4 Using NaOH as primary standard on the other hand is not suitable because NaOH

4 using naoh as primary standard on the other hand is

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4 Using NaOH as primary standard on the other hand, is not suitable because NaOH is hygroscopic- it absorbs water in the air making it impossible to weigh accurately. 3 At the start of the standardization, solid sodium carbonate was weighed and dissolved with boiled distilled water. Boiled distilled water is used not only in the preparation of this particular solution but also in other base solutions to prevent
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carbonate error. Carbonate error is an error in the determination of endpoint due to carbonic acid formations. This carbonic acid reacts with the base which interrupts the reaction of the analyte base with the acid. Since, some of the base reacts with the carbonic acid, the amount of HCl used to neutralize the base would be less than the actual value which could cause a higher HCl molarity to be calculated. To prevent this, distilled water is first boiled before use to remove the CO 2 that causes carbonate error. After dissolution, 3-4 drops of methyl orange is added to the solution and is then titrated with HCl. Before reaching the endpoint, the solution is boiled first to remove CO 2 . This improves the accuracy of titration because removing CO 2 will change the conditions of the second part of the titration making it a strong base reacting with a strong acid. 4 After boiling, the solution is cooled and then the titration is resumed until the endpoint is reached. Three trials were made for the standardization and the volume of HCl obtained from these trials were used to calculate the molarity of HCl. The net volumes of HCl were precise and are considered to be accurate because the computed average molarity (0.0493 M) is very close to the needed molarity which is 0.050 M. (Table 1) Table 1. Standardization of Hydrochloric Acid Solution Trial 1 2 3 1 o Standard weight, g 0.100 ± 0.001 0.100 ± 0.001 0.102 ± 0.001 Net volume 38.05 38.7 38.6 HCl, ml Molarity HCl, moles/L 0.0495 ± 0.005 0.0487 ± 0.005 0.0498 ± 0.005 After standardization, the soda ash sample was analyzed. A weighed sample was dissolved in boiled distilled water to prevent carbonate error. Then 1-2 drops of phenolphthalein was added to the solution and was titrated to endpoint with HCl. After endpoint, 3-4 drops of methyl orange was
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  • Fall '17
  • Sir Jaden Smith
  • sodium bicarbonate, Sodium hydroxide

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