Chemistry Class 10 Chapter 15 Important Questions Answers 2023

Chemistry Class 10 Chapter 15 Important Questions Answers 2023

Chemistry Class 10 Chapter 15 Important Questions Answers 2023


WATER Important Q/As

water bubbles under the sea
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Question .1

What is the occurrence of water around the world?


The primary component of streams, oceans, and lakes on the surface of the world is water, a colorless, transparent molecule. It is a crucial fluid that is essential to maintaining life on Earth. Water has the chemical formula H2O. Covalent bonds hold two hydrogen atoms and one oxygen atom, which make up its composition, together. This fluid covers 71% of the surface of the globe.

Water is dispersed quite unevenly throughout the surface of the Earth. Fresh water makes up only 3% of the water on the surface; the other 97% is found in the ocean. Less than 1% of freshwater is found in lakes, rivers, and marshes, while 69% of it is found in glaciers and 30% is found underground. By another measure, only 1% of the water on Earth’s surface is suitable for human use, and 99% of that water is found underground.


Why is water important?


Importance of Water

1. The temperature of the Earth’s surface would be considerably lower if it weren’t for the high specific heat of the water. Life would find it impossible to survive as a result.

2. The heat from the sun is absorbed by the water in the oceans of the Earth throughout the day, keeping the temperature steady at night.

3. Since water is required to irrigate crops, it plays a crucial role in agriculture.

4. Since it boils at a temperature of 1000C, it is frequently used in cooking.

5. Water is used by humans for a variety of home tasks like washing and cleaning.

Additionally, freight can be transported over water. Ships are used to transfer a lot of products between the continents of the Earth.

Severe dehydration caused by a lack of water in the human body frequently leads to kidney failure, seizures, and brain edema.

The body’s ability to circulate oxygen is improved by water.

Additionally, it is very important for food digestion.

Saliva is made up primarily of water, which is crucial for the digestion of meals.

Water is necessary for the body to excrete waste. Kidney stones may develop as a result of the body not having enough water, which puts more strain on the kidneys.


What are some examples of properties of water?


Properties of Water

The world appears blue when viewed from space. Since water occupies a huge portion of the world, this blue space is water. Since we depend on water for everything.

  • Drinking
  • Bathing
  • Cooking, etc.

We must understand some of its characteristics.

  • The human body contains 65% water. The survival of life on earth depends on water. The earth’s surface is unevenly covered in water. It dissolves practically all polar solutes and creates a significant solvent.

Let’s examine its characteristics in order to comprehend its significance:

  • A tasteless and colorless liquid, water has neither. Water molecules form hydrogen bonds, giving the condensed form of the substance remarkable features. High melting and boiling points are also a result of this.
  • Water has greater specific heat, thermal conductivity, surface tension, dipole moment, and other properties than other liquids. Its importance to the biosphere results from these characteristics.
  • Water is a great solvent, thus it facilitates the movement of the ions and molecules needed for metabolism. Because of its high latent heat of vaporization, it aids in controlling body temperature.

1. Hydrogen bonds hold the molecules of water together. 2. Water has a boiling temperature of 100 °C and a melting point of 0 °C, respectively.

3. Water can exist in three different states: solids, liquids, and gases.

4. Water is known as the universal solvent because of its polar nature, which allows it to dissolve practically any substance.

5. Water has a crystalline structure in its solid state that resembles a three-dimensional cage.

6. Due to the numerous gaps in the crystalline structure of water, ice can float on water because it has a lower density than water. At 4° C, water has a known density of.0.99 g/ml.


How is water formed?


  • Composition of Water

Hydrogen and oxygen gases are produced when water is electrolyzed. The electrolytic cell is made up of two platinum electrodes that are submerged in water that has a small amount of an electrolyte, like H2SO4, added. The absence of ions in pure water prevents it from carrying enough charge, hence an electrolyte is required. Water changes to oxygen and H+ ions at the anode. Water is converted into H2 gas and OH ions at the cathode.

2H2O→ 2H2+O2


Why is water a solvent?


Water as a Solvent

Water is regarded as an all-purpose solvent. Here is an explanation of the qualities that make water effective at dissolving other substances, as well as why it is referred to as the universal solvent.

Because it dissolves more things than any other chemical, water is known as the universal solvent. This is referred to how polar each water molecule is. Each water (H2O) molecule has a charge on its side of hydrogen, which is slightly positive, and on the side of oxygen, which is slightly negative. It facilitates the separation of ionic substances into their positive and negative ions in water. Ionic compounds are attracted to the oxygen side of water by their positive parts, and their negative parts are drawn to the hydrogen side.

