Lab 2

Question 1

How to determine an unidentified carboxylic acid?(first 3 step)

Answer 1

1. Weigh 0.15g of the acid and transfer it to 125 ml Erlenmeyer flask. Add 10m ml of methanol and 2 drops of phenolphthalein indicator and swirl the contents to ensure proper mixing
2. Titrate against a standardized 0.1M NaOH solution. The change in color from colorless to pink can be noted once the equivalence point has been reached. Record your readings
3. Repeat the titration with a new weighted sample of the carboxylic acid. The mass used for the second titration should be different from the mass used for the first determination

Question 2

How to determine an unidentified carboxylic acid? (Last 2 steps)

Answer 2

4. After the mass of the second titration is obtained, calculate the molar mass, the two values agree within +-2 amu. If they do not, perform a third titration
5. Wash the biurette after the last titration, while still clamped. Drain the biurette, then slowly add about 10 mls of dilute a HCl and drain; finally add 50 ml of distilled water and drain
6. Identify your unknown carboxylic acid by matching your result with the possibilities listed in the table provided

Question 3

What are the purpose of boiling chips?

Answer 3

Added to liquids to make them boil more calmly, often used in distillation for heating

They provide nucleation sites so the liquid boils smoothly

Question 4

Explain the principle behind the procedure for identifying an unidentified cboxylic acid

Answer 4

At the equivalence point of a titration, the moles of the base and acid are equivalent. The moles of the OH, are added to the biurette are calculated from the base.

Because it is a mono protein acid, the moles of acid are equal to the moles of OH at the end point of titration

Question 5

What are the first 3 steps of the procedure of caffeine extraction

Answer 5

1. In a 400 mL beaker, place 10 tea bags and approximately 100 mL of water . Boil it for 15 mins
2. Remove the beaker from the hot plate, remove and discard the teabags, and dissolve 15g of Na2CO3 in the solution by stirring
3. Cool the tea solution in and ice water bath, then transfer it to a separators funnel

Question 6

What are steps (4-6) of caffeine extraction?

Answer 6

4. Add 20 mL of methylene chloride via a funnel and shake the mixture gently. DO not shake to vigorously, or you will get an emulsion (I.e. a mixture consisting of droplets of one phase suspended into the other). If this happen let it stand for about 15 minutes to allow separation of the layers
5. Extract the aqueous layer with another 20mL portion of methylene chloride
6. Combine the organic extracts in a 125mL conical flask, and dry them with about 1g of anhydrous MgSO4

Question 7

What are steps (7-10) for caffeine extraction?

Answer 7

7. Allow the solution to stand for about 10 minutes, swirling it occasionally to complete the drying
8. Keep the aqueous phase in a beaker- do not discard until you are sure you do not need anymore
9. Gravity filter the methylene chloride solution into a small pre-weighed beaker. Add one boiling chip, and carefully evaporate the solvent to dryness in a hot water bath or a large beaker of water on a hot plate in the hood
10. Remove the boiling chip, reweigh the beaker, and calculate the yield of crude caffeine

Question 8

Give the procedure to perform the titration of an amino acid (glycine)

Answer 8

Pipette 25 cm^3 of glycine into the conical flask provided and measure the pH. Now fill the burette to the zero mark with. 0.1M NaOH.

Using the burette, add 5mL of 0.1M NaOH to 25cm^3 of glycine and record the pH of the resulting solution

Continue adding 5 ml of NaOH at a time and measure the pH for every 5 ml added. Record your results as shown in the table below

Question 9

Explain the theory behind the titration of an amino acid(first part)

Answer 9

Titration curves are obtained when the pH of a given volume of a sample solution varies after successive addition of acid or alkali. Curves usually are plot of pH versus the volume of the titration added

Amino acids are amphoteric molecules which can be titrated against acids of alkali. Polyprotic acids which exist as zwitter at neutral pH. When an aqueous solution of an amino acid is titrated with an acid, it acts as a base, with a base, it acts as an acid

Question 10

Explain the theory behind the titration of an amino acid ( second part)

Answer 10

In this experiment we are finding out the titration curve the amino acid Glycine.

Glycine is a diprotic amino acid which means that it has 2 dissociable protons, one on the alpha amino group and the other on the carboxyl group. In this fully protonsted form; it can donate two protons during its complete titration with a base. In the case of glycine, the R group does not contribute a dissociable proton

The dissociation of proton proceeds in a certain order which depends on the acidity of the proton: the one which is most acidic and having a lower pKa will dissociate first. So, the proton on the alpha COOH group(pKa1) will dissociate before that on the alpha NH3 group(pKa2)

Question 11

Explain the theory of extraction of caffeine part 1/3

Answer 11

Extraction with a solvent is a separation technique most frequently employed to isolate one or more components of a mixture. The technique is based on the preferential solubilities of the components of the mixture for two different immiscible solvents

It involves the partial removal of a solute from one liquid in which it is less soluble to another immiscible liquid in which it is more soluble. In most cases, an organic solvent is used to remove an organic solute from an aqueous solution or suspension. If a solute is shaken with a mixture of two immiscible solvents at a fixed temperature, the solute will distribute itself in both solvents according to its solubility in each.

Question 12

A hindsberg test is administered to an amine which dissolves in basic solution. What type of a,one is this?

Answer 12

Primary amine

Question 13

A hinsberg test was treated with an amine and the solution was insoluble in basic solution. Why and what type of amine is this?

Answer 13

Secondary amine produce sulfonamides that are insoluble in basic solution

Question 14

An Amine was treated with hinsberg test and doesn’t react. What type of amine is this?

Answer 14

Tertiary amines fail to react with benzene sulfonyl chloride

Question 15

How can primary aliphatic amines and primary aromatic amines be distinguished ?

Answer 15

Primary aromatic amines, have the ability to undergo diazotization and coupling with phenol to form a dye under the hinsberg test.

Unlike primary aromatic amines

Question 16

An amine undergoes a nitrous acid test and forms a diazonium salt. What type of amine is this and why?

Answer 16

Primary amines form diazonium salt which is unstable and loses nitrogen gas which bubbles out of solution

Question 17

An amine is given an the nitrous acid test and the solution separates from an aqueous solution that is yellow or orange liquid. No N2 bubbles form. What type of amine is this and why?

Answer 17

Secondary amines, form an N-nitroso compound which is relatively stable and separates from aqueous solution as a yellow or orange liquid.

N2 gas is not evolved

Question 18

An amine undergoes a nitrous acid test, and doesn’t react, what type of amine is it and why

Answer 18

Tertiary amines do not react in nitrous acid test