FRANK Solutions for Class 9 Chemistry Chapter 6 - Water
Chapter 6 - Water Exercise 96
(b) Name two gases that are dissolved in water and state the significance of each to aquatic organisms.
(a) In the plant body
(b) In the human body.
(b) Water constitutes 3/4th of our human body and it is necessary for the survival of human beings and being the universal solvent helps in transportation and also regulates the body temperature.It also contains dissolved salts which supply essential minerals which are necessary for our body.
At 40C, water has its maximum density and minimum volume. At any temperatur above or below 4 C, the density of water decreases. This property is called anomalous expansion of water. The significance of this unique property of water is that it enables marine life to exist in the colder regions of the world, because even when water freezes on the top, it is still liquid below the ice layer.
1. Water molecule can form hydrogen bonds with the molecules of other compounds.
2. Water molecule is polar in nature.
(b) If a salt is dissolved in water, state its effect on
(i) Boiling point of water (ii) Freezing point of water
(iii) Density of water
i. Pure water is colourless, transparent, odourless and tasteless liquid.
ii. Boiling and Freezing points: At normal atmospheric pressure water boils at 100oC and freezes at 0oC.
iii. Pure water being a covalent compound is a very poor conductor of heat and electricity.On addition of electrolytes it becomes a good conductor of heat and electricity.
iv. Solvent properties:Water is a remarkable solvent dissolves many substances forming aqueous solutions because of its high dielectric constant.
v. Anomalous behavior: On cooling water contracts in volume, as do other liquids, but at 4o C, it starts expanding, and continues to do till the temperature reaches 0oC,the point at which it converts to ice.
i. Boiling point of water: It increases with the addition of salt in water.
ii. Freezing point of water: It decreases with the addition of salt in water.
iii. Density of water: It increases with the addition of salt in water.
(a) Metal oxides
(b) Non-metallic oxides
b. Water reacts with non metals oxides: corresponding acids are formed.
(a) Calcium oxide (b) Sulphur trioxide
(c) Phosphorous pentoxide (d) Sulphur dioxide
1. Measuring its boiling point, if comes out to be 100oC then it confirms the liquid to be water.
2. Measuring its melting point, if comes out to be 0oC then it confirms the liquid to be water.
Chapter 6 - Water Exercise 97
(a) A piece of Na is added to cold water.
(b) A piece of Ca is added to cold water.
(c) A coil of Mg is heated in steam.
(b) solids, and
(c) gases, which dissolve in water.
(b) Solids: Sugar, urea
(c) Gases: Oxygen, carbon dioxide
(b) A gas in a liquid: Solubility decreases with rise in temperature.Thus, gases dissolves readily in cold water than in hot water.
(a) Ice floats on water.
(b) A saturated solution becomes unsaturated when heated.
(c) Hot water contains less dissolved air than cold water.
(b) A solution is said to be saturated if at a particular temperature if no more of the solute can be dissolved in it at that temperature, when the temperature is increased more solute particles can be dissolved in that saturated solution as the solubility of most of the substances generally increases with rise in temperature and thereby making it unsaturated.
(c) Solubility of gases decreases with increase in temperature hence hot water contains less dissolved air than cold water.
(b) Solvent: It is the medium in which the solute dissolves.
(c) Solution: A homogeneous mixture that has a uniform composition throughout the volume of the mixture. It is the medium in which the solute dissolves.
(a) A saturated solution is warmed.
(b) A hot saturated solution is cooled.
(c) Some more of the solvent is added to a saturated solution.
(b) When a hot saturated solution is cooled slowly and is kept undisturbed the excess salt does not separates out . Thus the solution becomes a supersaturated solution which contains more solute in it than it can hold at room temperature.
(c) When the quantity of solvent increases,greater amount of solute can be dissolved.
1. Size of particles: Smaller the size of particles of the solute, greater is the solubility.
2. Contact between solute and the solvent: Increased contact between the solute and the solvent increases the solubility.
3. Temperature: The variation of solubility with temperature depends on its nature i.e. whether the reaction is exothermic or endothermic.
For exothermic reactions-The solubility decreases on increasing the temperature.
For endothermic reaction-The solubility increases on increasing the temperature.
At a constant temperature, the amount of a given gas that dissolves in a given type and volume of liquid is directly proportional to the partial pressure of that gas in equilibrium with that liquid.
