Properties of natural resources - class-IX

The specific heat of water is $1$ $calorie/gm^oC=4.186$ $Joule/gm^oC$, which is higher than another common substance.

The density of water is $1 g/cm^{3}$. Density is a ratio of Mass to the Volume. 1 meter long, 1 meter wide, 1 meter high storage tank can store 1,000 kg mass of water. So the density of water is 1. Therefore 1 kg water= 1 litre water(approximately).

Pure water is tasteless. As it does not have any impurities(minerals, salts). So, the above statement pure water has a pleasant taste is false.

Pure water has maximum density at $4^oC$ when water is heated from $0^oC$ its volume decrease because its density increases and we can see this effect up to $4^oC$.

The boiling point of water is not proportional to the atmospheric pressure. As the elevation increases, atmosphere decreases because air is less dense at high altitudes. Because the atmospheric pressure is lower, the vapour pressure of the liquid needs to be lower to reach boiling point. Therefore, less heat is required to make the vapour pressure equal to the atmospheric pressure.

The density of water at $0^oC$ is less than the density of water at $4^oC$. When water is heated from $0^oC$ its volume decreases because its density increase we can see this effect up to $4^oC$, afterward density decreases.

Ice floats over water as its density is about $9%$ less dense than liquid. The orientation of hydrogen bonds causes molecules to push further apart which lowers its density (cage like structure).

The water pipes burst in cold countries in winter due to anomalous expansion of water. In cold countries, when temperature falls below $0^{\circ}$C, aquatic life can survive due to anomalous expansion of water. When the temperature of surrounding reaches upto $4^{\circ}$C, the upper surface of the pond will have maximum density and so it sinks to the bottom of the pond.

Pure water or distilled water does not conduct electricity. In distilled water there are no impurities, there are no ions, there are only neutral (no charge) water molecules and these neutral molecules do not have charge, So, distilled water does not conduct electricity.

The property of water make it easy to contaminate and difficult to purify is its tendency to dissolve a large number of substances. The ocean/sea water is not fit for drinking and washing because it contains high concentration of the dissolved salts.

Water can dissolve a wide variety of substances the is why water is known as universal solvent. Plant use this property of water for taking minerals from the soil.

Pure water has maximum density at $4^oC$. When we heat water from $0^oC$, its density increases up to $4^oC$ then density decreases. (Anomalous expansion of water)

Water has high specific heat capacity. The other options are physical properties of water.

Distilled water is purified water free of all dissolved salts. River, well and rain water is water in free state as collected in nature.

The atomic masses of O and H are 16 g/mol and 1 g/mol respectively.
The molecular formula of water is $H _2O$ and its molecular weight $2(1) + 16=18$ g/mol.
Note:
Water is one of the most precious resources on earth and is necessary for all living beings. We use water for different purposes like drinking, cooking, bathing, washing and many more activities. Pure water is colorless, odorless and tasteless.

At $4^oC$ the density of water is maximum and volume of water is minimum.

When water is heated from $0^oC$ its value decreases because its density increases and we can see this effect up to $4^oC$ because the density of ice is maximum at $4^oC$. Afterward the density decreases, the volume increases.

At 0$ ^{\circ}C $, water exists as ice. 

Water exhibits anomalous expansion; it contracts as it cools until it reaches 4 degrees Celsius, after which it begins to expand as it cools further toward freezing. Therefore, its density is highest at 4 degrees Celsius.

Water acts as a powerful ionizing agent due to its high dielectric constant. Water has high polarity and forms hydrogen bonds.

Water is cooled from $4^{\circ}C$ to $0^{\circ}C$. It is called "Anomalous expansion of water", i.e. The expansion between 4 and 0 is due to the formation of larger clusters in the water molecules.
When water molecules go from $4^{\circ}C$ to $0^{\circ}C$, they are forming groups in small lattices, what increases volume and decreases density. When water ices, then all their molecules are forming that lattice, as mineral crystals do, with the volume expanded.
Above $4^{\circ}C$, thermal expansion sets as thermal vibrations of the OH bonds of water becomes more vigorous, tending to shove the molecules farther apart and water expands.
As a result of this water at $4^{\circ}C$ is denser than that at $0^{\circ}C$. This causes floating of ice on water during winter. Bursting of pipes is also due to anomalous expansion.
Thus, Option B is correct.

Water boils at 100$^o$ while paper burns at 200$^o$. Thus water can be boiled in paper.

Water is not a mixture but a compound. It has elements hydrogen and oxygen which are combined chemically with two hydrogen and one oxygen atoms. These cannot be separated by any physical means.

Pure water is a bad conductor of electricity. This is because free electrons are not present in pure water which allow the flow of electricity. Pure water is a bad conductor of electricity.

