Chapter 5 water and solution

Chapter 5Water and Solution

Water is the most abundant substance on earth.

Like any other substances, water has its ownunique characteristics.

A. Physical Characteristics of Water

1. Water can exist in three states:

a. Solid b. Liquid c. Gas

5.1 Physical Characteristics of Water

2. At room temperature, pure water is a

a. colourless,

b. odourless and

c. tasteless.

5.1 Physical Characteristics of Water

liquid solid

Freezing point of water is the temperature atwhich water freezes into ice.

5.1 Physical Characteristics of Water

Freezing Point of Water

1.Water changes from liquid to solid at its freezingpoint.

2. The freezing point of pure water is 0 oC.

3. The temperature remains constant at 0 oC until waterfreezes completely.

5.1 Physical Characteristics of Water

When the temperature drops, the waterparticles move slower.

Therefore, the forces of attraction among theparticles grow stronger.

At 0 oC, the forces of attraction are so greatthat the water particles are held in fixed

positions.

Waterfreezes into ice!

5.1 Physical Characteristics of Water

liquid gases

Boiling point of water is the temperature atwhich water boils and becomes steam.

5.1 Physical Characteristics of Water

Boiling Point of Water

1. Water boils at its boiling point.

2. The boiling point of pure water is 100 oC.

3. The temperature remains constant at 100 oC untilwater boils completely.

5.1 Physical Characteristics of Water

When the temperature rises, the water particlesmove faster and further apart.

Therefore, the forces of attraction among theparticles grow weaker.

At 100 oC, water particles move so fast thatthey overcome the forces of attraction and

leave the liquid’s surface.

Waterbecomessteam!

5.1 Physical Characteristics of Water

5. Water conducts heat slowly. Water is a poorthermal conductor.

6. Water is also a poor electrical conductor.

7. The density of water varies with temperature.Pure water has the maximum density of 1 gper cm3 at 4 oC.

5.1 Physical Characteristics of Water

B. Effects of Impurities on the PhysicalCharacteristics of Water

1. Impurities in water can change thephysical characteristics of water. Sometimesthe change is noticeable and sometimes it is not.

5.1 Physical Characteristics of Water

Physicalcharacteristic

Example

Taste Purewateristastelessbutseawaterissalty.

Odour Purewaterisodourless.Waterwithdecayedmatterhasanunpleasantsmell.

Colour Purewateriscolourlessbutmuddywaterisbrownishincolour.

Density Purewaterislessdensethanseawater.

Electricalconductivity

Purewaterwithafewdropsofsulphuricacidcanconductelectricity.

Freezingpoint o

Purewaterfreezesat0Cbutseawaterfreezesatalowertemperature.

Boilingpoint o

Purewaterboilsat100Cbutseawaterboilsatahighertemperature.

2. Here are some examples:

5.1 Physical Characteristics of Water

Hydrogen Oxygen

5.2 Composition of Water

Composition of Water

1. Water is a compound. It is made of two differentelements.

Water

2. Water can be broken down to its elementsthrough electrolysis.

A method to break down a compound by passingan electric current through its liquid or solution

5.2 Composition of Water

Hydrogen isreleased at the

cathode

Oxygen isreleased at the

anode

5.2 Composition of Water

3. The volume of hydrogen released is alwaystwice the volume of oxygen released.

Hydrogen atoms

Each water molecule consists of one atom of oxygen andtwo atoms of hydrogen.

5.2 Composition of Water

Water is made up of one part of oxygen and two parts ofhydrogen.

Oxygen atom

4.

5. Therefore, scientists represent water with thefollowing formula:

H2OH – Represents the hydrogen atom

2 – Shows that there are two atoms of hydrogen

O – Represents the oxygen atom

5.2 Composition of Water

Applying the principle of water evaporationIn our daily life.

1. To drying clothes2. To drying hair3. To drying agricultural produce4. To drying fish and prawn5. To cooling the body6. To producing the common salt

Solution and Solubility

5.4 Solution and Solubility

1. What is a solution?

• A solute is thesubstance that dissolves.

