A student prepares a standardized solution of sodium hydroxide by the following procedure. The student first prepares a saturated solution of sodium hydroxide using freshly distilled or deionized water. She measures about 5 mL with a graduated cylinder and dilutes to 1 L in a plastic bottle with freshly distilled or deionized water to make a solution that is about 0.1 M. To determine the exact concentration she puts the NaOH solution in a buret and titrates a carefully-weighed pre-dried solid acid of known molar mass. She records the volume of NaOH needed to neutralize it and repeats the process several times to determine the concentration of the NaOH solution. She calculates the concentration and uncertainty in the concentration of the NaOH from the titration data. Why can\'t the student just weigh the sodium hydroxide directly to make a standard? Select all that apply. NaOH pellets react with water. NaOH pellets react with oxygen. NaOH pellets react with hydrogen. NaOH pellets react with carbon dioxide. NaOH pellets react with nitrogen. Why did the student first prepare a saturated solution? A. Saturated solutions are higher in purity than unsaturated solutions. B. Unsaturated NaOH solutions are light-sensitive. C. She can calculate the concentration of the saturated NaOH solution from the Ksp of NaOH. D. Any sodium hydrogen carbonate formed by the reaction of NaOH with atmospheric carbon dioxide will precipitate in the saturated solution. The student prepares the NaOH solution of high purity but unknown concentration by taking about 5 mL of the supernatant at the top of the saturated solution adding it to a plastic bottle with about 1 L of freshly distilled or deionized water. The bottom of the solution contains some white solids which are likely to be (select all correct answers): sodium hydroxide sodium hydrogen sulfate sodium silicate CO2(s) H2O(s) phthalic acid sodium hydrogen carbonate Why is a plastic bottle is generally preferred to glass bottle during the above step? A. The reaction between sodium hydroxide and plastic produces plastic hydroxide. B. Sodium hydroxide renders plastic inert by a process called passivation. C. Sodium hydroxide reacts slowly with glass, forming sodium silicate. D. Sodium hydroxide reacts with polyethylene. The concentration of saturated NaOH is 50.0% w/w and the density is 1.52 g/mL. If exactly 4.00 mL were diluted to 1.000 L, what would be the concentration? Why is potassium acid phthalate (KHC8H4O4, MM = 204.227 g/mol) so widely used as a standard in acid-base titrations? Select all that apply. It is stable to air It is expensive It is easy to dry It has a slowly changing pH at the equivalence point It has a relatively high molar mass It is available in high purity A student dries the pure potassium acid phthalate (KHC8H4O4) in the oven overnight to A. remove water B. purify the matrix C. remove carbon dioxide adn sulfer dioxide D. anneal the crystal structure She weighs 0.1553 g of dry potassium acid phthalate into a flask and adds some water from a graduated cylinder to dissolve it. Why doesn\'t she measure the volume of water with a more accurate device? A. The accuracy of the graduated cylinder is sufficient to measure to two decimal places which is all the precision needed for a titration. B. It would be better to measure the mass because it can be read to four decimal places with an analytical balance. C. The quantity of water actually is important and should be measured accurately because it affects the starting concentration thus the starting pH of the solution. D. The volume of water added is not important because the titration equivalence point depends only on the number of millimoles of potassium acid phthalate and not its concentration. The titration of 0.1553 g of dry potassium acid phthalate (MM = 204.227 g/mol) requires 49.84 mL of NaOH solution. What is the concentration of the NaOH solution? Why is freshly distilled or deionized water used in this standardization? A. Freashly distilled water contains no hydrogen peroxide B. Distilles water contains calcium, which stabilizes the sodium hydroxide C. Freashly deionized water has a pH of 4.72 D. There is little CO2 in freshly deionized or distilled water