  • Example

Think about how salt dissolves in water as an example. NaCl, or salt, is sodium chloride. The compounds have a positive charge in the sodium section and a negative charge in the chlorine portion. There is an ionic link tying the two ions together. On the other hand, covalent bonds hold the hydrogen and oxygen together in the water. Hydrogen bonds also link the hydrogen and oxygen atoms in certain water molecules. When water and salt are combined, the water molecules orient so that the positively charged hydrogen cations face the chloride ion and the negatively charged oxygen anions face the sodium ion. Despite the strength of ionic connections, the overall effect of the polarity of all the water molecules is sufficient to draw the sodium and chlorine ions to their respective poles.


What are soft water and hard water, explain with examples.


  • Soft Water

Surface water that has low ion concentrations, especially low levels of calcium and magnesium ions, is referred to as soft water.

Wherever a river’s drainage basin and runoff are formed, rough, impermeable, and calcium-poor rocks naturally produce soft water.

Additionally, the phrase “soft water” is frequently used to describe water produced via a water-softening procedure (although it is more practical to refer to these water samples as softened water). In these circumstances, the water may also have high quantities of sodium and bicarbonate ion.

The water which easily forms a lather when treated with soap is called soft water.

  • Hard Water

The word “hard water” refers to water with a very high mineral concentration; it is the reverse of “soft water.” Hard water is created when water percolates into calcareous, gypsum, or chalk deposits that are largely made of bicarbonates, sulphates, and magnesium or calcium carbonates.

The concentration of multivalent cations in a given water sample often serves as a measure of its hardness. The metal complexes known as multivalent cations always have positive charges with a magnitude larger than 1+. Normally, the cations have a positive charge of 2+. Certain specific cations are very prevalent in hard water. Examples of this kind of cation include Ca2 + and Mg2 +. Leaching of minerals can allow these ions to infiltrate a water reservoir within an aquifer. Gypsum and calcite are two typical calcium-containing minerals. Dolomite is a typical magnesium mineral and contains calcium as well. Due to their low ion content, rainwater and filtered water are regarded as soft water samples.

Hard water usually doesn’t give a lather when mixed with soap.

CaCO3 + H2CO3→ Ca [HCO3]

MgCO3 + H2CO3→ Mg [HCO3]


What are the different types of hardness of the water?


Types of Water Hardness

Hardness is divided into 2 types temporary and permanent.

  • Temporary Hardness

Temporary hardness of the water is a term used to describe a sort of water hardness brought on by the presence of dissolved bicarbonate minerals, including ionic salts like calcium and magnesium bicarbonate. These minerals are known to separate into calcium and magnesium cations (represented by the symbols Ca2+ and Mg2+) and anions of the carbonate and bicarbonate when dissolved in water. The hardness of the water sample is caused by the presence of cations in the metal.

This sort of “temporary” hardness of water can be reduced by either boiling the water or by adding lime (also known as calcium hydroxide) via the lime softening process, unlike the type of hardness known as permanent hardness, which is typically brought on by sulfate and chloride compounds. Boiling the water helps calcium carbonate precipitate from its solution and helps carbonate develop from bicarbonate. After boiling, the temporarily hard water is cooled, and the result is soft water.

  • Permanent Hardness

It is typically challenging to remove boiling the permanent hardness of water, which is typically attributed to the mineral concentration in the water. When this occurs, it’s usually because particular salts, like calcium chloride or calcium sulphate, or magnesium chloride or magnesium sulphate, are present in the water. It should be observed that as the temperature rises, these are the salts that do not precipitate out (and cannot be extracted by simply boiling the water). To remove the ions that result in long-lasting water hardness and produce soft water, utilize a water softener or an ion exchange column.


Describe the methods to remove the hardness of the water.


Removal of Temporary Hardness

  • Boiling

Boiling can be used to treat temporary hard water that is devoid of calcium and magnesium sulfate components. The dissolved bicarbonate [Ca(HCO3)2] in the water changes throughout the boiling process into an insoluble carbonate (CaCO3) that settles at the bottom and can be removed later through filtering. Magnesium bicarbonate [Mg(HCO3)2] operates on the same guiding principle.

Unfortunately, this method is too expensive.

