Hydrocarbons

Question 1

Two compounds that have the same molecular formula, but differ in the order in which the atoms are bounded, are called?

Answer 1

Structural isomers

Question 2

1. Alkanes are gases when they have _____ to _____ carbon atoms
2. They are liquids when they have ______ to ______ carbon atoms
3. They are solid when they have _____ to _____ carbon atoms?

Answer 2

1-4 carbon atoms
5-8
9-17

Question 3

Alkanes are soluble in water
True/False

Answer 3

False. Alkanes are insoluble in water i.e they are non-polar
And they have a density of 0.62g/ml - 0.79g/ml)

Question 4

Branching reduces boiling and melting point
True/false

Answer 4

True

Question 5

1. The process by which hydrogen atoms are replaced by halogen atoms, involving free radical production is called?
2. How many reactions are involved in the chain reaction? Name them?

Answer 5

1. Chain reaction
2. 3 ; (a) initiation reaction : lone pair is on the right
   (b) Propagation reaction : lone pair is on both left and right
   (c) Termination reaction : lone pair is at the left

Question 6

Which step of radical chain mechanism requires outside energy?
What can be used as this energy?

Answer 6

1. Initiation reaction
2. UV light is used as the energy

Question 7

1. Why are alkenes more reactive than alkanes?

Answer 7

Because pi bonds are weaker than Sigma bond
OR
Higher energy is needed to break π bond and higher electron density in pi bonds

Question 8

1. Under what condition could ozonolysis of an alkene give only one product?
2. What is used for the test of unsaturation in alkene?
3. Addition of HBr to propene gives two isomeric brominated compounds
   True/False

Answer 8

1. Symmetrical
2. Bromine water. If the reddish brown is disappears then the hydrocarbon is Alkene
3. True

Question 9

The addition of unsymmetrical reagents to unsymmetrical alkenes occur in such away that the negative part of the addendum goes to the carbon atoms of double bond which carries less number of hydrogen atom is called by?

Answer 9

Markovnikoff rule

Question 10

What year was markovnikoff rule formulated?
And by who?

Answer 10

The Russian chemist Vladimir Vasilyevich Markovnikoff in 1865

Question 11

If HCl adds to an unsymmetrical alkene like propene what will the major product be?

Answer 11

2-Chloropropane

Question 12

Hydration of internal alkynes leads to formation?

Answer 12

Ketones

Question 13

Alkenes produces alkanes through what reaction?

Answer 13

Hydrogenation reaction

Question 14

________ and _______ are used to test if an organic compound is saturated or unsaturated

Answer 14

Bromine & kMnO4

Question 15

What are the two ways in which alkenes can be produced?

Answer 15

A. From Halogenation - Elimination
2. Reagent - Alcoholic sodium or potassium hydroxide
3. Conditions - Reflux in alcoholic solution

B. From Alcohols - Dehydration
Reagent: Conc sulphuric acid or conc phosphoric acid
Conditions: Reflux/170°C

Question 16

Ethene is collected over what
And why?

Answer 16

Water
Ethene is collected over water because it has low solubility in water, making it easy to capture and measure.

Question 17

When Ethanol is heated with excess of concentrated sulphuric acid. The gases produced are passed through sodium hydroxide solution why?

Answer 17

To remove the carbon dioxide and sulphur dioxide produced from side reactions

Question 18

1. Alkynes have a length of what?
2. The most important commercial alkyne is?

Answer 18

1. 1.20A°
2. Acetylene which is used as fuel

Question 19

1.The the triple bond is between 2 carbon atoms, the alkyne is_______?

2. If the triple bond is flanked by a hydrogen and carbon, the alkyne is ________,?

Answer 19

Internal
Terminal

Question 20

Terminal alkynes are more stable than internal alkynes
True/False

Answer 20

False
Internal alkynes are more stable than terminal alkynes

N.B: pka of alkane = 50
pka of alkene= 45
pka of alkyne= 25

Question 21

1. When terminal alkynes are deprotonated by very strong bases, what’s the resulting anion called?
2. Deprotonation of terminal alkynes is commonly done with?

Answer 21

1. An Acetylide ion
2. NH2, in the form of NaNH2(sodium amide or sodamide

Question 22

What’s lindlar catalyst used for?

Answer 22

The lindlar catalyst is used to catalyze the hydrogenation of alkynes to alkenes, but not that of alkenes to alkynes

Question 23

What reaction forms cis alkenes and trans alkenes?

Answer 23

The reaction between alkyne and lindlar catalyst gives cis alkenes

The reaction between alkyne and sodium in liquid ammonia gives trans alkenes

Alkyne + lindlar catalyst = Cis alkenes
Alkyne + Sodium in liquid ammonia = transalkenes

Question 24

1. Silver(I) and copper(I) salts reacts with terminal alkynes to form what
2. Why do internal alkynes not react and form a precipitate?

Answer 24

Silver and copper Acetylide

Because they don’t have acidic proton

Question 25

1. Ethyne is prepared by the reaction between what and what? 2. Ethyne is normally prepared by what?

Answer 25

1. Reaction between calcium carbide with water 2. Pyrolysis of methane

Question 26

What are the chemical test that distinguishes between alkenes and alkynes

Answer 26

1. Alkynes react with ammoniacal silver nitrate, and it gives a white ppt whereas alkenes do not 2. Alkynes react with ammoniacal cuprous chloride to form a blue to red colour while alkenes do not

Question 27

Hydration of terminal alkynes yield? Hydration of internal alkynes yield?

Answer 27

Aldehyde Ketones

Question 28

Deprotonation of terminal alkynes is commonly done with? In the form of what?

Answer 28

-NH2 in the form of NaNH2(sodium amide or sodamide)

Question 29

1. When trialkenylborane is treated with alkaline hydrogen peroxide it forms what? 2. What is used to stop hydroboration of terminal alkynes at the first step?

Answer 29

1. An enol. The enol eventually converts into a stable carbonyl product via Reto - enol tautomerism 2. Bulky distributed boranes(R2BH) such as disamyl borane and 9-BBN instead of BH3

Question 30

Ammonical Cuprous chloride on reacting with Ethyne gives what?

Answer 30

Gives copper Acetylide or cuprous and ammonium chloride. The ammonical Cuprous chloride changes from blue to red on reacting with Ethyne. But there's no colour change when it reacts with ethene

Question 31

1. Grignards reagents is also called?

Answer 31

Alkyl magnesium halides

Question 32

1. The reaction

Question 33

Ozonolysis of alkenes give what?

Answer 33

Alcohols, alkanals, ketones, carboxylic acids