Revision on soap and detergentStructure

Cleansing actionCompare soap and detergent

•the organic part •the ionic part

•the hydrophobic part •the hydrophilic part

• the head part•the tail part

STRUCTURE of SOAP PARTICLE

STRUCTURE OF DETERGENT PARTICLE

CLEANSING ACTION OF SOAP OR DETERGENT.

a) State three abilities of both soap and detergent that enable them to act as cleansing agents

i.Ability to lower the surface tension of water

This helps to wet the cloth better

ii. To emulsify oil or grease,

(break the oil or grease into smaller droplets)

iii. Suspend oil or grease in water,

Prevent the oil or grease from redeposit on the surface of the cloth

Describe the cleansing action of soap and detergent1) Soap dissolves in water and lowers the surface tension of water. This helps to wet the cloth better

2) The hydrophobic part ( tail part) dissolvesIn grease , the hydrophilic part ( head part) dissolves in water3) Movement of water during scrubbing helps to loosen the grease and lift the grease off the surface

4) Repulsion of negative charges break the grease into small droplets.

Rinsing washes away these droplets and leaves the cloth clean

d)Compare and contrast the cleansing action of soap and detergents

Property Soap Detergent

1 sources

2 Molecular structure

3 Effectiveness in hard water

4 Effectiveness in acidic water

5 Cleaning power

6 Effect to the environment

Made from plant or animal Made from petroleum fractions

R – COO – Na +

Where R is alkyl group

R SO4 – or

Forms scum with hard water

Does not form scum with hard water

Forms precipitate with acidic water

Does not form precipitate with acidic water

Less powerful More powerful

Biodegradable and do not cause any pollution

Some detergents are non biodegradable and kill aquatic lives

Explain the difference

Hard water contains Mg 2+ ions and Ca 2+ ions • Detergent form soluble

salt with Mg 2+ ions and Ca 2+

• No scum is formed, • so detergent can function

as cleaning agent

• But soap form insoluble salt with Mg 2+ ions and Ca 2+

• Scum is formed , • so soap cannot function as

cleaning agent

soapdetergent

Revision on rusting of iron

Conditions for rustingDescribe process of rusting

Effect of other metals on rusting of iron

Ways to prevent rusting of iron

a)State conditions of rusting

b) State the function of oxygen and iron in the rusting of iron b) Oxygen is the oxidizing agent and Iron is the reducing agent

a) Presence of water and oxygen

DESCRIBE PROCESS OF RUSTING IN TERMS OF OXIDATION AND REDUCTION REACTION

cathode cathodeanode e

Fe 2+

Step 1- At anode, iron atom is oxidized to form iron(II) ions

Step 2- Electron flow through metal to cathode where there are plenty of dissolved oxygen- Electron are gained by Oxygen to form hydroxide ions

Step 3- iron (II) ions combined with hydroxide ions to form iron(II) hydroxide

Step 4- the iron(II) hydroxide rapidly oxidesed by oxygen to form RUST

Revision on Rusting of iron

Revision on Rusting of iron

WHAT IS THE FUNCTION OF A)POTASSIUM HEXACYANOFERATE(III) SOLUTION)?

B) PHENOLPHTHALEIN?

C) AGAR?

TO DETECT THE PRESENCE OF IRON(II) ION

TO DETECT THE PRESENCE OF HYDROXIDE ION

TO TRAP THE COLOUR FORMED DURING REACTION

A)WHY DOES THE PHENOLPHTAHLEIN CHANGE TO PINK IN IRON NAIL WITH MAGNESIUM?

B)WHICH METAL UNDERGO CORROSION?

C) WRITE HALF EQUATION FOR THIS REACTION

D)WHAT IS THE ROLE OF MAGNESIUM IN THIS EXPERIMENT?

Presence of OH- ion

magnesium

Mg Mg2+ + 2e

To protect iron from rusting

Revision on Rusting of iron

A)WHY DOES THE POTASSIUM HEXACYANOFERRATE(III) CHANGE TO BLUE IN IRON NAIL WITH COPPER?

B)WHICH METAL UNDERGO CORROSION?

