In a certain experiment, the NaOH was added to 25.00 mL of H 2 SO 4 . The volume of NaOH needed to completely react with the H 2 SO 4 will enable the determination of the molarity of H 2 SO 4 . In the same experiment, assume that 12.75 mL of NaOH was needed to completely react with the H2SO4. The molarity of the acid is calculated as follows: Molarity of H 2 SO 4 = 12.75ml ×( 1 L 1000 mL )× 0.200 molNaOH 1 L 1 mol H 2 SO 4 2 mol NaOH ¿ ) ÷ 25 ml 1000 ml = 0.051molarity H 2 SO 4 Equipment / Materials: Phenolphthalein indicator Wash bottle 5×250 mL Erlenmeyer flask 2×burets and clamps wash bottle 500ml bottle with stopper Analytic balance Distilled water 6 M NaOH solution Solid oxalic dihydrate, H 2 SO 4 •2H 2 O Unknown sulfuric acid Experiment Part 1 making standard NaOH solution Date conducted: Nov 9 th , 2017 Preparation: - Obtain 2×50.00-mL burets with clamps, 3×250ml Erlenmeyer flask, and a 500ml bottle from stock room. - Clean and dry all of them. Label them with the relative solution name and waste. Dilution of NaOH solution: - Add 16-17ml 6M NaOH to a 500ml bottle and fill it to the neck with distilled water. - Close the bottle with the stopper and mixed the solution thoroughly by invert the solution gently. - Using M 1 V 1 =M 2 V 2 to find the molarity of the NaOH solution. Prepare the oxalic acid solution: - Weigh the clean and dry Erlenmeyer flask to the nearest 0.0001g on the analytical balance. - Weight a piece of weighing boat to the nearest 0.01g on the top loading balance. - On the piece of weighing boat, weigh 0.3-0.4g H 2 SO 4 •2 H 2 O to the nearest 0.001g and be sure to record your balance readings. - Place the sample in a clean and labeled 250 mL Erlenmeyer flask. - Weight it to the nearest 0.0001g on the analytical balance. - Add distilled water to the Erlenmeyer flask to the 50ml water mark. Make sure to rinse down all the crystal solid that are clinging to the inner surface of the flask. Add 2 drops of the phenolphthalein indicator to the oxalic acid solution. Cleaning the buret:
- Set up a ring stand with a buret clamp and place a clean buret in the buret clamp. Position a magnetic stir plate in such a manner that the buret tip is directly over the center of the stir plate. The stopcock of the buret should be turned perpendicular to the buret. - Place the waste beaker under the buret and close the stopcock. - Deionized or distilled water should be run down the sides of the buret using a wash bottle. Water should flow freely down the inner surface of the buret without forming any droplets over the inner surface. The above process should be repeated two more times. - The buret should be filled with water. The stopcock and the tip need to be cleaned by opening the stopcock and letting water flow through the stopcock and tip into an empty beaker. Make sure there is no air bubble around the stopcock or the tip of the buret. - Re-rinse the buret with 5ml portion of the prepared NaOH solution. Repeat the re-rinsing again. Draining off the solution through the buret tip. Standardization of the NaOH solution: - Fill the buret nearly to the top of the graduated portion with the NaOH solution and make sure that the buret tip is full of solution. Read the initial volume. -
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