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Science Answer the questions.[Che-3M]

Metals and Non-Metals · CBSE STD 10 (CBSE - English Medium). 88 questions.

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Answer the questions.[Che-3M]

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Question 13 Marks
Differentiate between metal and non-metal on the basis of their chemical properties.
Answer
Metals and non-metals can be differentiated on the basis of following chemical properties.
MetalsNon-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.
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Question 23 Marks
You must have seen tarnished copper vessels being cleaned with lemon or tamarind juice. Explain why these sour substances are effective in cleaning the vessels.
Answer
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.
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Question 33 Marks
The given reaction shows one of the processes to extract the metals like Iron and Manganese.
$
MnO _2( s )+ Al ( s ) \rightarrow Mn ( l )+ Al _2 O _3( s )+\text { Heat }
$
a) Give reason why the above reaction is known as a thermite reaction.
b) Identify the substance oxidised and reduced in the above reaction.
c) Give a reason why Aluminium is preferably used in thermite reactions.
Answer
a) The above reaction is known as a thermite reaction as the reaction is highly exothermic reaction.
b) Substance oxidised - $Al ( s )$
Substance reduced $- MnO _2$ (s)
c) Aluminium is preferably used in thermite reactions as it is placed above Fe and $Mn$ in reactivity series of metals.
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Question 43 Marks
A reddish-brown metal ' $X$ ', when heated in air, gives a black compound ' $Y$ ', which when heated in presence of $H _2$ gas gives ' $X$ ' back. ' $X$ ' is refined by the process of electrolysis; this refined form of ' $X$ ' is used in electrical wiring.
Identify ' $X$ ' and ' $Y$ '. Draw a well-labeled diagram to represent the process of refining ' $X$ '.
Answer
a) ' $X$ ' - Copper/ $Cu$ and ' $Y$ ' - $CuO$
b) Diagram to represent the process of refining of ' $X$
Image
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Question 53 Marks
An element ' $M$ ' with electronic configuration (2,8,3) combines separately with $Cl , SO ^2$ anions. Write the chemical formulae of the compounds formed. Predict with the suitable reason the nature of the bond formed by element ' $M$ ' in general. How will the electrical conductivity of the compounds formed vary with respect to 'M'?
Answer
$
MCl _3 ; M _2\left( SO _4\right)_3
$
$M$ in general forms Ionic bond. It can acquire a stable electronic configuration of neon $(2,8)$ by losing its three valence electrons to form $M ^{3+}$ cation.
Compounds formed will conduct electricity in liquid / molten state but not in solid state in contrast to ' $M$
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Question 63 Marks
  1. What are amphoteric oxides? Choose the amphoteric oxides from amongst the following oxides:

$\text{Na}_{2}\text{O, ZnO, Al}_{2}\text{O}_{3}, \text{CO}_{2}, \text{H}_{2}\text{O}$

  1. Why is it that non-metals do not displace hydrogen from dilute acids?
Answer
  1. Metal oxides that react with both acids and bases to produce salt and water are known as amphoteric oxides. For example, zinc reacts with an acid or a base to produce salt and water.

ZnO, Al2 O3 etc. are amphoteric oxides.

  1. Non-metals do not displace hydrogen from dilute acids is because unlike metals, non-metals do not have a tendency to lose electrons but to gain electrons.
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Question 73 Marks
The atomic number of an element is 12.
  1. Write its electronic configuration and determine its valency.
  2. Is it more reactive or less reactive than Ca (atomic number 20)? Justify your answer giving reason.
  3. Is it a metal or a non-metal?
  4. Write the formula of its oxide.
Answer
  1. X(12): 2,8,2

Valency: 2

  1. Less reactive than Ca as reactivity increases down the group.
  2. It is a metal.
  3. Formula of oxide: XO
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Question 83 Marks
The atomic number of an element is 19.
  1. Write the electronic configuration of this element and determine (i) the valency of this element, and (ii) whether this element is a metal or a non-metal.
  2. Write the formula of the oxide of this element.
  3. Is this element more reactive or less reactive than Na (atomic number 11)? Justify your answer giving example.
Answer
  1. X(19): 2,8,8,1
  1. Valency: 1
  2. X is a metal
  1.  X2O
  2. X is more reactive than Na X and Na belong to the same group. But Na is in the third period and X is in the fourth period. Since reactivity increases down the group X is more reactive than Na.
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Question 93 Marks
What is meant by ‘rusting’? With labelled diagrams describe an activity to find out the conditions under which iron rusts.
Answer
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.
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Question 103 Marks
  1. Show the formation of NaCl from sodium and chlorine atoms by the transfer of electron(s).
  2. Why has sodium chloride a high melting point?
  3. Name the anode and the cathode used in electrolytic refining of impure copper metal.
Answer
  1.  

