June 2009 Chemistry Regents #77-78

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Questions

Base your answers to questions 77 through 78 on the information below. In performing a titration, a student adds three drops of phenolphthalein to a flask containing 25.00 milliliters of HCl(aq). Using a buret, the student slowly adds 0.150 M NaOH(aq) to the flask until one drop causes the indicator to turn light pink. The student determines that a total volume of 20.20 milliliters of NaOH(aq) was used in this titration. 77 The concentration of the NaOH(aq) used in the titration is expressed to what number of significant figures? [1] HIGHLIGHT TO SEE THE ANSWER 3Sig. Figs. based on 0.150M 78 Calculate the molarity of the HCl(aq) used in this titration. Your response must include both a correct numerical setup and the calculated result. [2] HIGHLIGHT TO SEE THE ANSWER Allow 1 credit for    (MA)(25.00 mL) = (0.150 M)(20.20 mL) Allow 1 credit for 0.121 M Next Questions

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