Chemistry

This is a Multiple Choice Questions as classified in NCERT Exemplar

Option (i) i.e., Ozone is not responsible for greenhouse effect is the answer since O3 is responsible for the greenhouse effect, its contribution is about 8%  to 10%. About 75% of the solar energy reaching the earth is absorbed by the earth's surface, which increases its temperature. The rest of the heat radiates back to the atmosphere while some of the heat is trapped by gases such as carbon dioxide, methane, ozone, chlorofluorocarbon compounds (CFCs) and water vapour in the atmosphere. Thus, they add to the heating of the atmosphere. This is the reason behind global warming.

This is a long answer type question as classified in NCERT Exemplar

When dissolved in suitable solvents, certain solutes/compounds either dissociate or associate. For instance, ethanoic acid dimerises in benzene due to hydrogen bonding, but dissociates and produces ions in water.

As a result, the number of chemical species in solution rises or falls in relation to the number of chemical species of solute used to create the solution. Because the magnitude of the colligative property is dependent on the number of solute particles in relation to the total number of particles in solution, it is expected that the molar mass calculated using colligative properties will be either higher or lower than the expected or normal value, and this is referred to as abnormal molar mass.

Van't Hoff established a factor called the Van't Hoff factor to account for the degree of dissociation or association of molecules in solution. It can be summed up as follows:

The predicted colligative qualities are achieved by assuming that the nonvolatile solute is neither associated nor dissociated, and anomalous molar mass is the empirically determined molar mass. The value of I (van't Hoff factor) is smaller than unity in the event of association, but greater than unity in the case of dissociation.

This is a long answer type question as classified in NCERT Exemplar

 (i) When egg is placed in a dilute mineral acid solution (preferably dilute HCl solution), the hard external CaCO₃ layer of the egg dissolves out /removed without damaging its semipermeable membrane.

(ii) Yes, this egg can be inserted into a bottle with a narrow neck without distorting in shape. The process involved utilising phenomenon of osmosis is explained as below -

Egg is placed in a mineral acid solution – after some time the egg is removed and placed in a hypertonic solution- size of the egg gradually decreases after some time and it shrivels due to osmosis. Since the egg has shrivelled it can now be inserted easily into a bottle with a narrow mouth. The egg is, therefore, placed in a bottle with a narrow neck & then a hypotonic solution is filled into this bottle. On adding hypotonic solution, the egg regains shape due to osmosis.

Hypertonic solution- is a solution with  higher salt concentration  than that of  the normal body cells so that the solvent/water is drawn out of the cell by osmosis or any solution with higher osmotic pressure  than another solution is called "Hypertonic solution".    

Hypotonic solution is a solution  with lower salt concentration than that of the normal body  cells so that water/solvent flows into the cell by osmosis or hypotonic solution is a solution which has lower osmotic pressure than the other solution. 

This is a long answer type question as classified in NCERT Exemplar

The process of osmosis is of immense biological and industrial importance as is evident from the following examples:

A. Biological Importance :

(i) Osmosis is responsible for some of the water movement from the soil into the plant roots and then into the top parts of the plant.

(ii) Adding salt to meat to protect it against bacterial action (ie. salting).

(iii) Sugar is used to protect fruits from bacterial attack. Bacterium in canned fruit shrivels and dies as a result of the osmosis process.

(iv) Salt blood cells break due to osmosis when placed in water containing less than 0.9 percent (mass by volume). Osmosis causes water retention in tissue cells and intercellular gaps in those who consume a lot of salt or eat salty foods. Edema is the name given to the puffiness or swelling that results as a result of this.

(v) When withered flowers are immersed in freshwater, they revive.

B. Industrial importance

(i) For desalination of seawater, reverse osmosis is used: when a pressure greater than osmotic pressure is applied to saltwater, clean water is squeezed out through a semipermeable membrane. For this, a number of semipermeable membranes are available.