Que 2B) III.write short notes. (2m each)
1. Escape Velocity
Ans.
(1) The minimum velocity with which a body should be projected from the surface of a planet or moon, so that it escapes from the gravitational influence of the planet or moon is called as escape velocity.
(ii) Escape velocity is given as,
, where M is mass of the planet, R is radius of the planet and g is acceleration due to gravity of the planet.
(iii) The escape velocity is different for different planets.
2. Free Fall
Ans.
(1) The motion of any object under the influence of the force of gravity alone is called as free fall.
(2) In free fall, the initial velocity of the object is zero and goes on increasing due to the acceleration due to gravity of the earth.
(3) During free fall, the frictional force due to air opposes the motion of the object and a buoyant force also acts on the object.
(4) Thus, true free fall is possible only in vacuum.
3. Anomalous behaviour of water
Ans
(1) Normally, liquids expand on heating and contract on cooling. But water exhibits an exceptional behaviour in temperature range of 0 °C to 4 °C.
(2) When water is heated from 0 °C up to 4 °C, instead of expanding it contracts. Its volume decreases continuously from 0 °C to 4 °C. At 4 °C, its volume is minimum.
(3) Upon heating further, however, it expands and its volume increases.
(4) This behaviour of water between temperature interval of 0 °C to 4 °C is called anomalous behaviour of water.
4. Specific heat capacity
Ans.
(1) The amount of heat energy required to raise the temperature of a unit mass of an object by 1 °C is called the specific heat or specific heat capacity of that object.
(2) SI unit of specific heat capacity is J/kg °C and CGS unit is cal/g °C
(3) It is denoted by ‘c’ and given by formula: mAT
(4) Specific heat is a property of a substance and is different for different substances.
5. Dew point temperature
Ans.
(1) When unsaturated air (of specific volume) at a certain temperature is taken and its temperature is decreased, a temperature is reached at which the air becomes saturated with vapour. This temperature is called the dew point temperature.
(2) Relative humidity of air at dew point is 100%.
(3) Dew drops, condensation of water droplets on the surface of water bottle taken out from refrigerator are some visible examples of air having reached dew point temperature.
6. Regelation
Ans.
(1) The phenomenon in which the ice converts to liquid due to applied pressure and then reconverts to ice once the pressure is removed is called regelation.
(2) Due to applied pressure, melting point of ice is lowered below 0 °C. As a result, ice gets converted into water at 0 °C.
(3) When the applied pressure is removed, the melting point is restored to 0 °C and water gets re-converted into ice.
(4) Preparation of ice balls uses phenomenon of regelation. The shredded ice is pressurised around the tip of the stick and then due to regelation gets re-freezed in the form of single solid ice ball.
7. Catenation power
Ans.
(1) The unique property of carbon atom to form covalent bonds with other carbon atoms giving rise to extremely big molecules is called catenation power.
(2) The covalent bond between two carbon atoms is strong and stable.
(3) This is the reason carbon is bestowed with catenation power.
(4) Due to catenation power, carbon can form large number of compounds containing open chains or closed chains of carbon atoms.
8. Characteristics of carbon
Ans.
(1) Catenation power: Carbon has a unique ability to form strong covalent bonds with other carbon atoms; this results in formation of big molecules. This property of carbon is called catenation power.
(2) Multiple bond formation: Two carbon atoms can be bonded together by one, two or three covalent bonds. These are called single bond, double bond, and triple bond respectively. Thus, carbon atom has the ability to form multiple bonds as well as single bonds.
(3) Tetravalency: Being tetravalent one carbon atom can form bonds with four other atoms (carbon or any other). This results in formation of many compounds.
(4) Isomerism: One more characteristics of carbon, which is responsible for large number of carbon compounds is isomerism.
9. Functional groups in carbon compounds
Ans.
(1) Many more types of carbon compounds are formed by formation of bonds of carbon with other elements such as halogens, oxygen, nitrogen, sulphur.
(2) The atoms of these elements (hetero atoms) substitute one or more hydrogen atoms in the hydrocarbon chain and thereby the tetravalency of carbon is satisfied.
(3) The compound acquire specific chemical properties due to these hetero atoms or the groups of atoms that contain heteroatoms, irrespective of the length and nature of the carbon chain in that compound.
(4) Therefore, these hetero atoms or the groups of atoms containing hetero atoms are called functional groups.
E.g. In CH3 – OH, –OH (alcohol) is the functional group containing heteroatom ‘oxygen’.
10. Homologous series
Ans.
(1) The series of carbon compounds formed by joining the same functional group in the place of a particular hydrogen atom on the carbon chains having sequentially increasing length is called homologous series.
(2) There are different homologous series in accordance with the functional group. For example, homologous series of alcohols, homologous series of carboxylic acids, homologous series of aldehydes, etc.
(3) All the members of the homologous series are homologues of each other and they can be represented by the same a general molecular formula.
(4) Physical properties generally show a gradual change with increase in molecular mass in the series whereas chemical properties of the members of the series show similarity because of the presence of the same functional group in them.
11. Aromatic hydrocarbons
Ans.
(1) Benzene is a cyclic unsaturated hydrocarbon. Its molecular formula is C6H6.
(2) It has three alternate double bonds in its six membered ring structure.
(3) Structural formula of benzene:
(4) Compounds having such characteristic unit in their structures are called aromatic compounds or aromatic hydrocarbons.
12. Moon missions
Ans.
(1) Moon is the closest astronomical object to earth, hence the first space missions to objects in the solar system were the missions to the moon. Such missions have so far been executed by USA, Soviet Union, European countries, China, Japan and India.
(2) The space crafts in the Luna series sent by Soviet Union reached near the moon. Luna 2, launched in 1959 was first such craft. After that, till 1975, 15 space crafts made chemical analysis of the moon and also measured its gravity, density and radiations. Last four crafts even landed on the moon and brought the samples of stones on the moon for analysis in the laboratories. All these missions were unmanned.
(3) America also executed moon missions from 1962 to 1972. The specialty of these missions was that some of these were manned missions.
(4) In July, 1969, Neil Armstrong became the first human to step on the moon. In 2008, Indian Space Research Organization (ISRO) successfully launched Chandrayaan- 1 and placed it into an orbit around the moon. It sent useful information to earth for about a year.