Hot saturated solution of sodium nitrate forms crystals as it cools. Why?
Answer
Solubility of sodium nitrate decreases with a fall in temperature. Thus, when a hot saturated solution of sodium nitrate cools, it forms crystals as it separates from the solution.
Henry's law: At any given temperature, the mass of a gas dissolved in a fixed volume of a liquid or solution is directly proportional to the pressure on the surface of a liquid.
Explain why a hot saturated solution of potassium nitrate forms crystals as it cools.
Answer
Solubility of nitrates decreases with a fall in temperature. Thus, when a hot saturated solution of potassium nitrate cools, it forms crystals as it separates from the solution.
In which of the following substances will there be No change in mass when they are exposed to air? Sodium chloride Iron Conc. sulphuric acid Table salt Sodium carbonate crystals
Normally, solubility of crystalline solid increases with temperature. Does it increase uniformly in all cases? Name a substance whose solubility: Initially increases then decreases with rise in temperature.
Normally, solubility of crystalline solid increases with temperature. Does it increase uniformly in all cases? Name a substance whose solubility: Increases slightly with temperature.
Normally, solubility of crystalline solid increases with temperature. Does it increase uniformly in all cases? Name a substance whose solubility: Increases gradually with temperature.
Normally, solubility of crystalline solid increases with temperature. Does it increase uniformly in all cases? Name a substance whose solubility: Increases rapidly with temperature
Explain why:
Fused $CaCl _2$ or conc. $H _2 SO _4$ is used in a desiccator.
Answer
Fused $CaCl _2$ or concentrated $H _2 SO _4$ is deliquescent in nature, i.e. it absorbs moisture, and hence, these are used in desiccators as drying agents.
Explain why: The solute cannot be separated from a solution by filtration.
Answer
The component which dissolves in a solvent is known as a solute. So, it cannot be separated from a solution by filtration. However, filtration is used when the solute is insoluble in the solution.
Explain why: Lakes and rivers do not suddenly freeze in the winters.
Answer
Lakes and rivers do not freeze suddenly in winters because of the high specific latent heat of solidification, i.e. the amount of heat released when 1 g of water solidifies to form 1 g of ice at 0°C. It is about 336 J/g or 80 cal/g.
Explain why: A solution is always clear and transparent.
Answer
A water-soluble solid disappears in a solution where the solvent is water, and water has the property of being clear and transparent. So, the solution is also clear and transparent.
Which test will you carry out to find out if a given solution is saturated or unsaturated or supersaturated?
Answer
1. A solution in which more of a solute can be dissolved at a given temperature is an unsaturated solution. 2.A solution in which no more solute can be dissolved at a given temperature is a saturated solution at that temperature. 3. A solution in which some solute separates on cooling slightly is a super saturated solution.
How is aquatic life benefited by the fact that water has maximum density at $4^oC?$
Answer
The property of anomalous expansion of water enables aquatic life to exist because water freezes on the surface of the water body, but it is still liquid below the ice layer.
What is the effect of impurities present in the water on the melting point and boiling point of water?
Answer
The boiling point of water increases due to the presence of dissolved impurities. The freezing point of water decreases due to the presence of dissolved impurities.
Explain why: If distilled water is kept in a sealed bottle for a long time, it leaves etchings on the surface of the glass.
Answer
If distilled water is kept in a sealed bottle for a long time, it etches the surface of glass because substances which are apparently insoluble in water actually dissolve in minute traces in water.
Explain why:
Ice at zero degrees centigrade has greater cooling effect than water at $0^oC.$
Answer
Ice at $0^{\circ} C$ gives more cooling effect than water at $0^{\circ} C$ because at $0^{\circ} C$ ice absorbs 336 J per gram of energy to melt to $0^{\circ} C$ water.