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3 - METALS AND NON-METALS

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3 - METALS AND NON-METALS Powered By Docstoc
					Q.1 what is metallic lustre?
Ans. metals, in their pure state, have a shining surface. This property is called
metallic lustre.

Q.2    what do you mean by malleability?
Ans. the property of a substance of being able to be beaten into thin sheets is called
malleability.

Q.3    which are the most malleable metals?
Ans.   gold and silver.

Q.4    what is ductility?
Ans.   the ability of metals to be drawn into thin wires is called ductility.

Q.5    which is the most ductile metal?
Ans.   gold

Q.6    which properties of metals are used in making various shapes?
Ans.   malleability and ductility.

Q.7    why are metals used to make cooking vessels?
Ans. metals are used to make cooking vessels because they are good conductors of
heat and have high melting points.

Q.8 name the best conductors of heat.
Ans. silver and copper

Q.9    name 2 metals which are poor conductors of heat.
Ans.   lead and mercury

Q.10 write the full form of PVC. Why is it used to coat electric wires?
Ans. PVC stands for PolyVinylChloride. It is used to coat electric wires to prevent
electric shocks as PVC is an insulator.

Q.11 what do you mean by sonorousity?
Ans. the property of a substance to produce sound on striking a hard surface is
called sonorousity.

Q.12 why are school bells made of metals?
Ans. school bells are made up of metals to produce vibrating sounds as metals are
sonorous.

Q.13   name a non-metal which is liquid at room temperature.
Ans.   bromine

Q.14   name a metal which is liquid at room temperature.
Ans.   mercury

Q.15 name 2 metals which can melt even when you keep it on your palm. Give
reason why it happens.
Ans. gallium and caesium are the 2 metals which will melt if we keep them on our
palms, because they have very low melting points.

Q.16   name 1 non-metal which is lustrous.
Ans.   iodine

Q.17 what are allotropes of carbon?
Ans. the various forms in which carbon exists, are called allotropes of carbon. e.g.,
diamond, graphite, coke, etc.

Q.18   name 1 non-metal which is hard.
Ans.   diamond

Q.19   which is the hardest element?
Ans.   diamond

Q.20   name a non-metal that has a very high melting and boiling point.
Ans.   diamond

Q.21   name a non-metal that can conduct electricity.
Ans.   graphite

Q.22   name the metals which can be cut with knife.
Ans.   alkali metals (lithium, sodium and potassium)

Q.23 name some metals having low densities and low melting points.
Ans. lithium, sodium and potassium

Q.24 what is the nature of oxides of metals?
Ans. basic

Q.25 what is the nature of oxides of non-metals?
Ans. acidic

Q.26 state the physical properties of metals with exceptions?
Ans. 1) metals have lustre. (Except sodium, potassium)
       2) Metals are generally hard (except sodium, potassium, lithium)
       3) Metals are malleable (except sodium, potassium, lithium)
       4) Metals are ductile (except sodium, potassium lithium?
       5) Metals are good conductors of heat and electricity. (Except mercury, lead)
       6) Metals are sonorous (except mercury, sodium, lithium, potassium)
       7) Metals have very high boiling and melting points (except mercury, caesium,
       and gallium).
       8) Metals are solid at room temperature. (Except mercury which is liquid)

Q. 27 Q.26 state the physical properties of non-metals with exceptions?
Ans. 1) non-metals don’t have lustre. (Except iodine, diamond)
       2) Non-metals are generally soft (except diamond)
       3) Non-metals are brittle.
       4) Non-metals are bad conductors of heat and electricity. (Except graphite)
       5) Non-metals are non-sonorous.
       6) Non-metals have low boiling and melting points (except diamond)
       7) Non-metals are either solid or gas at room temperature. (Except lithium
       which is liquid)

Q.28   what happens when metals are burnt in air?
Ans.   almost all metals combine with oxygen (air) to form metal oxides.
       Metal + Oxygen ―› Metal oxide

Q.29   what happens when copper is heated in air?
Ans.   when copper is heated in air; it combines with oxygen tot form a black oxide.
              2Cu + 3O2 ―› 2CuO
                            (Copper (II) oxide)

Q. 30 what are amphoteric oxides?
Ans. metals oxides which react with both acids as well as bases to form salt and
water are known as amphoteric oxides. e.g., Aluminium oxide, Zinc oxide, etc.

