A student prepares a standardized solution of sodium hydroxide by the following
ID: 479587 • Letter: A
Question
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 did the student first prepare a saturated solution?
Unsaturated NaOH solutions are light-sensitive.
Any sodium hydrogen carbonate formed by the reaction of NaOH with atmospheric carbon dioxide will precipitate in the saturated solution.
She can calculate the concentration of the saturated NaOH solution from the Ksp of NaOH.
Saturated solutions are higher in purity than unsaturated solutions.
Explanation / Answer
a)
She prepared in order to have a "blank" solution
Once she is "sure" on what is the actual value of the concentraiton of NAOH, then she can continue with further experiments.
Note that, as stated before, as time passes by, the concentration of NAOH changes since some CaCO3 will precipitate
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