Chemical tests

Question 1

How do we compare the reactivities of different halogenoalkanes?

Answer 1

-dissolve in ethanol and heat
-add silver nitrate
-measure the time taken for a precipitate to form

Question 2

What are the results of adding silver nitrate to halogenoalkanes and why?

Answer 2

first- containing iodine
last- containing chlorine

(lower down group 7 will be quicker at forming a precipitate because there is decreasing bond enthalpy going down group 7)

white-cream-pale yellow

Question 3

What is Tollen’s reagent?

Answer 3

-the active substance in Tollen’s is [Ag(NH3)2]+
-it is made by mixing silver nitrate and dilute aqueous ammonia

Question 4

What happens when you warm Tollen’s reagent with an aldehyde?

Answer 4

the silver ions are reduced by the aldehyde to silver metal atoms and the aldehyde is oxidised to a carboxylic acid; a silver mirror is produced on the walls of the test tube

Question 5

What happens when you warm Tollen’s reagent with a ketone?

Answer 5

nothing; the solution stays colourless

Question 6

What is Fehling’s solution?

Answer 6

a blue solution containing Cu2+ ions

Question 7

What happens when you warm Fehling’s solution with an aldehyde?

Answer 7

the Cu2+ ions are reduced to Cu+ ions, copper (I) oxide, which is brick red and insoluble, hence producing a red precipitate; the aldehyde is oxidised to a carboxylic acid

Question 8

What happens when you warm Fehling’s solution with a ketone?

Answer 8

nothing; the solution stays blue

Question 9

How to test for hydrogen?

Answer 9

lit wooden splint to a test tube of the gas- if its hydrogen there will be a squeaky pop noise

Question 10

How to test for oxygen?

Answer 10

glowing splint will relight in the presence of oxygen

Question 11

How to test for CO2?

Answer 11

bubble through limewater- it will go cloudy and a white precipitate will form