 

  1. Sodium chloride consists of sodium ion (Na+) and chloride ion (CT). These are strongly attracted towards each other to form ionic bond. To break this strong force of attraction between them, a large amount of energy is required ..... Hence, sodium chloride has high melting point.

  2. Cathode: Strip of pure copper.

Anode: Crude (impure) copper.

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Question 113 Marks
What is 'rusting'? Describe with a labelled diagram an activity to investigate the conditions under which iron rusts.What is 'rusting'? Describe with a labelled diagram an activity to investigate the conditions under which iron rusts.
Answer
  • 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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Question 123 Marks
Zn is more electropositive than Fe. Therefore, it should get corroded faster than Fe. But it does not happen. Instead, it is used to galvanize iron. Explain why does it happen so?
Answer
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.
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Question 133 Marks
You are given a dry cell, a torch bulb with holder, wires and crocodile clips. How would you use them to distinguish between samples of metals and non-metals?
Answer
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.
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Question 143 Marks
Write the equations for the reactions of:
  1. Iron with steam.
  2. Calcium with water.
  3. Potassium with water.
Answer
The balanced chemical equations for the said reactions are as follows:

  1. Iron with steam:

$3\text{Fe(s)}+4\text{H}_2\text{O(g)}\rightarrow\text{Fe}_3\text{O}_4(\text{s})+4\text{H}_2(\text{g})$

  1. Calcium and water:

$\text{Ca(s)}+2\text{H}_2\text{O(l)}\rightarrow\text{Ca(OH)}_2(\text{aq})+\text{H}_2(\text{g})$

  1. Potassium and water:

$2\text{K(s)}+2\text{H}_2\text{O(l)}\rightarrow2\text{KOH(aq)}+\text{H}_2(\text{g})$

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Question 153 Marks
Write a displacement reaction for non-metal.
Answer
In this reaction, one anion replaces another one from its solution. An anion is a negatively charged ion or non-metal. For example, more reactive halogen replaces less reactive halogen from its solution.

  • Chlorine displaces bromine from an aqueous solution of sodium bromide.

$\text{Cl}_2(\text{g})+2\text{NaBr(aq)}\xrightarrow{\ \ \ \ \ \ \ \ \ \ \ \ \ }2\text{NaCl(aq)}+\text{Br}_2(\text{g})$

  • Bromine splaces iodine from potassium iodide solution.

$\text{Br(g)}+2\text{Kl(aq)}\xrightarrow{\ \ \ \ \ \ \ \ \ \ \ \ }2\text{KBr(aq)}+\text{l}_2(\text{aq})$

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Question 163 Marks
Will carbon monoxide (CO) change the colour of blue litmus?
Answer
Carbon is a nonmetal Oxides of nonmetal are acidic Oxides of nonmetal when dissolved in water acids are formed When carbon dioxide dissolves in water Carbonic acid. is formed.

$\text{H}_2\text{O}+\text{CO}_2\rightarrow\text{H}_2\text{CO}_3$

H2CO3 - is Carbonic acid

Hence here blue litmus solution turns red.

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Question 173 Marks
Why should the metal sulphides and carbonates be converted to metal oxides in the process of extraction of metal from them?
Answer

It is quite easy to obtain a metal from metal oxide by carrying its reduction with a suitable reducing agent. However, metal sulphides and carbonates are converted to the oxide form and then reduced.

