Science [2 Mark Questions]

The wood is burnt in the limited supply of air to obtain charcoal. When wood is burnt in the limited supply of oxygen, water and volatile materials are removed and charcoal is left behind as the residue. Charcoal is considered a better fuel than wood because:

1. It has higher heat generation efficiency.
2. It produces less smoke.
3. It leaves very less residue behind.

Acetic acid is a weak acid. The following changes will occur when a few drops of acetic acid are added to the given solutions:

1. Phenolphthalein remains colorless, as acetic acid shows a change in colour in basic substances.
2. Acetic acid dissolved in water.
3. Acetic acid turns the colour of the universal indicator to pale orange.
4. When added to sodium hydrogen carbonate powder, acetic acid causes effervescence because of the evolution of carbon dioxide gas in the process.

Sodium metal test: Add a small piece of sodium metal to the organic liquid (to be tested), taken in a dry test tube. If bubbles (or effervescence) of hydrogen gas are produced, it indicates that the given organic liquid is an alcohol.

1. All the members of the homologous series can be represented by the same general formula.
2. Any two adjacent homologues differ by 1 carbon atom and 2 hydrogen atoms in their molecular formulae.

Due to the presence of free electrons in a graphite crystal, it conducts electricity however; a diamond crystal does not have free electrons so it does not conduct electricity.

When methanol is consumed, it is oxidised to methanal in the liver. Methanal reacts rapidly with the components of cell, leading to the coagulation of protoplasm. Consumption of methanol can also damage the optic nerve, resulting in blindness.

Unsaturated hydrocarbon contains either double or triple bonds, which are reactive, so they break easily and convert into single covalent bonds hence they easily undergo addition reactions.

Uses of ethanol:

1. It is used in the manufacture of paints, varnishes, lacquers, medicines, perfumes, dyes, soaps and synthetic rubber.
2. It is used as a solvent. Many organic compounds which are insoluble in water are soluble in ethyl alcohol.

Carbon has 4 electrons in its valence shell. To attain stability, it should either gain 4 electrons or lose 4 electrons. It cannot lose 4 electrons as it involves a lot of energy. Also, it cannot gain 4 electrons because the nucleus cannot hold on to the four extra electrons added. Therefore, to complete the octet, it shares 4 electrons with other atoms. That is why, carbon forms compounds mainly by covalent bonding.

A detergent is the sodium salt of long chain benzene sulphonic acid which has cleansing properties in water.
Example: Sodium n-dodecyl benzene sulphonate.

Carbon forms a large number of carbon compounds because carbon atoms can link with one another by means of covalent bonds to form long chains of carbon atoms.

When soap is used for washing clothes with hard water, a large amount of soap in water is reacting with the calcium and magnesium ions of hard water to form an insoluble precipitate called scum, before it can be used for the real purpose of washing.

Common salt is added to the mixture to make the soap come out of solution. Though most of the soap separates out on its own but some of it remains in solution. Common salt is added to precipitate out all the soap from the aqueous solution.

	Soaps		Sodium metal
1.	Soap are made from fat and alkali by specification method.	1.	Detergents are carbonic compounds which are not alkaline.
2.	There are cheap.	2.	They are costly.
3.	There are not suitable for delicate clothes.	3.	They are suitable for delicate clothes.
4.	They are clean better in hot water.	4.	They clean both in hot and cold water.
5.	They don’t produce lather with hard water and are not able to clean the cloth.	5.	They clean the cloth even in hard water.

Ethanol is harmful for drinking. Drinking ethanol in small amounts causes drunkenness. If it is consumed in large quantities, then it can slow down metabolic processes and affect the central nervous system. This will lead to lack of coordination, mental confusion, stupour etc.

Diamond has a high melting point because a lot of heat energy is required to break the network of strong covalent bonds in the diamond crystal.

1. Carboxylic acid group.
2. Aldehyde group.
3. Alcohol group.
4. Ketone group.

Graphite is a good conductor of electricity. Its structure is the main reason for this property. Each carbon atom in graphite is directly linked to only three carbon atoms through covalent bonds. Therefore, out of the four valence electrons in a carbon atom, only three are used for bonding and the fourth is relatively free and can move from one carbon atom to the other. These free electrons make graphite a good conductor of electricity and also a good lubricant.

Ethene decolourises bromine water because ethene is an alkene. And all alkenes and alkynes are unsaturated compounds which decolourise bromine water. On the other hand, ethane being an alkane is a saturated compound which does not decolourise bromine water.

The most unique property of carbon atom is its ability to combine itself, atom to atom to form long chains. This property of self combination is useful to us because it gives rise to an extremely large number of carbon compounds (or organic compounds).

Coal and petroleum are called fossil fuels because they are produced through the decomposition of the pre-historic organisms (plants and animals) buried deep in the soil since millions of years ago.

Examples of fuel include wood, coal, natural gas, and oil.Combustion is where you burn a fuel in the presence of an oxidant like oxygen. Heat is produced, because the bonds in thefuel store more energy than the bonds in the water and carbon dioxide that are the products of combustion. As a result, the bonds present in the molecules of fuel break, releasing energy. Sometimes, the energy released falls in the visible range of the electromagnetic spectrum (which means the energy released is visible to human eye) which we call as light. Sometimes the energy released falls under infrared region, which we commonly call as heat. Basically, the compounds generate heat or light or both due to the release of energy from the breaking of molecular bonds.

Soap is mixed with water to form micelle which gives the solution a cloudy appearance when soap is added to the water the fatty acid ionizes. The polar water soluble gets attracted to water while the non-polar tails attract each other. Then the ions are attracted to each other and form the special clusters and sometimes in a form of emulsions which gives a cloudy look.