Science [3 Mark Questions]

1. X(12): 2,8,2

Valency: 2

2. Less reactive than Ca as reactivity increases down the group.
3. It is a metal.
4. Formula of oxide: XO

Iron when exposed to moist air for a long time acquires a coating of a brown flaky substance rust and this process is called rusting/ corrosion of iron in moist air/ slow oxidation of iron in moist air. Diagram
Activity description:

• Take three test tubes and place clean iron nails in each of them.
• Label these test tubes A, B and C. Pour some water in test tube A and cork it.
• Pour boiled distilled water in test tube B. add about 1 ml of oil and cork it. The oil will float on water and prevent the air from dissolving in the water.
• Put some anhydrous calcium chloride in testtubeCand cork it. Anhydrous calcium chloride will absorb the moisture, if any, from the air Leave these test tubes for a few days and then observe. It is observed that iron nails in test tube A rust where as those in Band C do not.

• Oxidation of iron when exposed to air and moisture and acquiring a coating of brown flaky substance. Activity-
• Take three test tubes marked A,B and C with clean iron nails in each.
• Pour some water in test tube ‘A’ and cork it.
• Pour some boiled distilled water and a drop of oil in test tube B and cork it.
• Put some anhydrous calcium chloride in test tube ‘C’ and cork it. It will absorb moisture from air leave the test tubes for a few days.
• Rusting will take place only in test tube A, which has air and moisture present.

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Zinc is more electropositive than Iron but it does not get corroded faster and is used to galvanize iron.
Reasons:

• A thin layer prevents the entering of water and oxygen underneath.
• Zinc is more reactive than iron.
• Oxidizes in preference to the iron.
• Corrosion is because when oxygen in the air reacts with the surface of zinc.
• Dense and impermeable coating of zinc oxide.
• Acts as a physical barrier that protects the zinc surface.

1. Alloys are stronger than the metals from which they are made.
2. Alloys are harder than the constituent metals.
3. Alloys are more resistant to corrosion.
4. Alloys have lower melting points than constituent metals.
5. Alloys have lower electrical conductivity than pure metals.

1. Mineral: The naturally occurring compounds of elements are known as Mineral.
2. Ore: Minerals from which metals can be extracted profitably are known as ores.
3. Gaguen: The impurities present in the ore such as sand, rocks etc are non as gangue.

X loses 2 electrons while Y gains 1. It means X is in group 2 and Y in group 17.

It is ionic. It has high melting point as it is a crystalline salt. Yes, it is soluble in water & conducts electricity in aqueous state and molten state.

Electroplating is basically the process of plating a metal onto the other by hydrolysis mostly to prevent corrosion of metal or for decorative purposes. The process uses an electric current to reduce dissolved metal cations to develop a lean coherent metal coating on the electrode. Electroplating is often applied in the electrical oxidation of anions on a solid substrate like the formation of silver chloride on silver wire to form silver chloride electrodes.
Electroplating is majorly applied to modify the surface features of an object (e.g corrosion protection, lubricity, abrasion), but the process can also be used to build thickness or make objects by electroforming.

Since nitrogen has 5 electrons in its outermost shell so, to achieve the 8-electron structure of an inert gas, it needs 3 more electrons and hence combines with another nitrogen atom to form a molecule of nitrogen gas.

This type of bonding is called covalent bonding.

1. Minerals: The natural materials in which the metals or their compounds are found in earth are called minerals.
2. Ores: Those minerals from which the metals can be extracted conveniently and profitably are called ores.
3. Gangue:The unwanted impurities like sand, rocky material, earthy particles etc. present in an ore are called gangue.

Zinc oxide is basically an inorganic compound. It is a white coloured powder. It occurs in the earth’s crust in natural form. For commercial purposes, zinc oxide is manufactured and is synthetic in nature.

Metals and non-metals can be differentiated on the basis of following chemical properties.

	Metals	Non-metals
1.	Metals displace hydrogen from water.	Non-metal do not displace hydrogen from water.
2.	Metals are basic oxide.	Non-metals are acidic oxides.
3.	Metals displace hydrogen from dilute acids.	Non-metals displace hydrogen from dilute acids.
4.	Metals form ionic chlorides with chlorides with chlorine.	Non-metals form covalent chlorides with chlorine.

