Which of these statements about the recrystallisation of an organic solid is correct?
Recrystallisation decreases the purity of the solid
Recrystallisation lowers the melting point of the solid
Recrystallisation decreases the yield of an organic product
Recrystallisation is a chemical process
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The preparation of organic liquids, such as some esters, can involve heating under reflux.
Which statement about heating under reflux is correct?
You can heat organic liquids without evaporation taking place
You can maintain organic liquids at their boiling point for extended periods
Heating is carried out indirectly using a water bath
The apparatus is closed to prevent the escape of materials
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Which of the following can be done with the aid of a separating funnel?
|
|
Neutralise acidic impurities |
Dry organic liquids |
Separate miscible liquids |
|
A |
✔ |
✔ |
✔ |
|
B |
✔ |
✔ |
x |
|
C |
x |
✔ |
✔ |
|
D |
✔ |
x |
x |
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A mixture of ethanol, C2H5OH, ethanoic acid, CH3COOH, ethyl ethanoate, CH3COOCH2CH3, and traces of water remains in a pear-shaped flask after heating under reflux for an hour.
If the mixture is then distilled, what is the order in which the products are likely to be collected in the distillate?
Ethyl ethanoate, ethanol, ethanoic acid
Ethyl ethanoate, ethanoic acid, ethanol
Ethanol, ethyl ethanoate, ethanoic acid
Ethanol, ethanoic acid, ethyl ethanoate
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Which of the following is true about aldehydes and ketones?
Only aldehydes can be identified using Tollens’ reagent
Aldehydes and ketones can be identified using Tollens’ reagent
Aldehydes are positional isomers of ketones
Aldehydes are oxidising agents and ketones are reducing agents
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Which practical technique would be most suitable for purifying a sample of benzoic acid (mp = 122 oC)?
Buchner filtration
Recrystallisation
Using a separating funnel
Simple distillation
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Which of the following is not true about melting point tests?
The melting point tubes must be heated slowly
High melting point organic solids can decompose before melting
The solid must be totally dry and finely powdered
Impurities can lower or raise the melting point of organic solids
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Which of the following reagents can you use to dry a damp sample of ethyl ethanoate?
saturated sodium carbonate solution
anhydrous sodium sulfate
concentrated sulfuric acid
aluminium oxide
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Ibuprofen, paracetamol and aspirin can be identified by which laboratory technique(s)?
|
|
Column chromatography |
TLC |
Melting point test |
|
A |
✓ |
✓ |
✓ |
|
B |
✓ |
✓ |
x |
|
C |
x |
✓ |
✓ |
|
D |
✓ |
x |
x |
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When a Tollen’s test is carried out on propanal, what are the products of the reaction?
CH3CH3COOH + Ag
CH3CH3CH2OH + Ag
CH3CH3COOH + Ag+
CH3CH3CH2OH + Ag+
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A student attempts to purify an organic solid in the following way. The impure organic solid is dissolved in a hot solvent, cooled and allowed to recrystallise and filtered. The residue is washed in fresh solvent and dried.
Which of the following statements is true?
All the impurities have been removed in the process
The impurities remain in the residue
The impurities have a lower melting point that the pure organic solid
A hot filtration is necessary to remove all impurities
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The following apparatus is used in organic chemistry preparations.
Which of the following reactions could be carried out using this apparatus?
C6H4(OH)COOH + CH3COOCOCH3
C6H5COOCH3 + H2SO4/HNO3
CH3CH2OH + Cr2O72- / H+
C6H6 + CH3COOCl
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The following reaction sequence shows an organic synthesis pathway.
Which row correctly shows the reaction conditions of the three steps?
|
|
Step 1 |
Step 2 |
Step 3 |
|
A |
UV light |
Distillation |
Heat under reflux |
|
B |
Room temperature |
Heat under reflux |
Distillation |
|
C |
UV light |
Gentle warming |
Heat under reflux |
|
D |
Room temperature |
Heat under reflux |
Heat under reflux |
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Which of these reactions will make a product that decolourises bromine water and also gives a silver mirror with Tollens’ reagent?
CH3CHCHCH2OH + [O]
CH3CHCHCH2OH + [H]
C6H5CH2OH + [O]
CH3CH2CH2CH2OH + Al2O3
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This question refers to the following reaction scheme:
Which of the following reagents would not bring about the reaction indicated?
Step 1: aqueous NaOH
Step 2: aqueous acidified K2Cr2O7
Step 3: conc NaOH
Step 4: Al2O3
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