to the equation:
                        KHC8H4O4 (aq) + NaOH (aq)  KNaC8H4O4 (aq) + H2O (l)
MATERIALS:
 150 mL beaker                       50 mL graduated cylinder           Phenolphthalein solution
 50 mL buret                         250 mL beaker                      Potassium hydrogen phthalate
 250 mL Erlenmeyer flasks            NaOH solution

PROCEDURE:
  A. Prepare a data table. Record all your experimental results in the table as soon as you obtain them.
  B. Label two Erlenmeyer flasks 1 and 2.
  C. Determine the mass of the vial and the contents. Place about 1.25 g of potassium hydrogen
     phthalate in a flask. Determine the mass of the vial and contents a second time. Between 1.00 g
     and 1.50 g of solid acid should now be in the flask.
  D. Fill the buret so that the meniscus is not above the 10.00 mark, and fasten it to a ring stand with a
     buret clamp.
  E. Read the initial volume of the NaOH solution.
  F. Add 1-3 drops of phenolphthalein indicator.
  G. Place one of the Erlenmeyer flasks under the tip of the buret. A piece of white paper placed under
     the flask will make it easier to see the colour changes.
  H. While continuously swirling the flask to ensure thorough mixing, add NaOH solution from the
     buret.
  I. Read the final volume of the NaOH solution from the buret.
  J. Refill the buret and repeat the titration for a second trial.
  K. A third trial must be preformed if your first two trials vary by more than 5%.
QUESTIONS:
  1. Determine the number of moles of acid used in each titration.
  2. Determine the number of moles of base used in each titration using the number of moles of acid in
     each trial and the equation provided above.
  3. Determine the molar concentration (mol/L) of the NaOH solution obtained from each titration.
     Then average the results.
  4. What is the concentration of a NaOH solution if 32.47 mL of it are required to neutralize 1.27 g of
     potassium hydrogen phthalate?
  5. What is the percentage of potassium hydrogen phthalate in a mixture if 2.81 g of the mixture
     requires 35.61 mL of 0.152 mol/L NaOH to neutralize it?
  6. Potassium hydrogen phthalate is often used in the standardization of basic solutions. Occasionally,
     the purity of this compound when used as a standard acid is slightly greater than 100%. How is
     this possible?
                                           Acid-Base Titration
PURPOSE: To determine the concentration of a solution of hydrochloric acid by acid-base titration.
INTRODUCTION:
In this experiment you will titrate a measured volume of HCl with a solution of NaOH of known
concentration. The acid and the base react with one another according to the equation:
                              HCl (aq) + NaOH (aq)  NaCl (aq) + H2O (l)
MATERIALS:
 50 mL burets                                            standardized solution of NaOH
 10 – 25 mL volumetric pipet                             Phenolphthalein indicator
 250 mL Erlenmeyer flask                                 Unknown solution of HCl

PROCEDURE:
  A. Prepare a data table. Record all your experimental data in the table.
  B. Place a known amount of HCl in a flask.
  C. Fill the buret with NaOH so that the meniscus of the solution is not above the 10.00 mL mark.
  D. Read the initial volume of the NaOH.
  E. Titrate the HCl with the NaOH until the endpoint is reached.
  F. Repeat at least two more times. If your titrations vary by more than 5%, you must repeat that trial.
QUESTIONS:
  1. Determine the number of moles of NaOH used in each titration.
  2. Determine the number of moles of HCl used in each titration.
  3. Determine the concentration of the HCl obtained from each titration. Then average the results.
  4. If 27.31 mL of 0.2115 M NaOH is able to neutralize 37.45 mL of HCl, what is the concentration
     of the acid?
  5. What volume of 0.117 M HCl is needed to neutralize 28.67 mL of 0.137 M KOH?
  6. Why might you be told to use distilled water to wash a drop of solution adhering to one of the
     buret tips into the Erlenmeyer flask?
  7. Would the addition of several millilitres of distilled water to the Erlenmeyer flask during the
     titration affect the results of the titration? Explain your answer.
  8. If 35.93 mL of 0.1590 M NaOH neutralizes 27.48 mL of sulphuric acid, what is the concentration
     of the sulphuric acid?

				
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