IGCSE Chemistry Paper-1: Specimen Questions with Answers 96 - 97 of 99
Question number: 96
Question
A substance X has the following properties. Name X.
- hardest substance known to man
- brittle (not malleable)
- insulator (non-conductor)
- insoluble in water
- very high melting point
Choices
| Choice (4) | Response | |
|---|---|---|
| a. | Graphite |
|
| b. | Diamond |
|
| c. | Fullerenes |
|
| d. | None of the above |
|
Answer
b.Explanation
Diamond has strong covalent bonds holding the structure together. All of the bonds are directional and stress will tend to break the structure (In a malleable substance, such as for example a metal, the bonding is non-directional and can still act if the particles are displaced with respect to one another).
All of the valence (outer shell) electrons are used in bonding. The bonds are sigma and the electrons are located between the two carbon nuclei being bonded together. None of the electrons are free to move.
There are only very weak Van der Waal’s attractions between the carbon atoms and the water molecules whereas the carbon atoms are bonded very tightly to one another.
Many strong covalent bonds holding the structure together - it requires massive amounts of energy to pull it apart
Question number: 97
Question
ph of some solutions is given in below table. What would be the nature of the substance.
| S. No. | Solution | App pH value |
| 1 | Coffee | 4.5 - 5.5 |
| 2 | Soapy water | 12 |
| 3 | Saliva | 6.5 – 7.5 |
| 4 | Battery acid | 0 |
Choices
| Choice (4) | Response | |
|---|---|---|
| a. | 1- Basic, 2- Neutral, 3 –Neutral, 4 –Acidic |
|
| b. | 1- Basic, 2- Acidic, 3 –Neutral, 4 -Acidic |
|
| c. | 1- Acidic, 2- Basic, 3 –Neutral, 4 -Acidic |
|
| d. | 1- Basic, 2- Neutral, 3 –Neutral, 4 -Basic |
|
Answer
c.Explanation
pH is a numeric scale used to specify the acidity or alkalinity of an aqueous solution Solutions with a pH less than 7 are acidic and solutions with a pH greater than 7 are alkaline or basic. Pure water is neutral, being neither an acid nor a base. Contrary to popular belief, the pH value can be less than 0 or greater than 14 for very strong acids and bases respectively.