The aim of the experiment is to identify 6 unknown colourless liquids by carrying out different chemical reactions on each of the liquids.
The aim of the experiment is to identify 6 unknown colourless liquids by carrying out different chemical reactions on each of the liquids.
Flow chart showing tests/ reactions to identify the liquids.
a) Bromoethane
b) Butan-1- ol
c) Cyclohexene
d) Ethanoic Acid
e) 2-Methylpropan-2-ol
f) Water
a b c d e f
Forms CO2 gas and a white precipitate when reacting with sodium hydrogen carbonate.
Yes No
d- Ethanoic Acid a b c e f
Decolourises bromine water
Yes No
c- Cyclohexene a b e f
Forms a pale cream precipitate when reacting with silver nitrate solution.
Yes No
a- Bromoethane b e f
Colour change occurs from orange to green when reacting with acidified potassium dichromate (vi)
Yes No
b- Butan-1-ol e f
Turns blue cobalt chloride paper pink
Yes No
f- Water e
Reacts with concentrated Hydrochloric acid, and Chlorine is substituted in place of the OH group. It then reacts with bromine water, decolourising the solution.
Yes
e- 2-Methylpropan-2-ol
Background Information & Methods for Testing:
Haloalkanes:
Bromoethane is a haloalkane. Haloalkanes have the general formula of CnH2n+1X where the X represents the halogen.
Bromoethane is a primary haloalkane. Carbon1 is attached to two hydrogen atoms and one alkyl group, hence a primary haloalkane.
Molecular formula: C2H5Br = CH3CH3Br
Structural formula of Bromoethane:
Carbon
Hydrogen Atoms
Bromine Atom
Alkyl Group
To identify Bromoethane, I will react each of the unidentified liquids with silver nitrate. On reacting, the alkane will form a pale cream precipitate called silver bromide.
In a boiling tube, add 10cm3 of dilute alkali solution in ethanol. Then add 5cm3 of the liquid to the boiling tube and place into a waterbath for 5 minutes. Next, acidify the solution with 1cm3 of nitric acid and then add 1cm3 of silver nitrate solution.
As a result, a pale cream precipitate of silver bromide will be formed. (1)
Equation for the reaction:
AgNO3 + HNO3
C2H5Br C2H5OH + AgBr
Bromoethane Ethanoic Acid Silver Bromide
Alcohols:
Both 2-Methylpropan-2-ol and Butan-1-ol are alcohols. They have the general formula CnH2n+1OH. Alcohols consist of carbon atoms, hydrogen atoms and an OH group.
An example of an alcohol is ethanol, known as alcohol; a drink consumed by people worldwide. Ethanol is produced by fermenting glucose forming two products: Ethanol and Carbon Dioxide:
Equation(1):
...
This is a preview of the whole essay
As a result, a pale cream precipitate of silver bromide will be formed. (1)
Equation for the reaction:
AgNO3 + HNO3
C2H5Br C2H5OH + AgBr
Bromoethane Ethanoic Acid Silver Bromide
Alcohols:
Both 2-Methylpropan-2-ol and Butan-1-ol are alcohols. They have the general formula CnH2n+1OH. Alcohols consist of carbon atoms, hydrogen atoms and an OH group.
An example of an alcohol is ethanol, known as alcohol; a drink consumed by people worldwide. Ethanol is produced by fermenting glucose forming two products: Ethanol and Carbon Dioxide:
Equation(1):
Fermentation
C6H12O6 2C2H5OH + 2CO2
Yeast
Glucose Ethanol Carbon Dioxide
Butan-1-ol has the structure of a Primary Alcohol; Carbon1 has 2 hydrogen atoms, an OH group and one alkyl group attached to it, hence a primary alcohol.
Molecular Formula: C4H9OH = CH3CH2CH2CH2OH
Structural formula of Butan-1-ol:
Carbon1
Hydrogen atoms
OH group
Alkyl group
To identify the primary alcohol, I will react 2cm3 of acidified potassium dichromate (vi) solution with 5cm3 of the unknown liquid in a boiling tube. The mixture will then be heated for 5 minutes in a waterbath. Butan-1-ol will be identified by a colour change. The solution will go from orange to green, therefore proving the liquid to be the primary alcohol. A ketone will be formed too.
Equation for the reaction:
K2CR2O7/H+
CH3CH2CH2CH2OH CH3CH2CH2CHO
Butan-1-ol Heat [-2H] Butanal
2-Methylpropan-2-ol is a Tertiary Alcohol. Carbon2 has no hydrogen atoms, but has 3 alkyl groups and one OH group attached instead.
