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What is chemistry?
Chemistry is the study of composition, structure and properties of various forms of matter and their transformation.
The study of many substances which nature has provided us and those which man has changed is simply the science of chemistry.
If we look at the things around us we will see almost everything connected with chemical industry.
Chemistry looks at:
Composition: What are substances made up of?
E.g. What makes common salt?
Changes: What happens when substances meet?
E.g. When a candle burns in air
Discoveries: How are new materials made?
Importance of chemistry
Quality is important in many industries as follows
A laboratory is a specialized room or building designed for doing experiments and keeping chemicals and apparatus.
It is a place for serious logical hardwork.
Qualities of a good chemistry laboratory
-It should have a large window to allow the circulation of air.
-Should be supplied with water systems.
-Should be supplied with electricity.
-It should not be slippery.
-It should contain enough chemicals.
-Should be well supplied with apparatus.
Accidents that are likely to occur in the laboratory
-Cut by broken glasses
-Inhaling toxic fume
-Never enter in the laboratory without permission from the teacher.
-Never run in the laboratory.
-Never start any experiment without any clear instruction from the teacher.
-Never touch chemicals and always read the signs of the chemicals whether it is toxic or flammable etc.
-Never use laboratory apparatus for keeping water.
-Never drink in the laboratory.
-Never eat in the laboratory.
-Always clean your bench after experiments.
Warning signs are signs drawn on the containers to give information to the user of chemicals.
The signs tell the user the nature of a certain chemical
e.g.corrosive, flammable, harmful etc.
Upon knowing the chemical warning signs, the user knows how to handle or to use the chemicals so that he can avoid accidents.
Petrol vapors catches fire easily. It should not be kept in the kitchen.
Mosquito spray should not be directed to flames, eyes, skin, nose, mouth.
Poisonous if inhaled and eaten so keep out of reach of children.
Poisonous if inhaled or taken in the body
It can catch fire and if put in the eyes is irritant.
Poisonous if inhaled or eaten.
Pesticides should not be very close to flames, eyes, nose, skin or mouth.
They burn your skin.
They burn your skin.
They burn your skin. Handle it with care of corrosive, flammable, harmful.
Chemical warning sign tells us about the dangers of any substance you handle at home or school.
The care and attention given to a victim prior to the arrival of professional medical help or before a victim is taken to the hospital.
Aims of first aid
-Establish no danger to casualty.
-Save one’s life.
-Prevent ones state worsening.
-To help one recover.
First aid kit
A container that contains chemicals and equipment for first aid.
Instruments and chemicals in first aid kit
Accidents and their remedy
– spit out once and wash the mouth with water.
– dilute by drinking much water followed by lime water or milk.
– dilute by drinking much water followed by vinegar, lemon or orange juice or solution of particular citric acid.
– remove the victim to the open air, if breathing has stopped apply artificial.
– wash immediately and thoroughly with a large quantity of water, then with sodium hydrogen carbonate and finally water.
– wash immediately with large volume of water then with acid then finally with water.
* Dilute acid- wash eyes separately with sodium hydrogen carbonate solution.
* Concentrated acid-wash with plenty of water then solution of sodium hydrogen carbonate.
– treat with iodine tincture and wrap bandage around it. Then seek professional medical help.
-wash the wound with water, wipe with damp cloth, and apply antiseptic cream.
These are methods of studying chemistry
– This involves of the use of sense organs e.g. eyes
– It involves looking at an event, fact as solution; ask how and why it occurs.
– The chemists use the available information to predict an explanation of the
– Hypothesis is a tentative answer to the problem.
– It is intelligent guess work.
– All predictions and guess work must be proved by experiments to be either true
– Chemists carry out experiments to test every hypothesis.
– The use of control explanation is very important.
– This involves collection of data obtained from experimentation.
– The data collected and preserved in essays, table, graph etc.
– After presenting the data, read and explain any trend shown by data.
Try to show what data means.