Q.31   name 2 metal oxides which dissolve in water to form alkalis.
Ans.   sodium oxide and potassium oxide

Q.32 why are sodium and potassium kept in kerosene oil?
Ans. - sodium and potassium react so vigorously with oxygen and water that they
catch fire if kept in the open.
        - Hence to protect them and to prevent accidental fires, they are kept
             immersed in kerosene oil.

Q.33   what happens when metals react with water?
Ans.   metals react with water to produce metals oxide and hydrogen gas.

Q. 34 name 3 metals which react with cold water.
Ans. sodium, potassium and calcium

Q.35 why do sodium and potassium catch fire when water is poured on them?
Ans. the reaction of sodium and potassium with water is so violent and exothermic
that the evolved hydrogen gas immediately catches fire.

Q.36   why does calcium start floating when poured in water?
Ans.   - calcium reacts with water to form calcium oxide and hydrogen gas.
       -calcium starts floating because the bubbles of hydrogen gas formed stick to
       the surface of the metal.

Q. 37 name a metal which reacts with hot water but not with cold water.
Ans. magnesium

Q. 38 why does magnesium start floating on hot water?
Ans - magnesium reacts with hot water to form magnesium oxide and hydrogen
gas.
       -it starts floating because the bubbles of hydrogen gas formed stick to the
       surface of the metal.
Q.39   name some metals which react with steam but not with hot or cold water.
Ans.   aluminium, iron and zinc

Q.40   name some metals which do not react with water at all.
Ans.   lead, copper, silver and gold.

Q.41 generally metals react with acids to form salt and hydrogen gas. But hydrogen
gas is not evolved when nitric acid is treated with a metal. Give reason.
Ans. - nitric acid, being a strong oxidising agent, oxidises the H2 gas produced to
water and itself gets reduced to any of the nitrogen oxides (N2O, NO, NO2).
        -so instead of hydrogen gas, water is evolved.

Q. 42 name the metals which can evolve hydrogen gas even when reacted with nitric
       acid.
Ans. magnesium and manganese react with very dilute nitric acid to evolve
       hydrogen gas.

Q.43 A and B are metals. A + BSO4 ―› ASO4 + B. is the following reaction
possible: ASO4 + B ―› A+ BSO4 ? Give reasons. Which one is more reactive, A
or B?
Ans. - in the first reaction, A being more reactive than B displaces B.
       -but in the second reaction, B being less reactive than A, cannot displace A
       and so the reaction will not take place.

Q.44 arrange Na, Al, Ca, Cu, Au, Ag, K, Pb, Fe, Zn, Hg, H, Mg in decreasing order
of reactivity.
Ans.
            1. K   Potassium
            2. Na  sodium
            3. Ca  calcium
            4. Mg  magnesium
            5. Al  aluminium
            6. Zn  zinc
            7. Fe  iron
            8. Pb  lead
            9. H   hydrogen
            10. Cu copper
            11. Hg mercury
            12. Ag silver
            13. Au gold

Q.45 name some noble gases. Why do they occur in pure state and don’t react with
any element?
Ans. -helium, neon and argon are some of the noble gases.
       -they have a completely filled valence shell and so they are highly stable.
       -therefore they occur in pure state and don’t react with any other element.

Q.46   name the cation and anion in MgCl2.
Ans.   cation – Mg
       Anion - Cl

Q.47   which among cation and anion is positive?
Ans.   cation

Q.48   what are ionic compounds?
Ans.   the compounds formed by the transfer of electrons from a metal to a non-metal
       are known as ionic compounds or electrovalent compounds.