Water in pure form is a bad conductor of electricity because of the absence of free electrons (salts and minerals) that allow the flow of electricity.

Salt and sugar are soluble in water and form solution with water. Oxygen is also water soluble because the aquatic animals are able to breathe because oxygen is present in the dissolved form. As temperature increases solubility decreases, that's why in Eutrophication there is high BOD.(Biological Oxygen Demand)

When we heat water, we can find bubbles coming from it. This is because the solubility of gases decreases as the temperature increases and that is why the dissolved air bubbles go out from the water. Then as the boiling point of the water is reached ($100^{\circ}C$), water vapour starts to form inside the liquid in the form of bubbles.  

Pure water is bad conductor of electricity due to lack of impurities (salts and minerals).

Pure water, also known as purified water, is water from a source that has removed all impurities. Distilled water is the most common form of pure water. The water can be purified by carbon filtration, microporous filtration and ultraviolet oxidation. Some places use a combination of purification processes. Pure water is colorless, odorless and transparent.

Water pipes burst because the water inside them expands as it gets close to freezing point and this causes an increase in pressure inside the pipe. When pressure gets too high for the pipe to contain it ruptures.

Water exists in solid state (ice), liquid state (water) and gaseous state (steam or water vapours).
Water is the only substance that exists on earth in all the three physical states: solid, liquid and gas. Earth has rivers, lakes and oceans in liquid form. 

Water is  a universal solvent.  Water is capable of dissolving a variety of different substances. It dissolves more substances than any other liquid. Water is important to every living thing on earth. Wherever water goes, either through the ground or through our bodies, it takes along valuable chemicals, minerals, and nutrients.

Water is neutral in nature.
Since pH is defined as the negative log of the hydrogen ion concentration, the pH of pure water is 7 or neutral. Pure water is neutral because the number of positive hydrogen ions produced is equal to the number of negative hydroxide ions.

$H _{2} O$ at 4$ ^{\circ}C $ has maximum density. Ondecreasing the temperature from 4$ ^{\circ}C $ to 0$ ^{\circ}C $, its density decreases. Ice has 0$ ^{\circ}C $ has also less density compared to water at 4$ ^{\circ}C $. So, ice floats on water. 

True bbecause, it doesn't contain any ions, salts or impurities, which are necessary for conduction of electricity.

The ratio of hydrogen to oxygen in water is 2:1.
Two molecules of the diatomic hydrogen gas, combine with one molecule of the diatomic oxygen gas to produce two molecules of water. In other words the ratio of hydrogen to oxygen is 2:1, the ratio of hydrogen to water is 1:1, and the ratio of oxygen to water is 1:2.
$2H _2 + O _2 \rightarrow 2H _2O$

When water gets converted into ice, its volume increases. 

By boiling, water can be purified in a simple way as the nonvolatile impurities remain back and pure water is condensed separately.

Sand $(SiO _2)$ is not soluble in water.

Water is a good solvent. It combine with dirt and other particles with it when treated with soap, which is water soluble and form lather in water. Hence due to its solubility it is used while washing clothes. 

Pressure changes inversely with altitudes and boiling point directly proportional to pressure. Pressure and boiling points are low at high altitudes. So water boils below 100$ ^{\circ}C $.

Temporary hardness is caused due to the presence of carbonates of calcium and magnesium which can be removed by boiling the water.

Temporary hardness causes due to the presence of carbonates and bicarbonate ans permanent hardness is caused due to the presence of chlorides and sulphates.

Option (C) is correct.
Boiling and freezing temperatures of water were used to define a temperature scale.The scaling of zero degree centigrade is based on this fact.

Water is known as the universal solvent because it is capable of dissolving a variety different substances, which is why it is such a good solvent.

Density of water is maximum at $4^{\circ}C$. 

Water exists in three states namely solid, liquid and gas in the form of ice, water and vapour.

Evaporation is an endothermic process because water molecules must absorb heat from the surroundings to increase their kinetic energy. For example, sweat which cools the human body as it evaporates from the skin.

The density of ice is less than the density of water i.e., $1$ $g/cm^3$ due to its cage like structure of hydrogen bonds. The orientation of hydrogen bonds cause the molecules to push further apart which lowers its density. 

Statement 1: Ice is less dense than liquid water.
Hence, an ice cube floats in a glass of water.
Statement 2: Water molecules are polar due to electronegativity difference between O and H atoms and non linear structure of water molecule.
Hence, statement 1 is correct but statement 2 is not correct.

Melting is endothermic. Melting process needs energy to convert it from solid to liquid state.

Water possesses intermolecular hydrogen bonding in the condensed phase rather than intramolecular hydrogen bonding. Therefore statement (D) is incorrect