DISCUSSION

1. Standardization of HCl with borax (Na2B4O7.10H2O)

HCl is not a primary standard solution, therefore, standardization is necessary by using borax (Na2 B4O 7.10H2O). Were using theacid-base titration method. Titration is in an experiment using 1.91 grams of Na2B4O7.10H 2 O in 100 ml of aquades with a relative molecular mass 382 g/mol. Reacting Na2B4O7.10H2O are already in the set volume of 10 ml with indicators MO.Do the titrationby using a standardized HCl. Drops HCl little by little to erlemeyer that contains Na2B4O7.10H2O until the color changes 2 times or titration is stopped at the secondpoint of the equivalent.

Based on the theory, we know that the endpoint of titration is almost equal to the equivalent point. The formula: V1. N1 = V2. N2. So put the formula to calculate standardized HCl with Na2B4O7.10H2O 0.1 N,standardized HCl concentration is obtained by 0.0938 N.

2. Standardization of NaOH with Oxalic Acid (H2C2O4)

H2C2O4 that we used when titration with NaOH is the primary standard of known molarity and volume. In our experiments this time were using 7.8815 grams of H2C2O4in 1250 ml of aquadeswith a relative molecular mass 126.07 g/mol. Reacting PP indicator with 10 ml NaOH, theres no any color change (keep clear). Use a standardized NaOH, then do the titration. Drops little by little NaOH to erlenmeyer that contains H2C2O4 until the color changes 2 timesor titration is stopped at the second point of the equivalent. The reason is endpoint of the first titration just take the H+ ions for each molecule of carbonate, while the endpoint of the second titration needed 2H+ ions, because NaOH that we mix with H2C2O4 makes the color of the mixture solution change becomes mauve. The reaction is :

C2H2O 4.2H 2O + NaOH => NaCHO4 + CO2 + H2O

So put titration calculation formula V1. N1 = V2. N2, that calculatestandardized NaOH with H2C2O4 0.1N, so standardized HCl concentration is obtained by 0.094 N.

CONCLUSSION

HCl solution can be standardized using borax (Na2B4O7.10H2O) with indicator MO (Methyl Orange), while the NaOH can be standardized using oxalic acid (H2C2O4) with PP indicator (Phenolphthalein). Standardization was performed using acid-base titration method, standardization is important for the substance to be standardized and will be used to analysis a substance. The purpose of standardization itself is to determine concentration of a solution with real-true value. The practical results showed 0.0938 Nfor thestandardized HCl concentration, and 0.094 N for the standardized NaOH concentration.

DASAR TEORI BAGIAN OKTA

There are two methods to standardize the solution:

1. Making a direct solution by dissolving a pure substance with a specific weight, then diluted to obtain a certain volume appropriately. This solution is the primary standard solution. Substances used for the primary standard solution must comply the following conditions :

a. Easily obtained in pure form or in a condition that is known purity. contaminant does not exceed 0.01-0.02%

b. must be stable

c. This substance easily dried, not hygroscopic so it cant absorb water and also not absorb CO2 during the development (sukmariah, 1990)

2. solution concentration solution concentration cant be known by weighing the substance then dissolving it to obtain a certain volume, but it can be standardized with primary standard solution, is a secondary standard solution. Condition of a substance to be a secondary standard solution is :

a. Not easily obtained in pure form or in a condition that is known purity

b. This substance not easily dried, hygroscopic, absorb water and also absorb CO2 during the development

c. Purity level is lower than the primary standard solution

d. Have a high equivalent weight to minimize weighing errors

Substances which can made as a primary standard solution is oxalic acid, borax, benzoic acid (C6H5COOH), K2Cr2O7, As2O3 and NaCl.