Form 4 / Combined Science (Chemistry Part) / Reading ...

Form 4 / Combined Science (Chemistry Part) / Reading Assignment 2 / 1

Heep Woh College F.4 Combined Science (Chemistry Part) Reading Assignment 2

Group Name: ______________________________

Class: 4 ( )

Group Member: 1. _______________________ ( ) 2. _______________________ ( )

3. _______________________ ( ) 4. _______________________ ( )

Part I: Read the following passage and answer the questions below.

Aluminium ? a versatile metal

Aluminium is the world's most abundant metal, and the third most abundant element overall, after oxygen and silicon. It makes up about 8% by mass of the Earth's crust.

Properties of aluminium Applications of aluminium reflected its properties, in particular its low density, corrosion resistance and electrical conductivity.

Strength to mass ratio Aluminium has a density about third that of steel. It is used in applications where high strength and low mass are required.

Corrosion resistance When the surface of aluminium is exposed to air, an oxide layer forms almost instantaneously. This oxide layer protects the metal beneath from further attack.

Electrical and heat conductivities Aluminium is an excellent conductor of both electricity and heat.

Toxicity Aluminium is non-poisonous. In addition to that, it does not release any odours of taint products with which it is in contact.

Application of aluminium

Packaging Aluminum is probably the most versatile packaging material available today.

Aluminium foil is totally opaque to ultraviolet light, which can quickly cause deterioration of many foods. it is also impervious to gases and water vapour. Aluminium foil is also strong, non-poisonous and show good heat and cold resistance. Thus, aluminium foil is used in many applications, such as pharmaceutical and food packaging.

Heavier foil containers are used for convenience foods and take-away meals.

S.Mo & C.K.Lau

Form 4 / Combined Science (Chemistry Part) / Reading Assignment 2 / 2

The aluminium beverage can is popular because it is light, unbreakable and the most recyclable package.

Transport The high strength and low density of aluminium makes it the prime material for the construction of aircraft. Low mass results in reduced fuel consumption.

Various aluminium alloys are also used in the construction of trains, ships, buses and bicycles.

Building and architecture The lightness of structure made of aluminium makes them much easier to handle. It also costs less to support these structures. Its self-protecting oxide layer means that aluminium needs no further treatment against oxygen in the air.

Aluminium used in buildings covers a wide range of applications, such as window frames, roofing, shop fronts and architectural hardware.

Question:

1. Aluminium is used to make overhead power transmission lines. List properties of aluminium that make it suitable for this application.

____________________________________________________________________________

____________________________________________________________________________

____________________________________________________________________________

____________________________________________________________________________

2. Tin-plated steel had been used to make food cans since the invention of canned food. Aluminium is now being used to make cans too. Suggest ONE advantage and ONE disadvantage of using aluminium to make food cans.

____________________________________________________________________________

____________________________________________________________________________

____________________________________________________________________________

____________________________________________________________________________

____________________________________________________________________________

____________________________________________________________________________ End of Part I

S.Mo & C.K.Lau

Form 4 / Combined Science (Chemistry Part) / Reading Assignment 2 / 3

Part II: Read the following passage and answer the questions below. Can Gold and Silver be corroded?

In Ancient China, people used to represent gold and to represent silver. This is because gold always shines golden yellow like the Sun while silver always shines silvery white like the Moon. Gold and silver usually do not corrode because they are extremely unreactive. They seldom combine with other elements. Even when they are heated to 1000oC or above, they still do not react with oxygen. The Chinese saying "good gold endures the fire" is derived from the phenomenon that gold does not have chemical change even on strong heating. Therefore, the gold ores and some silver ores in nature are pure. Until now, the biggest piece of gold discovered in nature weighed 112kg while the biggest piece of silver weighed 13.5 tonnes! Almost all of the other metals exist as compounds, e.g. iron ore: iron oxides, zinc blende: zinc sulphide, bauxite: aluminium oxide, cassiterite: tin(IV) oxide, galena: lead(II) sulphide, etc. However, gold and silver sometimes do corrode. Gold corrodes in aqua regia. Aqua regia is the strongest acid. It is a mixture of concentrated nitric acid and concentrated hydrochloric acid in a ratio of 1:3 by volume. It reacts with gold and forms compounds which are soluble in water. Silver is more reactive than gold. Apart from aqua regia, silver also react with sulphur to form black silver sulphide. Once shiny silver vessels are in touch with sulphur powder, they turn black. Therefore, ancient vessels made of silver are always black in colour but those made of gold still shine. If you clean the silver vessels with ammonia solution, the blackened surface will turn shiny quickly. This is because the covering silver sulphide reacts with ammonia solution and forms soluble silver ammonia complex. Similarly, blackened copper vessels can be cleaned by ammonia solution. Therefore, ammonia solution is also called "copper cleaner".

S.Mo & C.K.Lau

Questions

Form 4 / Combined Science (Chemistry Part) / Reading Assignment 2 / 4

1. How do we know that gold and silver are extremely unreactive metals?

____________________________________________________________________________

____________________________________________________________________________

____________________________________________________________________________

2. In what form do other metals exist? Give two examples.

____________________________________________________________________________

____________________________________________________________________________

____________________________________________________________________________

3. What is the composition of aqua regia?

____________________________________________________________________________

____________________________________________________________________________

____________________________________________________________________________

4. Apart from aqua regia, what substance also corrodes silver? What is the product?

____________________________________________________________________________

____________________________________________________________________________

____________________________________________________________________________

5. How can we remove the black substance on silver vessels? What is the underlying principle?

____________________________________________________________________________

____________________________________________________________________________

____________________________________________________________________________

The End

S.Mo & C.K.Lau

 ................
................

In order to avoid copyright disputes, this page is only a partial summary.

Google Online Preview   Download