Copper reacts with moist carbon dioxide in air to fonm copper carbonate and as a result, copper vessel loses its shiny brown surface forming a green layer of copper carbonate. The citric acid present in the lemon or tamarind neutralises the basis copper carbonate and dissolves the layer. That is why, tarnished copper vessels are cleaned with lemon or tamarind juice to give the surface of the copper vessel its characteristic lustre.

The metals in the middle of the reactivity series are moderately reactive. these are usually pesent as sulphides or carbonates in nature the metal sulphides and carbonates must be converted into metal oxides. Thus this impure metal ‘M’ undergoes purification. The process of purifying impure metal is called refining. The most widely used method for refining is electrolytic refining.

A substance that can be beaten into thin sheets is said to be malleable. For example, iron, copper etc.
A substance that can be drawn into wires is called ductile. For example, gold, silver etc.

1. A is a metal.
2. B and C are non-metals.
3. A and B combines to form an ionic bond.
4. B and C combines to form a covalent bond.
5. B will form an anion with valency 1 since it needs only 1 electron to complete its octet.

When a metal reacts with dilute acid, salts are formed. During this reaction hydrogen gas is evolved. In other words, when a metal is added to dilute acids, salt and hydrogen gas are formed.
Process: Sulfate salts and chloride salts are formed when metals react with dilute sulfuric acid and hydrochloric acid. Some metals reacts vigorously with dilute sulfuric acid or hydrochloric acid for example, potassium, sodium, lithium and calcium.

Metals lose their shine or brightness on keeping in air for a long time and acquire a dull appearence due to the formation of a thin layer of oxide, carbonate or sulphide on their surface by the slow action of various gases present in air.
Brightness of metals can be restored by rubbing the dull surface of the metal object with a sand paper, then the outer corroded layer is removed and the metal object becomes shiny and bright once again.

Different methods are used for extracting metals belonging to category of highly reactive metals, moderately reactive metals and less reactive metals. This is because the extraction of a metal from its concentrated ore is essentially a process of reduction of the metal compound present in the ore.
For example: Manganese metal is obtained by the reduction of its oxide with aluminium powder and not carbon. This is because carbon is less reactive than manganese. Carbon, which is a non-metal, is more reactive than zinc and it can be placed just above Zn in the reactivity series.
Hence, carbon can reduce the oxides of zinc and all other metals below zinc to form metals.

Two ways to prevent the rusting of iron are:
→ Oiling, greasing, or painting: By applying oil, grease, or paint, the surface becomes water proof and the moisture and oxygen present in the air cannot come into direct contact with iron. Hence, rusting is prevented.
→ Galvanisation: An iron article is coated with a layer of zinc metal, which prevents the iron to come in contact with oxygen and moisture. Hence, rusting is prevented.

There are some elements in group 18 of the periodic table which do not combine with other elements. These elements are helium, neon, argon, krypton, xenon and radon . They are known as noble gases or inert gases because they are unreactive.
If we look at the electronic configuration of noble gases, we would notice that except helium, all other inert gases have 8 electrons (helium has 2) in their outermost shells. This is considered to be the most stable arrangement of electrons.

Aluminium begins to corrode quickly when it comes in contact with moist air. The action of moist air on aluminium metal forms a thin layer of aluminium oxide all over the metal. This aluminium oxide is very tough and prevents the metal underneath from further corrosion. Therefore, aluminium is used for making utensils irrespective of its highly reactive property as its corrosion leads to the non-corrosion of the metal in the longer run.

We cannot use an aqueous solution of sodium chloride to obtain sodium metal because if we electrolyse an aqueous solution of sodium chloride, then as soon as sodium metal is produced at cathode, it will react with water present in the aqueous solution to form sodium hydroxide. Hence, electrolysis of an aqueous solution of sodium chloride will produce sodium hydroxide and not sodium metal.

We would create an apparatus using dry cell, a torch bulb fitted in a holder and some connecting wires with crocodile clips and connect them to make an electric circuit. Then insert a piece of sulphur between the crocodile clips and the bulb does not light up at all. This means that sulphur does not allow the electric current to pass through it. Now insert a piece of copper between the crocodile clips and the bulb will light up. This observation shows that non metals (ex- sulphur) do not conduct electricity and metals (ex- copper) conduct electricity.