C) WRITE HALF EQUATION FOR THIS REACTION

D)WHAT IS THE ROLE OF COPPER IN THIS EXPERIMENT?

Presence of Fe 2+ ion

iron

Fe Fe 2+ + 2e

To encourage rusting of iron

Revision on Rusting of iron

A)WHAT IS THE ROLE OF METALS THAT ARE IN CONTACT with iron IN THE RUSTING OF IRON?

Metals which are above iron in ECS inhibit iron from rusting

Metals which are below iron in ECS encourage rusting of iron

Ways to prevent RUSTINg of iron• Alloying • In stainless steel Iron is alloyed with carbon, chromium

and nickel• Chromium and nickel forms a layer that does not rust

• Sacrificial protection

• Iron is connected to a more electropositive metal, example magnesium or zinc• Mg or Zinc will corrode first, so protect iron from rusting

• Galvanising • iron or steel is coated with a thin layer of zinc• When scratched, zinc will corrode first because zinc is

more electropositive than iron

• Tin plating • sheets of steel are coated with a thin layer of tin• But if scratched, iron will rust, because tin is less

electropositive than iron

Explain the difference

In test tube 1Blue colour shows presence of Fe 2+ ionsIron nail rusts , due to presence of water and oxygen

Fe Fe 2+ + 2e

In test tube 2• High intensity of pink colour shows high conc of OH – ions • NO rusting of iron occur, Magneium undergo corrosion

• Mg is more electropositive than iron, so protect iron from rustingMg Mg2+ + 2e

In test tube 3• High intensity of blue colour shows high conc of Fe 2+ ions• Iron nail rusts , • Copper is less electropositive than iron, so • Copper encourage rusting of iron

Fe Fe 2+ + 2e

Revision of Rubber and coagulation

of latexHow coagulation of

latex occurVulcanisation of rubber

LATEX BEFORE ACID IS ADDEDRubber molecules repel each otherNo coagulation occur

ADD ACID, or bacteria acts on latex to produce lactic acid. (H + IONS) neutralize the negatively charged of rubber articles

Rubber particles collideRubber membranes rapture

rubber molecules combine, coagulation occur

HOW coagulation of latex occur

VULCANISED RUBBER a) What is meant by vulcanization of rubber?

ADDITION OF SULPHUR TO RUBBER AT 140 OC AND HIGH PRESSURE IN THE PRESENCE OF ZINC OXIDE AS THE CATALYST

By heating latex with SULPHUR or a solution of sulphur monochloride in methylbenzene as solvent

b) In industry, how does the vulcanization of rubber is carried out?

C) DESCRIBE HOW SULPHUR ATOMS CHANGE THE PROPERTIES OF RUBBER

•In vulcanization …………..atoms form …………………between rubber molecules •These …………………….prevent rubber……………………… from sliding too much when …………………………….The rubber molecules return to their ………………... position after being stretched.

d) Draw cross-linkage of sulphur

sulphur cross-link cross – LINK MOLECULES

•STRETCHED ORIGINAL

E) COMPARE AND CONTRAST THE PROPERTIES OF VULCANIZED AND UNVULCANISED RUBBER

Differences Vulcanised Unvulcanised rubber Elasticity

Hardness

Tensile strength

Resistance to heat

Effect of organic solvents

•Differences

Both are ELASTIC Both do not CONDUCT HEAT AND ELECTRICITY

More elastic LESS elastic

Harder SOFTER

More tensile strength LESS tensile strength

More resistance to heat LESS resistance to heat

LESS SOLUBLE MORE SOLUBLE

•Similarities

G) STATE ONE ADVANTAGE OF NATURAL RUBBER OVER SYNTHETIC RUBBER

Natural rubber is made from latex of rubber treeSynthethic rubber is man-made rubber from chemical substance

F) WHAT IS THE DIFFERENCE BETWEEN NATURAL RUBBER OVER SYNTHETIC RUBBER IN TERMS OF SOURCE ?

Only natural rubber can absorb the high STRESS, STRENGH AND HEAT ………( in tyres) produced during landing and taking off of an aero plane