– It involves accepting or rejecting the hypothesis based on experimentation
– If hypothesis is proved false repeat experiment using hypothesis.
Most chemical reactions need heat so that they can process fast.
The common heat sources in lab include;
The Bunsen burner of Tenly is red because it is easy to handle and produce hot flames.
Flame– it is a burning fuel that produces light and heat.
Two types of flames;
-Produced when hole of Bunsen burner is closed.
-Not very hot
-It is bright
-Does not burn back
Non luminous flames
-Has three zones
-Can burn back
-Small and short
Non luminous flame is preferred because it is very hot and doesn’t produce smoke or soot.
Matter is anything that occupies space and has mass. Matter contains particles that are atoms, molecules.
Matter exists in three states
Solid- Brick, block of ice, wall.
Liquid- Water, soda, tea.
Gas- Oxygen, nitrogen, carbondioxide.
Element: Is a single pure substance that cannot be broken down into simpler substances by any chemical means.
An element contains one type of atom.
Atom: Is the smallest particle of an element which can participate in a chemical reaction.
The atom of an element has all the properties of that element.
The building block of matter is atom.
Molecule- Occurs when two or more nonmetal atoms come together.
Solid- Aluminum, copper, uranium.
Liquid- Mercury, bromine.
Gas- Hydrogen, nitrogen, oxygen.
Elements can be metals or nonmetals.
Metals- Lead, copper, gold, zinc.
Nonmetals- Fluorine, chlorine, neon, oxygen.
Properties of metals:
Kinetic nature of matter
->In solid state, free movement of particles is not allowed, only vibration is allowed. This is because of a strong force of attraction existing between molecules or atoms or irons.
->So when heat is applied, particles vibrate in fixed position.
->In liquid state, there is a movement of particles but not as free as in gas state.
– Still there is a weak force of attraction.
->In gas state there is free movement of particles.
– Particles move in all direction as no force of attraction.
Mixture and compound
Mixture is a substance formed by two or more elements or compound at both which are in physical combination.
->The components of a mixture are not chemically combined.
->The components making a mixture can be separated by physical method.
e.g. evaporation, titration, distillation, magnetism etc.
Types of mixtures
-Is a mixture in which the contents can’t be seen.
-e.g. sugar dissolved in water to get sugar solution.
The sugar and water have mixed together.
-Salt dissolved in water
The two mix to form salt solution.
-A mixture in which the individual components can be easily distinguished.
-You can see the contents making the mixture.
E.g. Chalk powder in water, sand mixed with water, oil mixed with water.
-In all these examples the contents can be seen easily.
Is a substance formed by two or more elements chemically combined together.
->The individual components of the compound cannot be separated by physical method.
Examples of compound
– Common salt
It has sodium atom and chloride atoms chemically combined.
– Copper sulphate
Has copper atom, sulphur and oxygen atom in chemical combination.
– Is a mixture of two or more substances.
– Is a homogeneous mixture of two or more substances.
– Is a mixture of solute and solvent.
That is solution=Solute+Solvent
Is a substance which dissolves in a solvent.
E.g. sugar, salt.
Is a substance that dissolves a solute.
Examples of solutions.
-Alcohol and water
-Salt and water
-Iodine and water
Classification of solution based on solvent solute ratio.
There are 3 categories;
– The one that contains less solute then it can dissolve.
– The one in which more solute can dissolve at a given temperature.
– The one which has enough solute, no more solute can dissolve at the same temperature.
E.g. you shake some sugar in water it will dissolve and if you add more it will remain undissolved until it is heated.
Is a solution which contains more solute than it can hold at the same temperature.
It can be made by heating the solution and solute until it is saturated.
Classification based three states of matter.
Two or more solutes mixed together
->Brass- solution of zinc and copper.
->Bronze- solution of tin and copper.
->Steel- solution of phosphorous, sulphur, nickel, carbon, iron.
