OCR A-Level Chemistry ULTIMATE PAG SET
exam with verified solutions
What is needed to carry out "heating under reflux"? - correct answer
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✔Equipment: Vertical condenser (clamps etc), Pear-shaped flask, antibumping
| | | | | | | |
granules, grease/vaseline and a heat source
| | | | | |
*Antibumping granules*-used to make the liquid boil calmly and prevent
| | | | | | | | |
bumping, bubbles and liquid from being expelled.
| | | | | | |
*Vaseline*-Makes the join airtight and prevents them from freezing in certain
| | | | | | | | | |
reactions
|
How do you carry out "heating under reflux"? - correct answer ✔Set up the
| | | | | | | | | | | | |
equipment as shown in the diagram.
| | | | | |
Add the reaction mix into the flask with antibumping granules.
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Add grease/vaseline between the flask and condenser joint.
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Clamp the flask/condenser joint to ensure it doesn't fall.
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Connect the tubing (water in at the bottom out on top) and start the reflux.
| | | | | | | | | | | | | |
What is the purpose of reflux? - correct answer ✔It enables a liquid to be
| | | | | | | | | | | | | |
continually boiled whilst the reaction takes place. This prevents volatile
| | | | | | | | | |
components from escaping and the flask boiling dry.
| | | | | | | | |
The vapour rises in the inner tube till it meets the outer tube containing cold
| | | | | | | | | | | | | |
water.
| |
The vapour condenses and drips back into the falsk.
| | | | | | | |
,What equipment is needed to carry out "distillation"? - correct answer
| | | | | | | | | |
✔Equipment: Condenser (clamps etc), Pear-shaped flask, antibumping
| | | | | | |
granules, grease/vaseline, still head, receiver, screw-tap adaptor, thermometer
| | | | | | | |
and a heat source.
| | | |
How do you carry out "distillation"? - correct answer ✔Place the reaction
| | | | | | | | | | |
mixture in the pear shaped glass. Apply grease at the joints and put the
| | | | | | | | | | | | | |
quickfit apparatus together.
| | | |
Clamp the flask/still head joint and the condenser joint. Put a flask at the
| | | | | | | | | | | | |
bottom of the receiver. Grease is used to ensure the apparatus comes apart
| | | | | | | | | | | | |
easily. Cold water in at the bottom.
| | | | | | |
What is the purpose of distillation? - correct answer ✔To separate pure liquids
| | | | | | | | | | | |
from their impurities. Each liquid will have a specific boiling point (the lowest
| | | | | | | | | | | | |
will boil first and is more volatile). The vapour leaves the flask and enters into
| | | | | | | | | | | | | | |
the cold condenser, where it condenses and becomes a liquid.
| | | | | | | | | |
How can a organic products be purified? - correct answer ✔Using a separating
| | | | | | | | | | | |
funnel. Identify the organic layer by adding in H₂O, the organic layer will
| | | | | | | | | | | | |
remain the same size. After:
| | | | |
1.Ensure the separating funnel tap is closed.
| | | | | |
2.Pour the mixture into the funneland place a stopper. Begin to invert it.
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3.Place it in a clamp and allow it to settle. Add H₂O again to identify the
| | | | | | | | | | | | | | |
aqueous layer.
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4.Remove the stopper and allow the whole lower layer to leave the funnel.
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5.The organic product has been purified.
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,How can acids from organic products be purified? - correct answer ✔By adding
| | | | | | | | | | | |
aqueous sodium carbonate and shaking the mix in a separating funnel. The
| | | | | | | | | | | |
acid will react with the base to produce Co₂.
| | | | | | | | |
Bc of this the tap needs to be opened slowly and away from you to release any
| | | | | | | | | | | | | | | |
pressure built up.
| | |
Why do some organic products need to be dried? - correct answer ✔To remove
| | | | | | | | | | | | |
excess water a drying agent is used. Normally anhydrous salts are used
| | | | | | | | | | | |
(MgSO₄, CaCl₂), they readily take up water to become hydrated. The salts
| | | | | | | | | | | |
above are used for general drying and calcium chloride is used for dring
| | | | | | | | | | | | |
hydrocarbons.
|
How do you dry organic products? - correct answer ✔1.Add the product to a
| | | | | | | | | | | | |
conical flask
| |
2.Use a spatula to add some drying agent and swirl the mix gently.
| | | | | | | | | | | |
3.Place a stopper to prevent evaporation (10mins)
| | | | | |
4.Is the solid is lumped H₂O is still present - add more agent and repeat 2-3.
| | | | | | | | | | | | | | |
5.If a fine powder forms decant (gradually pour) the liquid from the solid into a
| | | | | | | | | | | | | |
another flask - the liquid should be clear.