Answer the following questions about X, Y and Z:
(i) Which of the metals X, Y or Z will be found free in nature?
(ii) Out of X and Z, which metal will combine with oxygen readily and with ease?
(iii) Write down the symbol of one of the metals (X, Y or Z) whose oxide is a strong base.
(iv) Write down the symbol of one of the metals (X, Y or Z) whose hydroxide is coloured.
(v) Write down the symbol of one of the metals (X, Y or Z) whose oxide cannot be reduced by hydrogen or carbon to give the metal.
(vi) Explain, what you would expect to see if a piece of Y was dipped into a solution of copper nitrate for a few minutes and withdrawn and examined.
(ii) X is more reactive so it will react with oxygen more readily and with ease.
(iv) Y is iron whose oxide is brown coloured Fe2O3.
(vi) The piece of Y i.e., iron is more reactive then copper so it will displace copper from copper nitrate and a brown layer of copper will be developed on the iron piece.
1. This is because an unsaturated solution will be able to take in more solute, so it dissolves the crystal.
2. A saturated solution will not take in more solute but will also not deposit any solute so the crystal stays the same size.
3. A supersaturated solution wants to deposit its excess solute and become saturated, it just needs something to start it along. The crystal starts it up and it will deposit its excess solute onto the crystal making the crystal bigger.
Chapter 6 - Water Exercise 98
(a) Increase in weight
(b) Decrease in weight
(c) No change in weight, when exposed to air?
(i) Sodium chloride
(iii) Conc. Sulphuric acid
(iv) Sodium carbonate crystals
(b) Decrease in weight: iron when exposed to air gets rusted due to the presence of moisture in the air it gets corroded, and hence its weight is reduced.
(c) No effect on weight: when conc. Sulphuric acid when exposed to air does not react and no change occurs in weight.
Ground water pollutants: Septic tanks, industry by products like pesticides, fertilizers, tanneries, mining wastes.
Surface water pollutants: No. of gases present in atmosphere like SO2, CO2, H2S, NOx, CO, etc., pollute surface water.
Lake water pollutant: organic wastes from hills, toxic effluents from urban areas, industrial effluents, dumping of huge amounts of sediments etc.,
River water pollutants: Industrial discharge, sewage discharges, detergents, discharges from drug, paper, and textile industries
Marine water pollutant: major pollutant is oil spills.
1. Natural process: Washing away of decomposed and animal wastes into main stream of water.
2. Human activity:
(a) Discharge of Household detergents: detergents used as a cleaning agent produce foam and pollute water. They do not undergo bio-degradation.
(b) Discharge of industrial effluents:Industrial activities generate a variety of waste products which are generally discharged into water streams.The pollutants associated with the industrial effluents are organic matter, inorganic dissolved salts, suspended solids. They inhibit oxidation or organic compounds; stabilize the colloidal impurities which do not aggregate to settle down.
(c) Sewage: Sewage is cloudy dilute aqueous solution containing minerals and organic matter.Sewage from homes and industries contains decomposable organic matter ,inorganic cations and anions,toxic metals etc.Pouring the drains and sewers in fresh water bodies causes water pollution.
Water pollution due to sewage creates the following problems:
1. Self purifying ability of water is lost and it becomes unfit for domestic purpose.
2. Self regulatory capabilities of aquatic organism is retarded.
3. Sewages produce pathogens which are diseases causing bacteria and result in water born gastro-intestinal diseases.
1. Primary treatment: The primary treatment involves physico-chemical processes to reduce settle able suspended solids of the wastes water and smoothened out individual effluent flow variations.It involves physic-chemical processes such as sedimentation,aeration,adsorption,oxidation etc.
2. Secondary treatment: In this, the dissolved and colloidal organic matter present in waste is removed by biological processes involving bacteria and other micro organisms.
These process may be aerobic or anaerobic.
Aerobic treatment: Purification is carried out by aerobes in the presence of molecular oxygen.
Anaerobic treatment: Purification of waste is achieved by anaerobes in complete absence of molecular oxygen.
3. Tertiary treatment: It is the final treatment for polishing the effluents from secondary treatment. By this process suspended solids are removed, bacteria are removed, and organic and inorganic solids are removed.
2. Bacterial dysentery
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