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Question 183 Marks
Why ions move freely and conduct electricity in the molten form?
Answer
Ionic compounds are composed of two elements. The ionic bond between these two elements is strong. In solid state there is no availability of free electrons and also there is no probability for the formation of ions. So ionic compounds do not conduct electricity when they are solid, but they do conduct electricity when they are dissolved in water or when they are melted because in molten state these ionic compounds forms ions. these ions are responsible for the conduction of electricity.
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Question 193 Marks
When a metal X is treated with cold water, it gives a basic salt Y with molecular formula XOH (Molecular mass = 40) and liberates a gas Z which easily catches fire. Identify X, Y and Z and also write the reaction involved.
Answer
The atomic mass of metal X = 56 – Mass of OH group = 56 — 17 = 39u. This shows that the metal ‘X’ is potassium (K) and the basic salt ‘Y’ is potassium hydroxide (KOH). It is formed by reacting potassium with cold water. Hydrogen gas ‘Z’ evolved in the reaction catches fire.
2K(s) + 2H2O(aq) → 2KOH(aq) + H2(g)
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Question 203 Marks
What type of bonding would you expect between the following pairs of elements?
  1. Calcium and Oxygen.
  2. Carbon and Chlorine.
  3. Hydrogen and Chlorine.
Answer
  1. Ionic bonding.
  2. Covalent bonding.
  3. Covalent bonding.
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Question 213 Marks
What is the nature of zinc oxide?
Answer
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.
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Question 223 Marks
What is the difference between a cation and an anion? How are they formed? Give the names and symbols of one cation and one anion.
Answer
A positively charged ion is known as cation. A cation is formed by the loss of one or more electrons by an atom.
For example: sodium loses 1 electron to form a sodium ion, Na+, which is a cation.
A negatively charged ion is known as anion. An anion is formed by the gain of one or more electrons by an atom.
For example: A chlorine atom gains (accepts) 1 electron to form a chloride ion, Cl–, which is an anion.
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Question 233 Marks
What is the action of water on (a) sodium (b) magnesium, and (c) aluminium? Write equations of the chemical reactions involved.
Answer
  1. Sodium reacts vigorously with cold water forming sodium hydroxide and hydrogen gas.

$2\text{Na(s)}+2\text{H}_2\text{O(l)}\rightarrow2\text{NaOH(aq)}+\text{H}_2\text{(g)}+\text{Heat}$

  1. Magnesium reacts with hot water to from magnesium hydroxide and hydrogen.

$\text{Mg(s)}+2\text{H}_2\text{O(l)}\rightarrow\text{Mg(OH)}_2\text{(aq)}+\text{H}_2\text{(g)}$

  1. Aluminium reacts with steam to form aluminium oxide and hydrogen gas.

$2\text{Al(s)}+3\text{H}_2\text{O(g)}\rightarrow\text{Al}_2\text{O}_3\text{(s)}+3\text{H}_2\text{(g)}$

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Question 243 Marks
What is electroplating?
Answer
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.
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Question 253 Marks
What is calcination?
Answer
Calcination is derived from a Latin word calcinare which translates as “to burn lime”. It is the process of converting an ore into its oxide by heating strongly, below its melting point either in a limited supply or in absence of air. This method is commonly used for converting carbonates and hydroxides to their respective oxides. During calcination, moisture and volatile impurities are also removed.
For example: Calcium carbonate is converted into calcium oxide by calcination.
 CaCO3 → CaO + CO2
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Question 263 Marks
What is a thermite reaction? Explain with the help of an equation. State one use of this reaction.
Answer
The reduction of a metal oxide to form metal by using aluminium powder as a reducing agent is called a thermite reaction.

This property of reduction by aluminium is made use of in thermite welding for joining the broken pieces of heavy iron objects like girders etc.

A mixture of Iron (III) oxide and aluminium powder is ignited with a burning magnesium ribbon. Aluminium reduces iron oxide to produce iron metal with the evolution of a lot of heat. Due to this heat, iron metal is produced in the molten state.

This molten iron is then poured between the broken iron pieces to weld them (to join them).

$\text{Fe}_2\text{O}_3(\text{s})+2\text{Al(s)}\rightarrow2\text{Fe(l)}+\text{Al}_2\text{O}_3\text{(s)}+\text{Heat}$

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Question 273 Marks
What do you mean by ionic bond?
Answer
A chemical bond in which one atom loses an electron to form a positive ion and the other atom gains an electron to form a negative ion. Two-element compounds are usually ionic one element is a metal and the other is a non-metal. for example as in the formation of sodium chloride.
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Question 283 Marks
What are noble gases? What is the characteristic of the electronic configuration of noble gases?
Answer
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.
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Question 293 Marks
Using electron-dot diagrams which show only the outermost shell electrons, show how a molecule of oxygen, O2, is formed from two oxygen atoms. What name is given to this type of bonding? (At. No. of oxygen = 8)
Answer
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Question 303 Marks
Using electron-dot diagrams which show only the outermost shell electrons, show how a molecule of nitrogen, N, is formed from two nitrogen atoms. What name is given to this type of bonding? (Atomic number of nitrogen is 7)
Answer
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.
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Question 313 Marks
Two ores A and B were taken. On heating ore A gives CO2 whereas, ore B gives SO2. What steps will you take to convert them into metals?
Answer
Since the ore ‘A’ of the metal gives CO2 upon heating, it is some metal carbonate (MCO3). It can be converted to the metallic form as follows:

Calcination:

$\text{MCO}_3\text{(s)}\xrightarrow{\text{heat}}\text{MO(s)}+\text{CO}_2\text{(g)}$

Smelting:

$\text{MO}\text{(s)} +\text{C(s)}\xrightarrow{\text{heat}}\text{M(s)}+\text{CO}\text{(g)}\\ \ \ \ \ \ \ \ \ \ \ \ \ \ \text{(coke)}$

Since the ore ‘Y’ of the metal gives SO2 upon heating, it can be some metal sulphide (MS). It can be converted to the metallic form as follows:

Roasting:

$2\text{MS}\text{(s)}+3\text{O}_2\text{(g)}\rightarrow2\text{MO(s)}+2\text{SO}_2\text{(g)}$

Reduction:

$\text{MO}\text{(s)}+\text{C}\text{(s)}\rightarrow\text{M(s)}+\text{CO}\text{(g)}\\ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \text{(coke)}$

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Question 323 Marks
The electronic configurations of three elements X, Y and Z are as follows:

X 2, 4

Y 2, 1

Z 2, 1

  1. Which two elements will combine to form an ionic compound?
  2. Which two elements will react to form a covalent compound?

Give reasons for your choice.

Answer
  1. Y and Z will form an ionic compound because an ionic bond is formed when one of the atoms can donate electrons to achieve the inert gas configuration, and the other atom needs electrons to achieve the inert gas configuration. Since Y has 7 and Z has 1 electron in their outermost shell, they would form an ionic bond.
  2. X and Y will react to form a covalent compound because a covalent bond is formed when both the reacting atoms need electrons to achieve the inert gas electron arrangement.
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Question 333 Marks
The electronic configurations of three elements A, B and C are as follows:
A 2, 8, 1
B 2, 8, 7
C 2, 4
  1. Which of these elements is a metal?
  2. Which of these elements are non-metals?
  3. Which two elements will combine to form an ionic bond?
  4. Which two elements will combine to form a covalent bond?
  5. Which element will form an anion of valency 1?
Answer
  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.
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Question 343 Marks
The electronic configurations of four particles A, B, C and D are given below:
A 2, 8, 8
B 2, 8, 2
C 2, 6
D 2, 8
Which electronic configuration represents:
  1. Magnesium atom?
  2. Oxygen atom?
  3. Sodium ion?
  4. Chloride ion?
Answer
  1. B : Magnesium atom (At. no. = 12)
  2. C : Oxygen atom (At. no. = 8)
  3. D : Sodium ion (E.C = 2, 8)
  4. A : Chloride ion (E.C = 2, 8, 8)
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Question 353 Marks
Suppose you have to extract metal M from its enriched sulphide ore. If M is in the middle of the reactivity series, write various steps used in extracting this metal.
Answer
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.
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Question 363 Marks
State which of the following reactions will take place or which will not, giving a suitable reason for each?

$\text{Zn(s)}+\text{CuSO}_4(\text{aq})\rightarrow\text{ZnSO}_4(\text{aq})+\text{Cu(s)}$

$\text{Fe(s)}+\text{ZnSO}_4(\text{aq})\rightarrow\text{FeSO}_4(\text{aq})+\text{Zn(s)}$

Answer
As Zn is more reactive than copper it displaces copper from copper sulphate solution. So first reaction is possible.
In the second reaction iron is less reactive than zinc , it does not displace zinc from zinc sulphate solution.
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Question 373 Marks
State two ways to prevent the rusting of iron.
Answer
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.
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Question 383 Marks
State any three differences between the physical properties of metals and non-metals.
Answer
Difference between metals and non-metals:

Metals

  1. Metals are malleable i.e. they can be beaten into thin sheets with a hammer.
  2. Metals are ductile i.e. they can be drawn into thin wires.
  3. Metals are good conductors of heat and electricity.

