The KHP and acid samples must be dried so that their measured masses are actually proportional to the number of moles of each acid sample. If they were not dried, they’d be heavier than they should with the excess water.
What is the role of KHP in titration?
KHP is slightly acidic, and it is often used as a primary standard for acid–base titrations because it is solid and air-stable, making it easy to weigh accurately. … It is also used as a primary standard for calibrating pH meters because, besides the properties just mentioned, its pH in solution is very stable.
What is the role of KHP in the standardization of NaOH?
A commonly used primary standard for titration with sodium hydroxide solution is the weak acid potassium hydrogen phthalate or KHP (C8H5O4K). In this reaction as well, one mole of KHP completely reacts with one mole of NaOH. The titration of NaOH with KHP involves adding NaOH from the burette to a known volume of KHP.
Why does NaOH have to be standardized?
The reason we must standardize strong base solutions is because substances like NaOH will naturally absorb moisture from the air and react with gases in the air, such as CO2, to produce unwanted impurities in the stock sample of the base.
When KHP is added to NaOH what color changes?
Phenolphthalein is colorless in acidic solution, but turns red in basic solution. When one drop more NaOH is added than is required to react with the KHP in a sample, the sample becomes basic and the indicator changes color.
Why is KHP dried before use?
Why is the KHP stored inside the drying oven? Although potassium hydrogen phthalate is an excellent primary standard for titrations, it is somewhat hygroscopic (absorbs water for the atmosphere). So to obtain an accurate mass of the sample, it is necessary to dry the sample before use.
Why KHP is a good primary standard?
Potassium hydrogen phthalate makes for a good primary standard because it is stable, high in purity, non-hydroscopic, highly soluble, non-toxic, high in molecular weight, cheap, and available.
What is the purpose of phenolphthalein?
Phenolphthalein is often used as an indicator in acid–base titrations. For this application, it turns colorless in acidic solutions and pink in basic solutions. It belongs to the class of dyes known as phthalein dyes.
Why is phenolphthalein a good indicator?
Phenolphthalein changes colour at a pH above 7. So it is quite good as an indicator for titrations of strong acids with strong bases. It is also suitable for titrations of weak acids and strong bases, which have an equivalence point at a pH above 7.
Can KHP be a primary standard?
Potassium Hydrogen Phthalate (KHP) is a classic primary standard substance in that it is readily available in high purity