DSE CHEM MEMORISING 1-35
1. Zinc oxide react with sulphuric acid, suggest how can know zinc oxide is in excess,
and why zinc oxide rather than sulphuric acid is used in excess. - answer1. Unreacted
ZnO(s) can be seen can proved it is in excess, and it used in excess because to ensure
that the product is not contaminated with sulphuric acid
2. Suggest ONE way to show that a saturated solution has been obtained. - answer2.
Remove a drop of the solution with a glass rod, and see whether any solid forms when
the drops cool.
3. Why little amount of cold distilled water is used to wash the crystal. - answer3.
Washing with distilled water can remove the water-soluble impurities.
4. Suggest ONE way of drying the crystals obtained. - answer4. Drying the crystals
between filer papers.
5. Why wine is an opened bottled will become unpalatable if left to stand for some time.
- answer5. Ethanol in wine can be oxidised by oxygen in air to give ethanal or ethanoic
acid.
6. Why argon is chemically unreactive? - answer6. The outermost shell of an argon
atom is a stable octet structure.
7. Why argon, instead of helium, is used in preserving wine. - answer7. Argon is denser
than air, it displaces air from the bottle and thus prevents the wine from contact air.
Helium is less dense than air, so it will not displace air.
8. Suggest ONE drawbacks of pumping air out from an opened bottle of wine and then
stoppering the bottle for wine preservation. - answer8. The substances with a pleasant
odour are volatile organic compounds. Pumping air out from the bottle may also remove
these substances.
9. Describe how 100.0cm3 aqueous solution ( of a soluble solid ) can be prepared. -
answer9. Dissolve the solid in some distilled water, and then transfer the solution to a
100.0cm3 volumetric flask. Wash the beaker with distilled water and transfer the
washings into the volumetric flask. Add distilled water up to the graduation mark of the
volumetric flask. Shake the volumetric flask to ensure its content is well mixed.
10. State ONE advantage of using kerosene as fuel for torch. - answer10. Kerosene
undergoes incomplete combustion to give a luminous flame which is more easily can be
seen.
1. Zinc oxide react with sulphuric acid, suggest how can know zinc oxide is in excess,
and why zinc oxide rather than sulphuric acid is used in excess. - answer1. Unreacted
ZnO(s) can be seen can proved it is in excess, and it used in excess because to ensure
that the product is not contaminated with sulphuric acid
2. Suggest ONE way to show that a saturated solution has been obtained. - answer2.
Remove a drop of the solution with a glass rod, and see whether any solid forms when
the drops cool.
3. Why little amount of cold distilled water is used to wash the crystal. - answer3.
Washing with distilled water can remove the water-soluble impurities.
4. Suggest ONE way of drying the crystals obtained. - answer4. Drying the crystals
between filer papers.
5. Why wine is an opened bottled will become unpalatable if left to stand for some time.
- answer5. Ethanol in wine can be oxidised by oxygen in air to give ethanal or ethanoic
acid.
6. Why argon is chemically unreactive? - answer6. The outermost shell of an argon
atom is a stable octet structure.
7. Why argon, instead of helium, is used in preserving wine. - answer7. Argon is denser
than air, it displaces air from the bottle and thus prevents the wine from contact air.
Helium is less dense than air, so it will not displace air.
8. Suggest ONE drawbacks of pumping air out from an opened bottle of wine and then
stoppering the bottle for wine preservation. - answer8. The substances with a pleasant
odour are volatile organic compounds. Pumping air out from the bottle may also remove
these substances.
9. Describe how 100.0cm3 aqueous solution ( of a soluble solid ) can be prepared. -
answer9. Dissolve the solid in some distilled water, and then transfer the solution to a
100.0cm3 volumetric flask. Wash the beaker with distilled water and transfer the
washings into the volumetric flask. Add distilled water up to the graduation mark of the
volumetric flask. Shake the volumetric flask to ensure its content is well mixed.
10. State ONE advantage of using kerosene as fuel for torch. - answer10. Kerosene
undergoes incomplete combustion to give a luminous flame which is more easily can be
seen.