• A solvent is thesubstance that the solutedissolves in.

5.4 Solution and Solubility

Dilute solution

Contains a littledissolved solute

Can dissolve a lotmore solute

Concentrated solution

Contains a lot ofdissolved solute

Can dissolve a little bitmore solute

Saturated solution

Contains the maximumamount of dissolved solute

Cannot dissolve any moresolute

All these solutions have a clear appearance

5.4 Solution and Solubility

2. Depending on the amount of solutes insolutions, there are three types of solutions.

Solution

1. What is a suspension?

A suspension is a mixture containing insolublesubstances.

2. There are many suspensions around us.

Muddy water, fruit juices, chocolate drink, blood

5.4 Solution and Solubility

1. What is ‘solubility’?

The solubility of a solute is the maximum amount of solute ingrams that will dissolve in 100 g of solvent at a given

temperature.

For example, the solubility of sodium chloride is 38 g per 100g of water at 20 oC.

This means that you can dissolve not more than 38 g of sodiumchloride in 100 g of water at 20 oC.

5.4 Solution and Solubility

2. Factors Affecting the Solubility of a Solute

a. The nature of the solvent

b. The nature of the solute

c. The temperature of the solvent

5.4 Solution and Solubility

i. The nature of the solvent

- The solubility of a solute differs indifferent solvents.

Example:

Only a little iodine can dissolve in water. Iodine candissolve very well in alcohol.

5.4 Solution and Solubility

ii. The nature of the solute

Different solutes have different solubilityin the same solvent.

Example:

At the same temperature, sodium chloride has alower solubility in water compared to copper chloride.

5.4 Solution and Solubility

1. What are the factors affecting the rateof dissolving a solute?

a. Temperature

b. Rate of stirring

c. Size of solute particles

5.4 Solution and Solubility

i. Temperature

The higher the temperature of the solvent, the higher therate of dissolving.

:

We use hot water to maketea. One reason for this isthat hot water increasesthe rate of dissolving ofcertain substances in thetea leaves.

5.4 Solution and Solubility

ii. Rate of stirring

The higher the rate of stirring, the higher the rate ofdissolving.

:

The faster you stir thesoup, the faster the saltdissolves in it.

5.4 Solution and Solubility

iii. Size of solute particles

The smaller the size of the solute particles, the higher therate of dissolving.

Smaller pieces of palmsugar can dissolve in waterfaster than a big piece ofit.

5.4 Solution and Solubility

Water is a good solvent. Almost everything can dissolve in it toproduce solutions. Therefore, water is also known as the

universal solvent.

Water acts as a medium in many chemical reactions inour body.

Water dissolves and transports many substances in ourbody such as digested food and waste products.

Water dissolves cleaning agents such as soap powder,dishwasher liquid and toilet cleaner.

5.4 Solution and Solubility

Water dissolves various substances. This enables us touse water in cooking and making drinks.

Water is used extensively in food industry as a solvent.

Water is used to prepare traditional and modern liquidmedicines.

Farmers use water to dissolve pesticides.

Water is needed in plants to transport food anddissolved minerals.

5.4 Solution and Solubility

• Alcohol • Turpentine • Acetone

5.4 Solution and Solubility

Some substances cannot dissolve in water but they candissolve in organic solvents.

What are organic solvents?

Organic solvents are carbon compounds that are usedas solvents.

Examples:

1. We use many organic solvents in various products.

To produce lacquers and varnishes

Alcohol

Turpentine

Acetone

To produce various types of ink

To prepare iodine solution (as an antiseptic)

To produce perfume

To produce paints

To remove paint stains

To produce nail polish

To remove nail polish

5.4 Solution and Solubility

2. Organic solvents are very useful to us.

a. They are volatile. Therefore, products such aspaints, lacquers, varnishes and inks become dry in ashort period of time.

b. They can dissolve many solutes that do not dissolvein water.

