You perform recrystallization of 1 g of impure acetanilide from water. The solub

Question

You perform recrystallization of 1 g of impure acetanilide from water. The solubility of pure acetanilide in hot water is 50g/L The solubility of purea Taking these data into consideration answer the following questions: e in cold water at 0 C is 5g/L What is minimal volume of hot water that is needed to dissolve 1 g of pure acetanilide? Round your answer to nearest integer number Student used 25 ml of hot water to dissolve 1 g of acetanilide. Calculate the minimal amount of acetanilide that will be in the mother liquid at o°c. After measuring the melting point of the recovered acetanilide a student realized that 0.75 g of material still contain water. Student allowed the compound to dry for two more days and obtained the final weight of pure acetanilide as 0.5 g. What was MOLAR percentage c .16 g water in initial sample (0.75g)? Round your answer to the nearest integer. Choose... 18 ml 79% 0.125 g 20 ml 35% 0.02g 62%

Explanation / Answer

In hot water solubility is 50g per litre.This means,

50g can be dissolved completely in water= 1000ml

1g can be dissolved completely in water=(1000÷50)ml=20ml.

So, 20ml of hot water is needed.

Student used 25ml of hot water.If this water is allowed to cool at 0 degree Celsius then it's solubility will decrease.

In cold water solubility is 5g per litre.This means

1000ml of cold water dissolve acetanilide= 5g

25 ml of cold water will dissolve acetanilide=5×25÷1000=.0.125g.

So, 0.125g will be in cold water(mother liquor).

In 0.75 g there was 0.5 g acetanilide,so, there will be 0.75-0.5=0.25 g water.So,

Moles of acetanilide=0.5 g÷ molar mass of acetanilide

=0.5÷135.17=0.0037mol

Similarly, moles of water=0.25÷18=0.0139mol

Total number of moles =0.0037+0.0139=0.0176mol

Now, molar percentage of water

= (mol of water / total moles)×100

=0.0139×100÷0.0176=78.97%=79%

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