| | | | | | | |
Why does redillation need to be carried out? - correct answer ✔Some organics
| | | | | | | | | | | |
have similar boiling points so the prepared sample may still have impurities.
| | | | | | | | | | | |
Distillation is done again, the same apparatus is cleaned and dried. The
| | | | | | | | | | | |
compound required is then distilled.
| | | | |
What are the reactions of an alkane? - correct answer ✔A haloalkane - using
| | | | | | | | | | | | |
UV (homolytic fission/free radical substitution)
| | | | |
, What are the reactions of an alkene? - correct answer ✔-Alkane - using a H₂
| | | | | | | | | | | | | |
and Ni catalyst
| | | |
-Haloalkane - using a hydrogen halide | | | | | |
-Alcohol- Using H₂0(g) and H₃PO₄ catalyst
| | | | |
What are the reactions of a primary alcohol? - correct answer ✔-Alkene - using
| | | | | | | | | | | | |
concentrated H₂SO₄
| |
-Haloalkane - NaHalide + H₂SO₄ | | | |
-Aldehyde - K₂Cr₂O₇/H₂SO₄ destil | | |
-Carboxylic acid - K₂Cr₂O₇/H₂SO₄ reflux | | | |
What are the reactions of a secondary alcohol? - correct answer ✔-Ketone-
| | | | | | | | | | |
K₂Cr₂O₇/H₂SO₄ reflux |
What are the reactions of a haloalkane? - correct answer ✔-Alcohol - NaOH is
| | | | | | | | | | | | |
heated under reflux.
| | |
How do you filter under pressure and what are its benefits? - correct answer
| | | | | | | | | | | | |
✔A buchner funnel and flask are used.
| | | | | | | |
Dissolve the impure solid into just the right amount of a warm, appropriate
| | | | | | | | | | | |
solvent (until a saturated solution is formed).
| | | | | | |
If the solution is not clear; filter the solution through a buchner funnel to
| | | | | | | | | | | | |
|remove any insoluble impurities.
| | |
Cool the solution, so that the product recrystallizes to leave the smaller
| | | | | | | | | | |
amounts of impurities in the solution.
| | | | | |
Filter the solution to recover the purified product.
| | | | | | |
exam with verified solutions
What is needed to carry out "heating under reflux"? - correct answer
| | | | | | | | | | |
✔Equipment: Vertical condenser (clamps etc), Pear-shaped flask, antibumping
| | | | | | | |
granules, grease/vaseline and a heat source
| | | | | |
*Antibumping granules*-used to make the liquid boil calmly and prevent
| | | | | | | | |
bumping, bubbles and liquid from being expelled.
| | | | | | |
*Vaseline*-Makes the join airtight and prevents them from freezing in certain
| | | | | | | | | |
reactions
|
How do you carry out "heating under reflux"? - correct answer ✔Set up the
| | | | | | | | | | | | |
equipment as shown in the diagram.
| | | | | |
Add the reaction mix into the flask with antibumping granules.
| | | | | | | | | |
Add grease/vaseline between the flask and condenser joint.
| | | | | | | |
Clamp the flask/condenser joint to ensure it doesn't fall.
| | | | | | | |
Connect the tubing (water in at the bottom out on top) and start the reflux.
| | | | | | | | | | | | | |
What is the purpose of reflux? - correct answer ✔It enables a liquid to be
| | | | | | | | | | | | | |
continually boiled whilst the reaction takes place. This prevents volatile
| | | | | | | | | |
components from escaping and the flask boiling dry.
| | | | | | | | |
The vapour rises in the inner tube till it meets the outer tube containing cold
| | | | | | | | | | | | | |
water.
| |
The vapour condenses and drips back into the falsk.
| | | | | | | |
,What equipment is needed to carry out "distillation"? - correct answer
| | | | | | | | | |
✔Equipment: Condenser (clamps etc), Pear-shaped flask, antibumping
| | | | | | |
granules, grease/vaseline, still head, receiver, screw-tap adaptor, thermometer
| | | | | | | |
and a heat source.
| | | |
How do you carry out "distillation"? - correct answer ✔Place the reaction
| | | | | | | | | | |
mixture in the pear shaped glass. Apply grease at the joints and put the
| | | | | | | | | | | | | |
quickfit apparatus together.
| | | |
Clamp the flask/still head joint and the condenser joint. Put a flask at the
| | | | | | | | | | | | |
bottom of the receiver. Grease is used to ensure the apparatus comes apart
| | | | | | | | | | | | |
easily. Cold water in at the bottom.
