organic analysis

Question 1

What is the test and result for an alkene

Answer 1

Shake with Bromine water

Bromine water turns from Orange to Clear and Colourless if alkene present

Question 2

What is the test and result if a haloalkane is present

Answer 2

1. Add NaOH(aq) and warm to substitute the halide ion
2. Acidify with NHO3
3. Add AgNO3
   4.Once a precipitate is formed add dilute ammonia
   5.Then add conc. ammonia

A white, cream or yellow ppt will form of AgCl, AgBr or AgI respectively if a haloalkane was present

On addition of dilute ammonia, any AgCl precipitate will dissolve.

On addition of conc. Ammonia, any AgBr precipitate will dissolve, but any AgI precipitate will remain.

Question 3

What is the test and reagent for a 1 or 2 alcohol

Answer 3

1. Add acidified K2Cr2O7
2. Warm

Solution will turn from Orange to Green if 1⁰ or 2⁰ Alcohol is present.
(Also for aldehyde too)

Question 4

What is the test and the reagent for aldehydes

Answer 4

Warm with Fehling’s Solution
OR
Warm with Tollen’s Solution

Blue solution turns to Brick Red ppt
OR
Silver mirror forms if aldehyde present

Question 5

What is the test and reagent for carboxylic acids

Answer 5

Add Na2CO3 (either solution or solid)

Effervescence (as CO2 is given off)

Question 6

What is the test and result for H2 gas

Answer 6

Apply a lit splint

A squeaky ‘pop’ occurs

Question 7

What is the test and result for CO2 gas

Answer 7

Bubble through lime water

Solution turns cloudy

Question 8

What is the test and result for O2 gas

Answer 8

Apply a glowing splint

The splint will re-light

Question 9

What is the test and result for SO2-4 ions

Answer 9

Add BaCl2 solution

A white ppt will form

Question 10

What is the test and result for Halide ions

Answer 10

White ppt = Cl- ions present which will dissolve in dilute ammonia
Cream ppt = Br- ions present which will only dissolve in conc ammonia
Yellow ppt = I- ions present which is insoluble in ammonia

Question 11

What is the test and result for CO2-3 ions

Answer 11

Add any acid

Effervescence (as CO2 is given off)

Question 12

What is the molecular ion peak

Answer 12

The peak with the largest m/z value

Question 13

Why can’t a mass spectrometer which measures m/z ratios to 1 decimal place tell the difference between C10H16O4 and C11H4O4?

Answer 13

They have the same molecular mass to 1 decimal place

Question 14

Why can’t high resolution mass spectrometry tell the difference between propan-1-ol and propan-2-ol?

Answer 14

They have the same molecular formula, so their molecular mass will be exactly the same.

Question 15

Why does C have a relative molecular mass of 12.00000?

Answer 15

12C is a standard reference

Question 16

Summarise infrared spectroscopy

Answer 16

Bonds absorb infrared radiation that has the same frequency as the vibration of the bond

Question 17

What is the process which occurs inside an IR spectrometer

Answer 17

Infrared radiation shined at the sample
Some frequencies of light absorbed by bonds
Other frequencies are transmitted and detected

Question 18

Which O-H bond is broad , the one in alcohols or carboxylic acids

Answer 18

The one in alcohols

Question 19

Which O-H bond is very broad , the one in alcohols or carboxylic acids

Answer 19

The one in carboxylic acids

Question 20

What is the finger print region

Answer 20

The finger print region is the area of the spectrum 1500cm-1 and below

Question 21

How can mass spectrometry be used to confirm that a compound is definitely ethyl butanoate?

Answer 21

Compare with a known spectrum from a database, it should be an exact match

Question 22

How does the IrR spectra identify purities

Answer 22

The IR spectra of a huge range of PURE samples have been collected and are saved in databases.

If another sample of a compound has been obtained, its IR spectrum can be compared to that of the pure spectrum to indicater if impurities are present.