Q.49 what are the general properties of ionic compounds?
Ans.
   1. Physical nature: ionic compounds are             solids and hard because of the
      strong force of attraction between the positive and negative ions. These
      compounds are generally brittle.
   2. Melting and boiling points: ionic compounds have high melting points because
      a considerable amount of energy is required to break the strong inter-ionic
      attraction.
   3. Solubility: electrovalent compounds are generally soluble in water and
      insoluble in solvents such as kerosene, petrol, etc.
   4. Conduction of electricity: ionic compounds in the solid state do not conduct
      electricity because movement of ions in the solid is not possible due to their
      rigid structure. But in molten state, the electrostatic forces of attraction are
      overcomed by heat, and the compounds conduct electricity.


Q.50. what is a mineral?
Ans. An element or a compound which occurs naturally in the earth’s crust is known
as mineral.

Q.51 what are ores?
Ans. minerals which contain a very high percentage of a particular metal and the
metal can be profitable extracted from it, are called ores.

Q.52   give some examples of corrosion.
Ans.
           1. Silver articles become black after some time when exposed to air. This
              is because it reacts with sulphur in the air to form a coating of silver
              chloride.
           2. Copper reacts with moist carbon dioxide in the air and slowly loses its
              shiny brown surface and gains a green coat (copper carbonate).
           3. Iron when exposed to moist air for a long time acquires a coating of a
              brown flaky substance called rust.

Q.53 suggest some methods to prevent rusting of iron.
Ans. the rusting of iron can be prevented by painting, oiling, greasing, galvanising,
chrome plating, anodising or making alloys.

Q.54 what is galvanisation?
Ans. galvanisation is a method of protecting steel and iron from rusting by coating
them with a thin layer of zinc.
Q.55 the galvanised article is protected against rusting even if the zinc coating is
broken. Why?
Ans. when the zinc coating is broken, it immediately reacts with air to form an
impervious layer of zinc oxide which prevents attack of air, and thus protects it from
further corrosion.

Q.56 why is iron never used in pure state?
Ans. iron is never used in its pure state because pure iron is very soft and stretches
easily when hot.

Q.57 how is pure iron made strong and hard?
Ans. iron is mixed with a small amount of carbon (0.05%) to make it strong and
hard.

Q.58 how is iron alloyed to make it rust proof?
Ans. when iron is mixed with nickel and chromium, we get stainless steel, which is
hard and does not rust.

Q.59 what is an alloy?
Ans. an alloy is a homogeneous mixture of two or more metals, or a metal and a
non-metal.

Q.60 how is an alloy prepared?
Ans. alloy is prepared by first melting the primary metal, and then dissolving the
other elements in it in definite proportions. It is then cooled to room temperature.

Q.61 what is an amalgam?
Ans. if one of the metals in an alloy is mercury, then the alloy is known as an
amalgam.

Q.62 what is brass?
Ans. brass is an alloy of copper and zinc.

Q.63 what is bronze?
Ans. bronze is an alloy of copper and tin.

Q.64 what is solder and where is it used?
Ans. solder is an alloy of lead and tin, and is used for welding electrical wires as it
has a low melting point.

Q.65  what is the electrical conductivity and melting point of an alloy as compared
      to that of pure metals?
Ans. the electrical conductivity and melting point of an alloy is less than that of
pure metals.

Q.66   name some metals which are found in their free state in nature.
ans.   gold, silver, platinum and copper
Q.67 in which all forms are copper and silver found in nature?
ans. as pure metals, sulphide or oxide ores

Q.68     name some highly reactive metals which are never found in their free state.
ans.     potassium, sodium, calcium, magnesium, aluminium.

Q.69 name some of the metals in the middle of the reactivity series. in what state are
they found in nature?
ans. -zinc, iron, lead,etc are the metals in the middle of the reactivity series.
       -they are found in the earth’s crust mainly as sulphides and carbonates.

