5A.3 Addition reactions of Alkenes

Question 1

what is stronger a pi bond or a sigma bond and why

Answer 1

since the electrons are held more tightly between the two carbon atoms in a sigma bond, it makes it stronger

Question 2

what is stronger a single bond or a double bond

Answer 2

a double bond but not twice as strong since sigma bonds are stronger than pi bonds

Question 3

what is the test for alkenes

Answer 3

bromine water turns (from orange-brown) to colourless

Question 4

what is the hydrogenation of alkenes

Answer 4

it is a reaction involving adding hydrogen molecule with a NI catalyst at 150c making the alkene and alkane (saturated)

Question 5

what is one use of hydrogenation

Answer 5

the manufacture of margarine from vegetable oil, as vegetable oil is unsaturated and contains a c-c double bond so by the addition of hydrogen the C-C double bond breaks making the compound more saturated (polyunsaturated fats) making it more healthy

Question 6

what is the halogenation of alkenes

Answer 6

it is teh addtion os a halogen itno a alkene to form a dihaloalkane

Question 7

what is the hydration of alkenes

Answer 7

it is when water in steam form is added to an alkene over a phosphoric acid catalyst at 300c and 65 atm to form an alcohol

Question 8

what is the addition of hydrogen halides to an alkene

Answer 8

it is when we add a hydrogen halide (often hydrogen bromide or hydrogen chloride) to form a halogenoalkane

Question 9

the formation of bromoethane cannot be used to test for carbon double bonds, why so

Answer 9

because both the products and reactants are colourless

Question 10

what should we keep in mind is the addition of hydrogen halides to an alkene higher than ethene

Answer 10

where the halide would go it could go on the 1, 2, or 3 carbon

Question 11

what is a diol

Answer 11

a compound containing two OH (alcohol) groups

Question 12

what happens in the oxidation of diol

Answer 12

this is an addition and oxidation reaction where Potassium manganate (VII) and water would be added into an alkene (ethene) at acid condition (by dilute sulfuric acid) where the potassium manganate provides one oxygen atom and the water would provide another oxygen atom and two hydrogen atom forming an alkane-1,2-diol

Question 13

what is the chemical reaction of oxidation of diol

Answer 13

CH2=CH2 + [O] + H2O ——-> CH2OH—CH2OH

Question 14

what happens to the colour of potassium manganate (VII) in the oxidation of diol

Answer 14

it would turn from lilac, purple to colorless giving us another way to distinguish between alkene and alkanes