chemicals in our daily life ii science

Ptd By:Raghavendra D R

You know that, water is one of the mostabundant and important compound in the world. It isthe major constituent of all living organisms. Someplants contain more percentage of water. The humanbody has about 65% of water. Neither plants, animalsnor human beings can survive without water.

Water is made up of hydrogen and oxygen. Onemolecule of water contain two atoms of hydrogen andone atom of water which are chemically combined.

From time immemorial, water been the drivingforce of every civilization and people attached greatimportance to an adequate supply of water for different,purpose like agriculture, cooking, drinking, washing, etc.

In ayurveda water has been given an importantplace. Water is used to treat common problems. It iscalled hydrotherapy.

Traditional methods of obtaining potable waterinclude the following. Boiling, making sunlight fall onwater, adding tulsi leaves, camphor, dropping red hotiron balls.

There are methods of removal of colour, odour,suspended matter and microbes from the water. Alsothere are methods of removal of hardness. Watertreatments include stages of coagulation orsedimentation, filtration, decolourisation andsterilisation. Alum is used for sedimentation. Some ofthese practices have been used in ancient civilizationalso.

You know that chemical formula of water isH2O. In a water molecule one atom of oxygen isbound to two atoms of hydrogen as shown in fig.

Water is called the “Universal Solvent” because it dissolves more substance than any other solvents.

we store water in different metallic containers.We also boil water in metallic containers. Does waterreact with the metallic container?

Metals like copper, aluminum and tin show noaction with water at ordinary temperature.

Many metals and their alloys are used toprepare utensils, buckets, kitchenware and otherarticles, because they do not react with water undernormal conditions.

Sodium and potassium are soft metals and can becut with a knife. They react with water, forming theirrespective hydroxide liberating hydrogen gas.

Note:

Sodium is to be kept under kerosene as it canreact with oxygen and water vapours present in air. Themetal should always be handled with a pair of tongsbecause it can even react with moisture on the hand andcause blisters. Kerosene has no affinity towards sodium.

Metals like sodium, potassium react with cold water forming respective hydroxides liberating hydrogen gas.

(Sodium Hydroxide)

Other metals also react with water at different conditions.

(Calcium Hydroxide)

(Magnesium hydroxide)

• Room Temperature

• Boiling water

When steam is passed over red hot metals like zinc, iron, magnesium we get respective oxides and hydrogen gas.

1. When steam is passed over red hot coke, Mixture of carbon monoxide and hydrogen is formed.

• As an industrial fuel.

• Used in the manufacture of hydrogen

2. When steam is passed over red hot silicon,which is a non metal, silicon dioxide andhydrogen gas are formed.

Generally when a non metallic oxide dissolves in water, acid is formed.

Carbonic acid is present in soft drinks.

When nitrogen dioxide, and sulphur dioxidepresent in the atmosphere of certain industrialregions, dissolve in rain water, they cause acid rain.

When calcium oxide reacts with water it formscalcium hydroxide.

you might have seen this reaction when a paste forwhite washing is being prepared.

There are many substances which absorbmoisture such as magnesium chloride, solid sodiumhydroxide, solid potassium hydroxide, anhydrouscalcium chloride, calcium nitrate and Ferric chloride.

Certain water-soluble substances, whenexposed to the atmosphere at ordinary temperature,absorb moisture from the atmospheric air to becomemoist and ultimately dissolve in the absorbed water.Such substances are called deliquescent substancesand the phenomenon is called deliquescence.

Certain hydrates lose water when exposed to airof moderate humidity. An example is sodium sulphate

. The loss of water from hydratedcompounds to the surroundings is calledefflorescence. Commonly used washing soda isanother example for efflorescent substance.

Water is a very common and suitable solvent.Some impurities dissolve in it very easily. Mostlysoluble salts of Calcium and magnesium make waterhard. As the percentage of calcium and magnesiumincreases in water, the degree of hardness alsoincreases.

Hard water does not produce much lather withsoap. Generally water from regions having limestoneand other mineral rocks is hard water. Calcium andmagnesium bicarbonates, sulphates and chlorides ingeneral cause hardness in water.

The salts causing hardness are water soluble.Calcium carbonate does not cause hardness because itis insoluble in water.

Soft water produces a rich lather with soap.Rain water and spring water are examples of softwater, since they contain small amount of dissolvedsalts in them.

Hardness of water can be removed by twomethods:-

• If hard water contains Calcium and Magnesiumbicarbonates, it can be made soft by boiling.

In this reaction, Calcium bicarbonate decomposesto insoluble calcium carbonate and carbondioxide.

Example :

• Hardness can be removed by the addition ofwashing soda to water. In thisreaction, the soluble salts of calcium andmagnesium are converted into insolublecarbonates. The soluble sodium salts do not causehardness.

Water, so obtained is soft water. But it is unfitfor drinking as it contains excess of washing soda andexcess of sodium salts.

Desalinisation is an artificial process by whichsaline water ( generally sea water) is converted in tofresh water. It is suitable for human consumption.Sometimes the process produces table salt as a by-product. This method was invented during secondworld war.

So Dear Students today you have studied aboutchemical properties of water, purification of water, actionof water on metals and non-metals, reaction of water withmetallic and non-metallic oxides. You have also studiedabout deliquescent substances, efflorescent substancesand about hard water and soft water. The methods ofremoval of hardness of water. In addition to that you havestudied about Desalanisation i.e., conversation of seawater into fresh water.