*Liquid solution E.g. Salt and water
*Gaseous solution-Two or more gases mixed together.E.g. air
Is a liquid containing solid particles spread throughout it and which settle at the bottom on standing.
Suspension are heterogeneous mixtures.
Suspensions in real life
Many medicines are suspensions especially those containing the label “shake before use”
Examples of suspension;
-Paint pigment in oil
-Porridge; suspension of flour in water
-Mist; suspensions of water particles in air
METHODS OF SEPARATING MIXTURES
Decantation is the process of slowly pouring out the liquid in a clean beaker and leaving out behind the sediment’s eg.muddy, water
Application-Making tea or coffee you can separate tea/coffee by this process
Decantation involves two steps
Filtration is the process of removing suspended particles from a liquid by allowing the liquid to pass through a porous material such as filter paper and leaving the solid behind the filter paper.
The liquid that passes through the filter paper is called filtrate.
The solid that remains on the filter paper is called residue.
Application-Filtering drinking water
*Evaporation is the process of obtaining solid solute by leaving solvent.
Separation of salt from salt solution
Separation of sugar from sugar solution
Bunsen flame, tripod stand, wire gauze, water bath that is a beaker and evaporation basin.
Place the wire gauze on top of tripod stand takes a beaker with some water and places the wire gauze and place the evaporating basin on top of the containing water. Heals the water in a beaker to form steam which in turn boils the solution on the basin. The water will evaporate, the solid crystals will remain.
Separation of salt from sea water.
Is the process of boiling liquid to form vapor and then cooling the vapor to obtain liquid. The process is applicable to get pure solvent and solute from a solution.
-Solute will remain in a distilling flask and solvent is collected in the beaker.
Aim- To obtain pure water from copper sulphate solution.
– It boils and steam rises into condenser.
– The salt is left behind.
This method can also be used to obtain pure water from sea water.
Note: During distillation, evaporation and condensation take place at the same time but at different parts of the apparatus. The pure liquid is collected is called distillation.
It is used to separate two immiscible liquids. For example the mixture of oil and water, the oil floats to the top, while water is at the bottom.
When the top is opened, the water runs out. The top is closed again when all the water has gone. Their separation is based on differences in their densities.
It is the process where by a substance changes from solid to gas.
If a mixture of ammonium chloride and sodium chloride is heated, the ammonium chloride turns directly to vapor but the sodium chloride remains. When the vapor is cooled, solid ammonium chloride collects to leave sodium chloride.
Is the method used to separate a mixture of colors.
E.g. It separates a colored substance from black ink.
The components separate by passing through a medium.
The components move at different rates over a material such a filter paper.
Is which the method used to separate mixture of two solvents which differ in boiling points.
E.g. a mixture of alcohol and water.
Petroleum can be spilt up into various products like petrol, diesel, and kerosene by fractional distillation
Separating mixture of air.
Separation of alcohol from water.
Alcohol boils at 780C and water boils at 1000C.
By using thermometer, temperature can be regulated to allow only alcohol to boil and form to vapor before water.
Therefore alcohol is collected before water.
CHANGES OF STATES OF MATTER
Matter is anything that has mass and occupies space.
Matter exists in three states namely solid, liquid, and gas.
Some substances can exist in all three states of matter.
E.g. water-Temperature below 00C to ice-solid
-Temperature above 00C to water-liquid
-Temperature above 1000C the liquid boiled to vapor -gas.
NOTE: Change in state of matter is due to the changes in heat energy.
(Solid) heat ice (liquid)
(Liquid) heat (gas)
(Liquid) freeze (solid)
INTERCONNVENTION OF STATES OF MATTER
-Melting: Is the process whereby solid changes to liquid.
-Freezing: Is the process whereby liquid changes to solid.
-Evaporation: Is the process whereby liquid changes to gas
-Condensation: Is the process whereby gas changes to liquid.
-Sublimation: Is the process whereby solid changes to gas.
PHYSICAL AND CHEMICAL CHANGES
Is the change in which no new substance is formed.