3. However, products containing organic solventsshould be handled carefully.

a. They are flammable and should be stored awayfrom heat.

b. They are toxic and carcinogenic (likely to causecancer).

5.4 Solution and Solubility

1.

2.

An acid is a substance that has a hydrogenatom, which can be replaced by a metalor ammonium.

Acid can be divided into two groups anddifferences are shown below

ACID

Organic acid

ExampleAcetic acidFormic acidLactic acidMalic acidCitric acidTannic acidTartaric acid

Inorganic acid

ExampleSulphuric acidNitric acidHydrochloric acidCarbonic acid

3.An acid exist in three state which area. solid – tartaric acidb. liquid – ethanoic acidc. gas – hydrogen chloric

4. The properties of acidsa. Taste sourb. Are corrosivec. Change blue litmus paper to redd. Have pH values of less than 7e. React with carbonates to release carbon dioxide

and form salt and water

acid + cabonates salt + water + carbon dioxide

f. React with active metals to release hydrogen and formsalt.

g. React with alkalis to form salt and water

acid + metal salt + hydrogen

acid + alkali salt + water

1.

2.

An alkalis is hydroxide or metal oxide thatdissolves in water.

Example: potassium hydroxide, sodiumhydroxide, calcium hydroxide, ammoniumhydroxide solutions.

1 2 3 4 5 6 7 8 9 10 11 12 13 14

neutral

Acidity increases Alkalinity increases

acid + alkali salt water+

Note:

Neutralisation

Neutralization is a process where

Where acid reacts with alkali, salt and water are formed.

Different kinds of acids and alkalis will form different types of salt.

5.5 Acid and Alkali

Natural Sources of Water

Natural Sources of Water

From Ocean

• Salty• Not suitable forhuman consumption

From lakes, streams,rivers, ground water

(well) and rain

• Fresh Water• But not pure, need to be purified

5.6 Water Purification

a. Most pure

b. Has very little dissolved substances and alittle dust

a. Not clean

b. Has a lot of dissolved substances and dirtsuch as microorganisms and silt

a. Has microorganisms and dissolvedsubstances

b. Cleaner than river

a. Has the most substances of salt

b. Has the most of dirt.

Usage of Water

Usage of Water

Domestic Useof Water

• Drinking• Washing• Watering

Plants

Agricultural Useof Water

• Irrigation• Aquaculture •

••

Direct Use ofRivers and

Streams

GenerateHydroelectricPowerRecreationTransportation

Industrial Useof Water

• Cooling• Washing• Disposal

of Waste

5.7 Water Supply System

Chlorine solution

METHOD OF PURIFICATION

Chlorination

Filtration

Muddy water

Fine sand

Coarse sand

Pebbles

Gravel

filtrate

filtrate

Boiling

Distillation

MuddyWater

Waterout

Water in

Liebigcondenser

Distilledwater

1. Water from natural sources have variousimpurities such as microorganisms, dissolved gases,mineral salts and silt.

2. Water from natural sources must be purified so that itsave to drink and use.

3. Table shows the advantage and disadvantage ofwater purification.

Waterpurificationmethod

advantage disadvantage

a. FiltrationOnlyremovesimpuritiesthatarecoarsesuchassuspendedsubstances.Sandfiltersarecommonlyused

Waterisclearandfree

suspendedparticlesonly

Waterstillhasmicroorganismsanddissolved

substances(suchasmineralsalts)

b. Distillation

Prepares pure ordistilled water

Water is freefrom allsuspendedsubstances,microorganismsand dissolvedsubstances.

Water doesnot makegooddrinkingbecause itdoes notcontaindissolvedmineralwith ourbody need.

c. Boiling and

chlorination

Only killsmicroorganisms inwater

Water is free fromdangerousmicroorganisms

Water still hasdissolvedsubstances andsuspendedsubstances.

WATER TREATMENT PLANT

1. Refer to your text book pg. 36 and draw figure 5.34

PRESERVATION OF WATER QUALITY

1. Find out the ways to control water pollution on page 41.