Q.70 why are ores of many metals oxides?
ans. the ores of many metals are oxides because:
    1. oxygen is a very reactive element
    2. oxygen is very abundant on the earth.

Q.71     what are the 3 categories of metals on the basis of reactivity?
ans.
    1.   metals of low reactivity
    2.   metals of medium reactivity
    3.   metals of high reactivity

Q.72 make a flow chart showing the steps involved in metallurgical process for all
three categories of metals.
ans. (learn from ncert science textbook pg 50 )

Q.73 what is gangue?
ans. ores mined from the earth are usually contaminated with large amounts of
impurities such as soil, sand ,etc., called gangue.

Q.74     what is the first step of metallurgy of any metal?
ans.     concentration of ore.

Q.75     what is cinnabar?
ans.     cinnabar is another name for mercury sulphide(HgS).

Q.76    how are metals of low reactivity converted to pure form from their ores?
ans.    - metal oxides can be reduced to metals by heating alone.
        - metal sulphides are first heated in air to convert them to metal oxides, and
then the metal oxides are reduced to pure metals on further heating.

Q.77     in which reactivity category of metals would you place mercury(Hg)
ans.     metals of low reactivity

Q.78     what is roasting?
ans.     heating strongly in the presence of excess air is called roasting.

Q.79     what is calcination?
ans.     heating strongly in limited air is called calcination.
Q.80 how are metals of medium reactivity purified from their ores?
ans.
    1. – the sulphide ores are converted into oxides by strongly heating in presence
        of excess air(roasting).
        - the carbonate ores are changed into oxides by heating strongly in limited
        air(calcination).
    2. the metal oxides are then reduced to the corresponding metals by using
    suitable reducing agents such as carbon, or highly reactive metals like sodium,
    calcium, aluminium, etc which act as reducing agents by displacing metals of
    lower reacitivity.

Q.81 when the metal oxides are reduced using highly reactive metals, the metals are
obtained in molten state. why?
ans. -the highly reactive metals displace the metal oxides.
       - these displacement reactions are highly exothermic.
       - the amount of heat evolved is so large that the metals are produced in the
           molten state.

Q.82 what is thermit reaction?
ans. the exothermic reaction of iron(III) oxide (Fe2O3) and aluminium, which is
used to join railway tracks or cracked machine parts, is known as thermit reaction.

Q.83 why can’t carbon reduce the oxides of sodium, magnesium, calcium and
aluminium?
ans. carbon cannot reduce the oxides of sodium magnesium, calcium and
aluminium because these highly reactive metals have more affinity for oxygen than
carbon.

Q.84 how are the ores of metals of high reactivity reduced to their pure form?
explain.
ans. - the metals of high reactivity are obtained by electrolytic reduction of their
       ores.
       - it is the process of reducing the metals by electrolysis of their molten ores.
       - the metals are deposited at the cathode and the electronegative compounds
           of the ores are deposited on the anode.

Q. 85 which electrode is negatively charged and which is positively charged?
ans. cathode is negatively charged while anode is positively charged.

Q. 86 on which electrode do metals stick during electrolytic reduction? why?
ans. metals stick on cathode, because metals are electropositive and cathode is
negatively charged.

Q. 87 what is the last step involved in metallurgical process? explain.
ans.   -the last step involved in the metallurgical process is refining of metals by
      electrolytic refining.
      - in this process, the impure metal is made the anode and thin strip of pure
          metal is made the cathode. a solution of the metal salt is used as an
          electrolyte.
       -   on passing the current through the electrolyte, the pure metal from the
           anode dissolves into the electrolyte.
       -   an equivalent amount of pure metal from the electrolyte is deposited on the
           cathode.
       -   the soluble impurities go into the solution, whereas the insoluble
           impurities settle down at the bottom of the anode and are known as anode
           mud.

Q.88 what is anode mud?
ans. the insoluble impurities that settle down at the bottom of anode, during
electrolytic refining of metals, is called anode mud.

				
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