-melting of ice
-melting of wax
-magnetization of iron
-process of evaporation, condensation, freezing, melting
-breaking of glass
-tearing of pieces of paper
-melting of iron
-heating of wire
-dissolving salt in water
Is the change in which a new substance is formed.
-burning of kerosene
-burning of candle
-burning of magnesium metal
-burning of wood
-rusting of iron
Rust is a reddish brown substance which forms on the surface of iron or steel.
If the process is not stopped, rusting may destroy the whole structure made of iron or steel.
Eg. Rusting of bridges, rusting of machines, rusted iron sheets on roofs, containers, rails etc.
Conditions favoring rusting
Rusting occurs only when both oxygen and moisture are present.
Iron reacts with oxygen of the air to form reddish brown oxide.
Iron+ oxygen—->iron oxide
Fe + O2——->Fe2O3
At the same time, the iron oxide combines with water to form hydrated iron oxide (rust)
Iron oxide+ water—->rust
Fe2O3 + H2O—->Fe2O3 .X H2O (Rust)
Aim: to find the conditions needed for iron to rust.
Apparatus: test tube, nails, test tube racks, sand paper.
Cover the mouth of the test tube with dry cotton wool.
Pour this water into tube Y, until the nails are submerged.
Pour oil on top of the water.
Pour this oil in test tube Z until the nails are submerged.
How can we prevent rusting?
To stop iron and steel from rusting we must protect them from water and oxygen. The most important way of doing this are:
An oil base paint is applied on the surface of an object etc.
The layer of point keeps oxygen and water away.
Moving parts should not be painted. The layer of point will be easily scratched off. Instead they are oiled or greased. The grease also helps lubrication.
Alloying is a mixing up of different metals. What results in an alloy. Stainless steel is an alloy which does not form rust.
Stainless steel contains chromium, nickel and manganese mixed with iron.
Iron and steel may be covered with a layer of more reactive metals.
E.g. buckets and dustbins are coated with zinc. This process of coating metals by zinc is called galvanization.
Tin cans are made of steel but coated with thin layer of tin to protect the steel.
Is the joining of more reactive metals with iron or steel, where the metals undergo rusting instead of iron.
The process is known as sacrificial protection.
This method is used to protect large structures such as bridges, ships and pipelines from rusting.
AIR COMBUSTION AND FIRE FIGHTING
Is a colorless mixture of gases. It is colorless and tasteless.
The atmosphere which covers the earth is made up of air.
More air is near earth’s surface than away from it.
COMPOSITION OF AIR
Air is composed to several gases such as: nitrogen, oxygen, carbon dioxide, water vapor and noble gases.
|GAS||% BY VOLUME||BOILING POINT|
The percentage of water vapour varies from place to place and is not included in the table. Air may sometimes contain traces of impurities such as C02, Sulphur dioxide, H2S and other gases.
Air pollution is caused by these gases and other gases.
Separation of air into its constituent gases
Main stages in the process of liquification of air:
By cooling the air to very low temperature, ice and solid carbon dioxide are removed.
At – 2000C only helium and neon remain as gases.
These cold gases are used to cool the compressed air.
The liquid is subjected to fractional distillation.
Nitrogen boils off first because it has a lower boiling point- 1960C followed by oxygen which is – 183oC
Is air a mixture or a compound?
To answer this question, we must give some evidences.
-The composition of air does not correspond to any simple chemical formula.
Any compound must have a specific formula.
-The composition of air varies slightly in different localities at different times.
-No energy change when the constituents of the air are mixed.
-The components in air can be separated physically.
-The gases in air are not chemically combined.
USES OF THE GASES IN AIR
This gas is present in air in the largest percentage. It is not directly available to plants and animals. It is not essential for breathing although its presence in air helps to dilute oxygen. Nitrogen in plants is obtained by indirect methods e.g. nitrogenification.
All plants and animals need oxygen for breathing.
Aquatic animals use oxygen dissolved in water.
