Organic Analysis

Question 1

What is the test and observations/results to differentiate between different haloalkanes (Cl-, Br-, I-)?

Answer 1

1. Add NaOH and warm
2. Acidify with HNO3
3. Add AgNO3

AgCl formed - white ppt
AgBr formed - cream ppt
AgI formed - yellow ppt

4. Add dilute ammonia

AgCl dissolves

5. Add conc ammonia

AgBr dissolves
AgI does not dissolve

Question 2

What is the test for H2 gas?

Answer 2

apply a lit split
squeaky pop occurs

Question 3

What is the test for CO2 gas?

Answer 3

bubble through limewater
solution turns cloudy

Question 4

What is the test for O2 gas?

Answer 4

apply a glowing lit split
split will re-light

Question 5

What is the test for SO42- ions?

Answer 5

add BaCl2 solution
White ppt forms

Question 6

What is the test for halide ions?

Answer 6

1. Add HNO3 then AgNO3
2. Add dilute ammonia
3. Add conc ammonia

white ppt = Cl- ions present which will dissolve in dilute ammonia
cream ppt = Br- ions present which will dissolve in conc ammonia
yellow ppt = I- ions present which is insoluble in ammonia

Question 7

What is the test for CO3^2- ions?

Answer 7

add any acid (e.g. HCl)
effervescence

Question 8

What is the ‘molecular ion’ peak in the mass spectrometer?

Answer 8

the peak with the largest m/z value

Question 9

How do you find the Mr of an unknown molecule in a mass spectrometer

Answer 9

Mr = m/z ratio of the molecular ion peak

Question 10

How do isotopes appear in mass spectrometer?

Answer 10

generates more than one peak in the spectrum

Question 11

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

Answer 11

they have the same molecular mass to 1 dp

Question 12

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

Answer 12

They have the same molecular formula, so their molecular mass will be exactly the same.
Same number of atoms of each element

Question 13

MODEL EQ
Why does C have a relative molecular mass of 12.00000?

Answer 13

12^C is a standard reference

Question 14

What is infrared spectroscopy used to identify?

Answer 14

the FUNCTIONAL GROUPS present in an organic molecule

Question 15

How does infrared spectroscopy work?

Answer 15

infrared energy is absorbed by bonds which makes the bonds vibrate
strong bonds vibrate with very high frequency
weak bonds vibrate with very low frequency

Question 16

what are the peaks on IR spectra called?

Answer 16

absorptions

Question 17

MODEL EQ
what is the fingerprint region?

Answer 17

the area of the spectrum below 1500cm-1

Question 18

MODEL EQ
How can mass spectrometry be used to confirm that a compound is DEFINITELY ethyl butanoate?

Answer 18

compare with a known spectrum from a data base, it should be an exact match