  • Clarks Method

Additionally, by using Clark’s cold lime softening technique, the temporary hardness of the water can be eliminated. This procedure, which uses slaked lime or calcium hydroxide instead of boiling, aims to transform the bicarbonate component into a matching carbonate compound. Lime is used in this softening process to combine with carbonic acid to form precipitates of insoluble carbonates.

2Ca (OH)2 + Mg(HCO3)2 → Mg(OH)2- + 2 CaCO3- +2H2O

Ca (OH)2 + Ca(HCO3)2 → 2H2O + 2CaCO3-

Removal of Permanent Hardness

  • Adding Washing Soda

As a salt of carbonic acid, washing soda is a chemical substance with the formula Na2CO3 known as sodium carbonate. It is a potent water softener and natural cleanser. It has a pH of 11, which is quite basic.

When washing soda is added to water that has a permanent hardness, the carbonate ions from the sodium carbonate react with the calcium and magnesium ions to create an insoluble product.

So, the following equation is displayed:


  • By Ion Exchange Resins

Using resins, this method finishes the water’s enduring hardness. Cl- and anion exchange resin are used to exchange Ca++/Mg++ ions and SO4-2 ions (RNH2OH). In this procedure, demineralization is achieved.

2RCOOH + Ca++ → (RCOO) 2Ca + 2H+

⇒ RNH2OH + Cl– → RNH2Cl + OH

⇒ H+ + OH → H2O


What are the main disadvantages of water hardness?


  • Water Hardness Disadvantages

1. Hard water should not be used for washing since it makes it hard to make soap lather.

2. In a reaction with soap, scum could form, wasting the soap.

3. The development of calcium and magnesium carbonates will cause tea kettles to furr.

4. Pipe blockages caused by hard water.


What are the major sources of water pollution?


Water Pollution

The pollution of water bodies is expressed as water pollution. Water pollution happens when industrial and agricultural effluents contaminate water bodies such as rivers, lakes, oceans, groundwater, and aquifers.

All lifeforms that are dependent on water, whether directly or indirectly, are affected when it is polluted. Years may pass before you notice the impacts of tainted water.

The poisoning of water bodies by dangerous chemicals is one of the root causes of water pollution. As it is evident from the aforementioned example, discarded plastic bottles, cans, and other garbage damage aquatic bodies. These lead to water pollution, which hurts the whole environment in addition to people. These pollutants release poisons that move up the food chain and finally reach humans. Most of the time, the results are only harmful to the local population and species, but they can have a worldwide impact.

1. Household Wastes

Water bodies receive tons of sewage waste. In addition to generating pollution, this also releases harmful germs that can cause disease.

Every day, rubbish is produced and dumped into the seas and oceans, even going as far as to create garbage islands. More than half of the levels of water pollution can be reduced by taking the simple action of merely throwing trash in the trash.

2. Industrial Wastes

Massive amounts of harmful substances, including lead and mercury, are released during many routine industrial processes. When humans regularly consume this contaminated product, it spread to other living animals. It also has an impact on water biodiversity.

Chemical runoff from irrigation, including fertilizers, insecticides, and other substances, enters water bodies. In a short amount of time, these pollutants pollute water bodies.


What are the 5 common waterborne diseases?


Waterborne Diseases

The term “waterborne diseases” refers to ailments that are brought on by pathogenic microorganisms that are spread through water and have negative effects on human health, such as sickness, death, or disabilities. These illnesses can be transferred on through bathing, washing, drinking polluted water, or consuming food.

  • Cholera

A bacterial disease called cholera is frequently transmitted by tainted water. The extreme diarrhea and dehydration brought on by cholera. Even in previously healthy persons, cholera can be lethal if ignored within a few hours. In modern nations, cholera has been all but finished thanks to modern sewage and water treatment.

  • Dysentery

Dysentery is an intestinal infection that causes in bloody or mucousy diarrhea. Dysentery can also cause uncomfortable stomach cramps. Having the flu or feeling sick (vomiting)

  • Jaundice

Hepatitis virus infection brought on drinking water consumption causes jaundice. When feces and regular drinking water are combined, the hepatitis virus multiplies readily and inflames the liver.

  • Hepatitis

Hepatitis E is a waterborne illness brought on by the Hepatitis E virus (HEV), and it spreads similarly to HAV through contaminated food and water. It is primarily present in places with low sanitation and insufficient basic hygiene standards.

  • Typhoid

Salmonella typhi bacteria, which cause typhoid fever, spread through polluted water. The patients often suffer extended fever bouts, appetite loss, nausea, headaches, constipation, and weight loss.

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