Oxygen is necessary for burning of fuel and rusting.
Note: green plants supply oxygen to the air during photosynthesis
Respiration in plants and animals produces it.
All fires from burning fuel produce it.
Green plants take it from the atmosphere.
It is used in fire extinguishers.
Is the lightest gas known. It has replaced hydrogen.
Used for filling balloons and also used to fill certain photographic flash bulbs.
Is used for filling electric bulbs. It is the cheapest and most abundant of the noble gases. If air is used instead, the filament may burn off.
Is used for filling electric discharge tubes for illuminating and for advertising signs.
Is a chemical change in which heat is given out & sometimes light.
In this process one or more of the resistant is gas.
When things burn in air, they combine with oxygen and give out hot gases.
These are usually seen as flames.
Most substances that burn contain carbon and hydrogen. I.e. the burning of organic substances produces carbon dioxide and water vapor.
If oxygen supply is not enough, combustion is incomplete and carbonmonoxide is produced.
Advantages of combustion
-Burning of fuel produces heat.
Is a method directed at limiting the spread of fire and extinguish it.
It causes a lot of property destruction such as:
-May burn one to death
-May burn buildings
The most dangerous fires are caused by explosions.
Causes of fire
How to prevent fire?
-Extinguish all glowing residues before disposal.
-Use the fuel which is meant for a particular burner.
-Cool burner before refilling it with fuel.
-All flammable chemicals should be kept out of lab.
-Never heat flammable substances with direct flames.
-Never pour flammable substances in the sink.
How to control fire?
A fire will start or continue to burn if three factors are satisfied.
You can extinguish the fire by removing the combustible material.
Extinguish the fire by blocking air as oxygen supply to the fire.
Extinguish by lowering the temperature below the kindling point.
HOW TO CLASSIFY FIRES
Classification depends on what is actually burning.
You need to know the type of fire before you start fighting it
The burning of material is either wood, coal, paper, rubber, plastics, clothes or furniture etc.
*Water is the best extinguisher of these fires.
If water is not available use any other type of fire extinguisher.
The burning material is flammable liquid eg.petrol, ether, kerosene, alcohol etc.
*To extinguish use a fire blanket or sand if the fire is small, if large use carbondioxide extinguishers.
The burning material is liquefied gas. E.g. hydrogen or coal gas.
*Foam and carbondioxide extinguishers are the best.
The burning material is a metal e.g. sodium and potassium which catch fire on exposure to water or oxygen.
*Extinguish by C02 extinguisher.
These are fires on electrical equipment’s.
*You must first find the main switch and put it off
Then use C02 extinguisher to put it off.
Never use water on electric fires because water increases electrical conductivity.
It is one of the gases which occurs freely in the atmosphere.
It is the second abundant gas in the atmosphere having 21% by volume.
It also occurs in combined states in form of salts, water, silicates oxides of metals and nonmetals. Oxygen is released in the atmosphere by a food making process called PHOTOSYNTHESIS.
Lab preparation of oxygen
It can be prepared using:
-hydrogen peroxide ( H2O2)
-Potassium chlorate (KClO3)
Preparation of oxygen using hydrogen peroxide
Is the main method of preparing oxygen in lab by allowing hydrogen peroxide to come into contact with manganese (IV) oxide which is a catalyst.
Hydrogen peroxide is an unstable compound which decomposes to give oxygen and water even at room temperature. However the reaction is slow, so it is speeded by a catalyst.
Put manganese oxide in a flask as a catalyst.
Arrange the apparatus as shown in the diagram.
Add drop by of hydrogen peroxide to it.
Manganese (IV) oxide catalyses that decomposition of hydrogen peroxide to give off oxygen.
Hydrogen peroxide magnese (IV) oxide>water+oxygen
2H2O2 Mn O4 >2H2O +O2
Oxygen is collected by downward displacement of water because it is less dense than water.
Since oxygen is collected over water it is not dry, to dry it a desiccant called “silica gel” is used.