| | | | | | |
What is the purpose of distillation? - correct answer ✔To separate pure liquids
| | | | | | | | | | | |
from their impurities. Each liquid will have a specific boiling point (the lowest
| | | | | | | | | | | | |
will boil first and is more volatile). The vapour leaves the flask and enters into
| | | | | | | | | | | | | | |
the cold condenser, where it condenses and becomes a liquid.
| | | | | | | | | |
How can a organic products be purified? - correct answer ✔Using a separating
| | | | | | | | | | | |
funnel. Identify the organic layer by adding in H₂O, the organic layer will
| | | | | | | | | | | | |
remain the same size. After:
| | | | |
1.Ensure the separating funnel tap is closed.
| | | | | |
2.Pour the mixture into the funneland place a stopper. Begin to invert it.
| | | | | | | | | | | |
3.Place it in a clamp and allow it to settle. Add H₂O again to identify the
| | | | | | | | | | | | | | |
aqueous layer.
| |
4.Remove the stopper and allow the whole lower layer to leave the funnel.
| | | | | | | | | | | | |
5.The organic product has been purified.
| | | | |
,How can acids from organic products be purified? - correct answer ✔By adding
| | | | | | | | | | | |
aqueous sodium carbonate and shaking the mix in a separating funnel. The
| | | | | | | | | | | |
acid will react with the base to produce Co₂.
| | | | | | | | |
Bc of this the tap needs to be opened slowly and away from you to release any
| | | | | | | | | | | | | | | |
pressure built up.
| | |
Why do some organic products need to be dried? - correct answer ✔To remove
| | | | | | | | | | | | |
excess water a drying agent is used. Normally anhydrous salts are used
| | | | | | | | | | | |
(MgSO₄, CaCl₂), they readily take up water to become hydrated. The salts
| | | | | | | | | | | |
above are used for general drying and calcium chloride is used for dring
| | | | | | | | | | | | |
hydrocarbons.
|
How do you dry organic products? - correct answer ✔1.Add the product to a
| | | | | | | | | | | | |
conical flask
| |
2.Use a spatula to add some drying agent and swirl the mix gently.
| | | | | | | | | | | |
3.Place a stopper to prevent evaporation (10mins)
| | | | | |
4.Is the solid is lumped H₂O is still present - add more agent and repeat 2-3.
| | | | | | | | | | | | | | |
5.If a fine powder forms decant (gradually pour) the liquid from the solid into a
| | | | | | | | | | | | | |
another flask - the liquid should be clear.
| | | | | | | |
Why does redillation need to be carried out? - correct answer ✔Some organics
| | | | | | | | | | | |
have similar boiling points so the prepared sample may still have impurities.
| | | | | | | | | | | |
Distillation is done again, the same apparatus is cleaned and dried. The
| | | | | | | | | | | |
compound required is then distilled.
| | | | |
What are the reactions of an alkane? - correct answer ✔A haloalkane - using
| | | | | | | | | | | | |
UV (homolytic fission/free radical substitution)
| | | | |
, What are the reactions of an alkene? - correct answer ✔-Alkane - using a H₂
| | | | | | | | | | | | | |
and Ni catalyst
| | | |
-Haloalkane - using a hydrogen halide | | | | | |
-Alcohol- Using H₂0(g) and H₃PO₄ catalyst
| | | | |
What are the reactions of a primary alcohol? - correct answer ✔-Alkene - using
| | | | | | | | | | | | |
concentrated H₂SO₄
| |
-Haloalkane - NaHalide + H₂SO₄ | | | |
-Aldehyde - K₂Cr₂O₇/H₂SO₄ destil | | |
-Carboxylic acid - K₂Cr₂O₇/H₂SO₄ reflux | | | |
What are the reactions of a secondary alcohol? - correct answer ✔-Ketone-
| | | | | | | | | | |
K₂Cr₂O₇/H₂SO₄ reflux |
What are the reactions of a haloalkane? - correct answer ✔-Alcohol - NaOH is
| | | | | | | | | | | | |
heated under reflux.
| | |
How do you filter under pressure and what are its benefits? - correct answer
| | | | | | | | | | | | |
✔A buchner funnel and flask are used.
| | | | | | | |
Dissolve the impure solid into just the right amount of a warm, appropriate
| | | | | | | | | | | |
solvent (until a saturated solution is formed).
| | | | | | |
If the solution is not clear; filter the solution through a buchner funnel to
| | | | | | | | | | | | |
|remove any insoluble impurities.
| | |
Cool the solution, so that the product recrystallizes to leave the smaller
| | | | | | | | | | |
amounts of impurities in the solution.
| | | | | |
Filter the solution to recover the purified product.
| | | | | | |
