Question

pl#3

QUESTION 1

1. A mixture of 0.810g of BaCl ₂^.2H ₂O and Na ₂SO ₄ produces 0.466g of BaSO ₄, the limiting reactant in the reaction is Na ₂SO ₄. Calculate the percent of BaCl ₂^.2H ₂O and Na ₂SO ₄ in the original mixture.

QUESTION 2

1. Because of the finely divided nature of the Ba ₃(PO ₄) ₂ precipitate, some of it passes through the filter and is not collected. How does this loss of precipitate affect the reported percentage of the limiting reactant in the salt mixture?

QUESTION 3

1. What does the expression, "digesting a precipitate" mean?

QUESTION 4

1. When 0.629g of Na ₃PO ₄^.12H ₂O )molar mass =380.12g/mol) and 0.527g BaCl _2.^.2H ₂O (molar mass=244.30g/mol) are mixed with water forming 500ml of solution, how many grams of Ba ₃(PO ₄) ₂ (molar mass =601.96g/mol) precipitates?

PL#4

QUESTION 1

1. A 0.429 g sample of KHC ₈H ₄O ₄ (molar mass =204.44g/mol) requires 23 ml of a NaOH solution to reach the phenolphthalein endpoint. Calculate the molar concentration of the NaOH solution.

QUESTION 2

1. A concentrated NaOH solution is diluted with previously boiled, deionized water to remove traces of CO ₂. How do traces of CO ₂ affect the concentration of NaOH in solution?

QUESTION 3

1. Drops of titrant cling to the wall of a dirty buret. If a dirty buret is used for stardardizing a NaOH solution (the NaOH solution is the titrant) against solid KHC ₈H ₄O ₄, is the reported molar mass concentration of the NaOH high or low?

QUESTION 4

1. " If 2 drops are good, 20drops must be better!" Explain why this reasoning is not logical when adding phenolphthalein indicator for an endpoint determination.

QUESTION 5

1. Pure potassium hydrogen phthalate(KHP) is used for stardardization of the sodium hydroxide solution. Suppose that the KHP is not completely dry. Will the reported molar concentration of NaOH solution be too high, too low, or unaffected because of the moistness of the KHP? Explain.

QUESTION 6

1. The mass of KHC ₈H ₄O ₄ is measured to the nearest milligram; however, the volume of water in which it is dissolved is never of concern-water is even added to the wall of the Erlenmeyer flask during the titration. Explain why water added to the KHP has no effect on the data, whereas water added to the NaOH solution may drastically affect the data.

Answer 1

#3

Digestion of precipitate means that dissolution of precipitate. When precipitate in a solution dissove completely and give a clear solution then we can say that the precipitate is digested. It may occur some external factor like temperature and adding some chemical species.

#4

If 2 drops are good then 20 drops will be better is chemically wrong statement. Actually phenolphthalein has its own pH working range and dissociation when we add 20 drops of it it will affect the resulting pH of the solution or mixture by forming HIn compound and the end point will be affected at par. So excess addition will cause wrong end point of titration.