Is a substance which changes the rate of chemical reaction but itself remains unchanged at the end of the reaction.
Types of catalyst
It increases the rate of chemical reaction.
Decreases the rate of chemical reaction.
PROPERTIES OF OXYGEN (O2)
-It is colorless and tasteless gas.
-It’s density is approximately the same as that of air.
-It is neutral to litmus paper.
-It is slightly soluble in water.
-It supports combustion.
-Metal burns in oxygen to form basic oxides (i.e. MgO, CaO)
E.g. Action with magnesium.
It burns with a bright light to form white ashes of MgO.
Magnesium + Oxygen——->magnesium oxide
Mg(s) + O2(g)————>MgO(s)
-Many non-metals burn in oxygen to form (acidic oxide)
eg.CO2, sulphurdioxide etc.
Action with sulphur:
It burns with a bright flame with pungent smell forming sulphurdioxide gas.
ie.Sulphur+ Oxygen ——->Sulphurdioxide
S(s) + O2(g)———>SO2
Classification of oxides:
Oxides are classified according to the chemical properties:
These are oxides of nonmetals which dissolve in water to form acids.
eg.CO2, SO2, P2O2
Are oxides of metals which dissolve in water to form bases (alkalis)
eg.MgO, Na2O, CaO, K2O etc.
Are oxides which have both acidic and basic properties:
Examples: aluminum oxides Al2O3
Zinc oxide ZnO
Lead oxide PbO
Test for oxygen
Oxygen re-lights a glowing wooden splint.
This is the best test of oxygen.
USES OF OXYGEN
Example in high altitude flying or climbing and also when anesthetics are administered to a patient.
Hydrogen gas does not occur free in nature.
It is found as part of chemical compound such as water, petroleum, protein, fats and carbohydrates.
Lab preparation of hydrogen:
It can be prepared in the lab by the action of reactive metals as dilute acids.
The common metal is zinc and acid is dilute hydrochloric acid or dilute sulphuric acid.
-Set the apparatus as shown.
-Put zinc granules in a bottom flask.
-Pour dilute acid through the funnel, the funnel should almost touch the bottom of the flask.
Dilute hydrochloric acid reacts with zinc and give off a gas which is hydrogen.
If the reaction is slow copper sulphate is added to speed up the reaction.
Zinc+ dilute hydrochloric acid—->zinc chloride+ hydrogen
Zn(s) + HCL(aq)—–>ZnCL2(aq) + H2(g)
Zinc + dilute sulphuric acid ——>zincsulphate +hydrogen
Zn(s) +H2SO4(aq) ——->ZnSO4(aq)+ H2(g)
Hydrogen is also collected by downward displacement of water since it is less dense than water and air.
PROPERTIES OF HYDROGEN
-Colorless, tasteless, and odorless
-Less denser than air
-Slightly soluble in water
-Neutral to litmus
Hydrogen does not support combustion.
It burns with a blue flame in air forming water.
Hydrogen + oxygen ——>water
This mixture explodes with a pop sound forming water.
This is the best for hydrogen gas.
Hydrogen changes heated copper oxide, lead oxide, and iron oxide to metal.
Copperoxide + hydrogen ——–>copper +water
CuO+ H2 ————->Cu + H2O
Aim: investigate the effect of hydrogen on copper (II) oxide
USES OF HYDROGEN
-The chief use of hydrogen is as fuel. It burns and gives out much heat.
-Is used to manufacture ammonia. This process is known as Haber process.
Nitrogen + hydrogen———->ammonia
-Hydrogen is used in balloons and airships.
-Is used in the manufacture of organic chemicals such as nylon and methanol.
-Is used in making fats.
Oil combines with hydrogen to form solid fats. This process is known as hydrogenation or hardening of oil.
OCCURANCE AND NATURAL SOURCE OF WATER
Water is the commonest substance on earth.
It covers about 4/5 of the earth’s surface.
