In a titration experiment , 25 .0cm^3 of sodium hydroxide is titrated against a standard solution of hydrochloric acidic with phenolphthalein as indicator .Which of the following statements concerning this experiment is / are correct?
1)The colour of phenolphthalein changes from pink to colourless at the end point.
2))The colour of phenolphthalein changes from colourless to pink at the end point.
3) A pipette is used to measure the volume of the hydrochloric acid.
Chemistry....____ Explain it
2007-02-19 7:20 pm
回答 (2)
2007-02-19 7:30 pm
✔ 最佳答案
When a fixed volume of NaOH is titrated against HCl, the hydrochloric acid is put in the burette and added onto the flask containing NaOH.Since at the beginning, there is excess of NaOH, the colour of phenolphthalein is pink (alkaline), and gradually as excess acid is added, it will become colourless.
The answer is therefore:
1)The colour of phenolphthalein changes from pink to colourless at the end point.
2007-02-19 7:25 pm
2))The colour of phenolphthalein changes from colourless to pink at the end point
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