Molecular Formula: C4H9OH = CH3CCH3OHCH3
Structural formula of 2-Methylpropan-2-ol:
Carbon2
OH group
Alkyl group
To identify the tertiary alcohol, I will react 5cm3 of the liquid with 2cm3 of hydrochloric acid in a boiling tube and leave it at room temperature for 10 minutes. The tertiary alcohol will now have become a haloalkane because chlorine has replaced the OH group. After 10 minutes, I will react each of the liquids with bromine water. The solution that will decolourise will show that the original solution used was the tertiary alcohol, 2-Methylpropan-2-ol. (3)
Equation for the reaction:
HCl (aq)
CH3CCH3OHCH3 CH3CCH3ClCH3 + H2O
2-Methylpropan-2-ol 2-Methyl-chloro-propane Water
Carboxylic Acids:
Ethanoic Acid is a Carboxylic Acid. Carboxylic acids are weak acids, hence only small amounts of its molecules dissociate in water. Carboxylic acids are however, stronger than alcohols due to the weakening of the O-H bond in the acid because of the presence of the carbonyl group and also because of the stability of the anion formed when the H+ ion leaves.
Ethanoic acid consists of an OH group, an alkyl group and a double bond between Carbon2 and oxygen.
Molecular formula: CH3COOH = CH3C=OOH
Structural Formula of Ethanoic Acid:
Carbon2
Double bond between
Carbon2 and Oxygen
OH Group
Alkyl Group
To test for Ethanoic acid, I will react the liquid with some sodium hydrogen carbonate. The carboxylic acid will produce carbon dioxide. This will be detected using limewater which will turn milky white, proving it is a carboxylic acid.
Add 5cm3 of the unknown liquid into a boiling tube. Add a heaped spatula of powdered sodium hydrogen carbonate and place a bung onto the boiling tube. The bung should be attached a tube, one side in the boiling tube, and the other in limewater. If the limewater turns milky white, it will indicate that the original liquid was Ethanoic Acid.
Equation for the reaction:
CH3COOH + NaHCO3 CH3COONa + CO2 + H2O
Ethanoic Acid Sodium Hydrogen Sodium Acetate Carbon Dioxide Water
Carbonate
Alkenes:
Cyclohexene is a type of an Alkene. Alkenes are hydrocarbons which are formed by cracking larger hydrocarbons . Unlike alkanes, alkenes are unsaturated due to the double bond between the carbon atoms. They have the general formula CnH2n. Cyclohexene is a cyclic alkene.. Due to double bonds present in the benzene ring, the general formula for cycloalkanes differs slightly. Cycloalkenes have the following formula: CnH2n-2.
Molecular Formula: C6H10 = CH2CH2CH2CH2CH=CH
Structural Formula of Cyclohexene(4):
Double bond between Carbon atoms
To test for Cyclohexene, I will react it with bromine water. The solution will turn from brown to colourless. This will prove that a double bond is present, therefore the liquid was Cyclohexene. The double bond between the carbon atoms will open up and bromine will be added on forming a haloalkane, 1, 2- dibromohexane.
Add 5cm3 of the unknown liquid into a boiling tube. Then add 1cm3 of Bromine water to the liquid and mix well. If the solution decolourises, it will indicate that the original liquid used was Cyclohexene.(2)
Equation for the reaction:
C6H10 + Br2 C6H10Br2
Cyclohexene Bromine 1, 2-dibromohexane
Water:
Water is a pure substance made up of 2 hydrogen atoms and one oxygen atom. Water makes up 70% of the body and is very important to human life.
Molecular Formula: H2O
Structural Formula of Water:
Oxygen atom.
Hydrogen atoms
To identify water, I will react 10cm3 the unknown substance in a beaker with blue cobalt chloride paper. If the paper turns pink after being in contact with the solution, it will prove the solution is water. The blue colour in the cobalt chloride paper is because of [CoCl4]2- ions. The blue [CoCl4]2- ions convert into [Co(H2O)6]2+ ions, which are pink in colour. (1)
Safety:
Source of hazard
Hazard
Precautions taken
Acidified potassium dichromate (vi)
Breathing in toxic fumes
Conduct tests in a fume cupboard.
Mixing chemicals
Chemical may splash into eyes
Wear safety goggles
Acids
Spillage/ contact with body
Wear gloves and lab coat
Apparatus:
6 boiling tubes
Test tube holder
Water bath
25cm3 beaker
Measuring cylinder
Spatula
Bung
Plastic tubing
Silver nitrate
Dilute alkali solution in ethanol
Nitric acid
Acidified potassium dichromate (VI)
Hydrochloric acid
Bromine water
Sodium hydrogen carbonate (powdered)
Limewater
Blue cobalt chloride paper
Six unidentified liquids- Bromoethane, Butan-1- ol, Cyclohexene, Ethanoic Acid, 2-Methylpropan-2-ol, Water.
Bibliography
) Nelson Thornes- Advanced Chemistry for You- Lawrie Ryan, 2000 Edition
2) CGP AS Level Chemistry- The Revision Guide- 2003 Edition. (page 94)
3) http://en.wikipedia.org/wiki/Tertiary_alcohol#Methanol_and_ethanol
4) http://en.wikipedia.org/wiki/Image:Cyclohexene.png#file
5) http://www.wpbschoolhouse.btinternet.co.uk/page13/page13.htm
Page: As Chemistry
Name: Zoya Khan Candidate No: 0105 Centre No: 13227
