Chemistry, Third edition

REVISION QUESTIONS 365

(ii)What technique could you use to separate and collect the

dyes?

19.5.Amino acids, which are colourless and water soluble,

react with a substance called ninhydrin according to the reaction:

amino acid ninhydrinblue/lilac product

(colourless) (colourless)

What technique could you employ to show that urine contains

a mixture of amino acids?

19.6.Whisky contains a number of chemicals that belong to

the alcohol family of organic compounds. If you were given a

bottle of a particular whisky, what technique(s) could you use

to separate and, possibly identify, the constituent alcohols?

19.7.You are a forensic scientist and have been asked to find

out whether the ink from a pen of a suspect could have been

used to write the signature on a forged cheque. How would you

proceed?

19.8.At room temperature, the distribution ratio of butanoic

acid between ethoxyethene (diethyl ether) and water is 3.5. In

an experiment, 150 cm^3 of water containing 0.50 g of butanoic

acid was shaken with 50 cm^3 of ethoxyethane. What mass of

acid did the ethoxyethane extract?

19.9.The following diagram shows the gas chromatogram

obtained when a mixture of heptane and octane was analysed:

(i) Assume the peaks are approximately triangular in shape,

calculate the areas ABC and PQR. The area of a triangle½

base of triangleheight of triangle.

(ii) What can you say about the relative amounts of heptane

and octane in the original mixture?

(iii)Can you think of a method of comparing the area under the

peaks that does not involve calculation and could be used

even if they were not shaped like triangles?

19.10.How would you show that the colours of Smarties are

one single dye, or a mixture of dyes?

0

Signal

strength

Heptane

Octane

AD

B

CP

Time

S

Q

R

DID YOU KNOW?

Electrophoresis involves the separation of charged molecules in an electric field. The molecules move

over paper or through a gel. Negative ions move towards an anode and positive ones towards a cath-

ode. The rate of movement of different ions depends upon their masses and charges.

Protein molecules can be hydrolysed into amino acid fragments and those fragments ionized by using

buffer solutions of a suitable pH. Using electrophoresis on fragments of DNA from body fluids produces

a pattern that is unique to an individual, but certain bands are common in families. DNA fingerprinting

is therefore a valuable tool, both for the forensic scientist and for establishing paternity cases.

Extension material to support this unit is available on our website.