EXPERIMENTAL PROCEDURE sadythis section and the Pre-Laboratory Questions before

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EXPERIMENTAL PROCEDURE sadythis section and the Pre-Laboratory Questions before coming to the laboratory Wear safety goggles when performing this experiment.) Sudy this section and the Pre-La Standardization of a Solution of Sodium Hydroxide Doroughly clean, using cleanser and buret brush if necessary, a buret, a graduated inder, a 500-mL Florence flask, and three 250-mL Erlenmeyer flasks so that water will well from them. Fill your wash bottle with distilled water to use at your desk throughout Do this at the sink, not at the distilled-water tap, and do not waste distilled water. this experiment. Rinse the apparatus you have cleaned with distilled water. Prepare a dilute solution of sodium hydroxide by adding about 50. mL of the stock solution ef sodium hydroxide, NaOH, provided on the reagent table, to 250. mL of distilled water contained in a 500-mL Florence flask. Stopper and shake the flask to mix the solution Keep the flask stoppered except when transferring the solution to your buret. Assume the concentration of the NaOH solution you have just prepared is 0.12 M. Using an analytical balance (LABORATORY METHODS C), weigh onto weighing paper three separate samples of about your calculated number of grams of the acid (PRE LABORATORY QUESTION 2). Record your masses in TABLE 17.1A. It is not necessary to weigh exactly the amount calculated, but it is imperative that the mass of each sample be known precisely. After each sample has been weighed, transfer it quantitatively to a lean, clearly labeled 250-mL. Erlenmeyer flask, and add 25 mL of distilled water and two drops of phenolphthalein indicator. You will trate the solution of NaOH you have prepared against each of these solutions of standard acid Set up a ring stand and buret clamp, clean a buret carefully with soap solution, and rinse t thoroughly with distilled water. Practice reading the buret and manipulating the stopcock or pinch clamp (LABORATORY METHODS B) before starting the following uitration. Rinse your buret once with distilled water and than twice with 10-ml portions of the solution of sodium hydroxide you have prepared, draining the solution through the stopcock into a beaker for waste liquid. Fill the buret, using your funnel, nearly to the top of the graduated portion with the solution of sodium hydroxide, making sure that the opxcock and the glass tip are completely flled with the solution. Touch the inner wall of e Sesker to the tip of the buret to remove any hanging drop of solution. Make sure you beaker to the tip o emove your funnel from the top of your buret.

Explanation / Answer

As said let the molarity of NaOH prepared = 0.12 M

moles of H2C2O4. 2H2O = (weight / molecular weight) ; MW= 126.07

each molecule of H2C2O4. 2H2O contains 2 protons ...so moles of protons = 2 X moles of H2C2O4. 2H2O

molarity of H2C2O4. 2H2O = (moles / volume in litres)

Run 1 molarity = (4.22 x 10-3 / 0.025) = 0.169 M

thus using N1V1 = N2V2

0.169 X 25 = 29 X N2

N2 = molarity of NaOH = 0.145

similarly for other runs

N2 = 0.142 M Run 2

N2 = 0.014 M Run 3

1 mole of H+ reacts with 1 mole of OH- ; thus moles of H+ =1 moles of OH-

moles of NaOH = Molarity X volume of NaOH in litres

= 0.144 X 27.7 = 3.99 X 10-3Run 1

similarly for run 2 , moles = 3.63 X 10-3

run 3 =3.24 X 10-3

since trtaric acid has 2 protons

as we know that 1 mol of H+ will react with 1 mol of OH-

thus 2 mol of NaOH will react with 1 mole of tartaric acid; molo of tartaric acid = moles of NaOH / 2

mass of tartaric acid = moles X molecular weight =

Run 1 = 1.99X10-3 X 150 = 0.2985 g

Run 2 = 0.273 g

Run 3 = 0.243 g

thus impurity = sample weight - amount of tartaric acid present

1.31 - 0.2985 = 1.0115 g Run 1

Run 2 = 1.26 - 0.273 = 0.987 g

Run 3 = 1.25 - 0.243 = 1.007

thus % of tartaric acid = (0.2985/1.31) X 100 = 22.8 % Run 1

thus % of impurity = (1.0115/1.31 ) X 100 = 77.2 % Run 1

moles of protons which reacted with OH- ions

thus average impurity % = 100 - average impurity % of tartaric acid =100-21.28 =78.72 %

Run 1 Run 2 Run 3 mass of H2C2O4. 2H2O 0.2622 0.2703 0.2690 moles of H2C2O4. 2H2O 2.11 x 10-3 2.14x 10-3 2.13x 10-3 mole of proton available for OH- 4.22x 10-3 4.28x 10-3 4.26x 10-3 mole of OH- which reacted 4.22x 10-3 4.28 x 10-3 4.26x 10-3 volume of OH- which used 29.0 30.1 29.5 molarity of NaOH solution 0.145 0.142 0.144 average molarity of solution = 0.144

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