Water is essential to life as every living thing depends on it.
The human body is 67% water by mass, animals and plants can be found either in water or in areas where it can be found.
Natural sources of water:
Water is found in all three states.
Ice is the solid form, steam or vapor is the gaseous form.
Water circulates around the earth in a process known as water cycle.
The sun provides the driving face for the water cycle.
During the day, the sun evaporates water from different sources.
This causes the amount of water vapor to float on the air.
In the outer upper parts of the atmosphere, the vapor condenses to form clouds.
The clouds are drifted by wind and form heavy clouds.
Further cooling of these heavy clouds result in rainfall.
The rain water soaks into the soil.
The rest of the rain water runs on land to join rivers and finally the seas and oceans.
Then the whole cycle begins again.
Substances in water:
-Natural water is never pure.
-It contains different substances dissolved in it.
-Rain water contains dissolved gases.
-If the gases are acidic e.g.SO2, CO2, or NO2, we may have acid rain.
-River water contains dissolved and suspended solids.
-As rivers approach the ocean, it forms a delta, much of mud and large solids are deposited in the delta.
-The sea water contains about 3.6% by mass dissolved solids.
-These include chlorides of sodium, potassium, magnesium and calcium, 3/4 of ocean salts is sodium chloride.
Physical properties of water
-It is colorless, odorless and tasteless.
-In its pure state it is transparent.
-Pure water is neutral.
-At atmosphere pressure, pure water boils at 100oC and freezes at 0oC.
-It is a very good solvent.
-It expands when it freezes.
-Water is used as standard. It is standard for determining specific gravity of substances.
-Any substance with a specific gravity less than that of water will float on water.
-Water has a high specific heat capacity.
Chemical properties of water
Water is a very stable compound, does not decompose easily by heating.
It decomposes slightly at 2500oC and completely at 5000oC
Test for water
The two main methods are:
-Water reacts and changes the white powder of anhydrous copper (II) sulphate to blue.
Anhydrous copper (II) sulphate + water ——>hydrous copper sulphate (blue)
-Water turns blue cobalt chloride paper to pink.
-Reaction of water with metals .Active metals such as potassium and sodium react with cold water very violently to produce hydrogen.
Potassium + water——–àpotassium hydroxide + hydrogen
K+ H2O ————àKOH +H2
Sodium + water ——>sodium hydroxide + hydrogen
Na + H2O———>NaOH + H2
Magnesium does not react with cold water, only with steam.
Magnesium +steam ——-> magnesium oxide + hydrogen
Mg+H2O ———-> MgO + H2
Reaction of water with oxides
The oxides of potassium, sodium and calcium react with water to form hydroxides.
Potassium oxide + water ——–>potassium hydroxide
K2O + H20————->KOH
Oxides of non-metals such as sulphur, carbon and phosphorus form acids.
ie.carbondioxide + water ——–>carbonic acid
C02 + H2O ———–>H2C03
Sulphurtrioxide + water ———->sulphuric acid
SO3 + H20 —————> H2SO4
Phosphorous pentoxide +water ———>phosphoric acid
P205+H2O ————->H3 PO4
WATER TREATMENT AND PURIFICATION
The water supplied to town is often taken from rivers, lakes etc. which in most cases are quite polluted. So they need treatment in order to make it safe to drink etc.
Steps in purification of water
The water is filtered by sand and gravel of the shore before it enters on infiltration well. This removes parts of organic pollutants, viruses and bacteria.
The water is allowed to stand in large settling banks where solid particles and mud settle at the bottom.
Aluminum sulphate (AI2(SO4)3.16 H2O) and shaked lime Ca(OH)2 are added to precipitate the suspended clay matter.
The two chemicals react to form aluminum hydroxide and calcium sulphate.
AL2(S04)3 + 3Ca (OH)2
2AL(OH)3(S) + 3CaSO4
The aluminum hydroxide is bulky and sticky that carries down with it most of the suspended material and bacteria.