Non-metals

  1. Non-metals are non-malleable i.e. they cannot be beaten into thin sheets with a hammer.
  2. Non-metals are non-ductile i.e. they cannot be drawn into thin wires.
  3. Non-metals are bad conductors of heat and electricity.
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Question 393 Marks
Samples of four metals A, B, C and D were taken and added to the following solution one by one. The results obtained have been tabulated as follows.
MetalIron (II) sulphateCopper (II)sulphateZincsulphateSilver nitrate
ANo reactionDisplacement----------
BDisplacement-----No reaction-----
CNo reactionNo reactionNo reactionDisplacement
DNo reactionNo reactionNo reactionNo reaction
Use the Table above to answer the following questions about metals A, B, C and D.
  1. Which is the most reactive metal?
  2. What would you observe if B is added to a solution of Copper(II) sulphate?
  3. Arrange the metals A, B, C and D in the order of decreasing reactivity.
Answer
  1. B is the most reactive metal.
  2. If B is added to a solution of copper (II) sulphate, displacement reaction will take place. Blue colour of copper sulphate will fade and red –brown copper will settle down.
  3. The decreasing order of reactivity is:

B> A> C >D

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Question 403 Marks
Pratyush took sulphur powder on a spatula and heated it. He collected the gas evolved by inverting a test tube over it, as shown in figure below.
  1. What will be the action of gas on:
  1. Dry litmus paper?
  2. Moist litmus paper?
  1. Write a balanced chemical equation for the reaction taking place.
Answer
  1. When sulphur is brunt in air then sulphur dioxide gas is formed.
  1. Sulphur dioxide gas has no action on dry litmus paper.
  2. Sulphur dioxide gas turns moist blue litmus paper to red.
  1. S(s) + O2(g) → SO2(g)
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Question 423 Marks
  1. Write electron-dot structures for magnesium and oxygen.
  2. Show the formation of MgO by the transfer of electrons.
  3. What are the ions present in this compound?
Answer
  1. Magnesium
  1. Formation of MgO
  1. Both positive and negative ions i.e. Mg2+ and O2- respectively.
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Question 433 Marks
  1. Name a metal for each case:
  1. It does not react with cold as well as hot water but reacts with steam.
  2. It does not react with any physical state of water?
  1. When calcium metal is added to water, the gas evolved does not catch fire but the same gas evolved on adding sodium metal to water catches fire. Why is it so?
Answer
  1.  
  1. Aluminium does not react with cold or hot water but it reacts with steam.
  2. Gold does not react with any physical state of water.
  1. Sodium is more reactive than calcium. The reaction between sodium and water produces a large amount of heat, which causes the evolved hydrogen to burn and catch fire. But in the reaction between calcium and water, no heat is produced and hence the evolved hydrogen does not catch fire.
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Question 443 Marks
  1. Give the names and formulae of one metal chloride and one non-metal chloride.
  2. State an important property in which these metal chloride and non-metal chloride differ.
  3. Why do they differ in this property?
Answer
  1. Sodium chloride is a metal chloride and its formula is NaCl.
    Hydrogen chloride is a non-metal chloride and its formula is HCl.
  2.  Metal chlorides are ionic chlorides, which are electrolytes that can conduct electricity. However, non-metal chlorides are covalent chlorides, which are non-electrolytes that do not conduct electricity.
  3. They differ in this property because of the bonding in the chlorides. Metal chlorides have ionic bonds but non-metal chlorides have covalent bonds.
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Question 453 Marks
Of the three metals X, Y and Z. X reacts with cold water, Y with hot water and Z with steam only. Identify X, Y and Z and also arrange them in order of increasing reactivity.
Answer
X is sodium, Y is magnesium and Z is iron.
2Na + 2H2O → 2NaOH + H2
Mg + 2H2O → Mg(OH)2 + H2
3Fe + 4H2O → Fe3O4 + 4H2
Their sequence in reactivity series is as follows:
Fe < Mg < Na.
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Question 463 Marks
Name two metals which react violently with cold water. Write any three observations you would make when such a metal is dropped into water. How would you identify the gas evolved, if any, during the reaction?
Answer
Sodium and potassium metals react violently with cold water Observations:
  1. Metal starts moving over the surface of water making a hissing sound.
  2. Metal starts reacting with water causing little explosions.
  3. Soon the metal catches fire and starts burning.
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Question 473 Marks
Metals are said to be shiny. Why do metals generally appear to be dull ? How can their brightness be restored?
Answer
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.
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Question 483 Marks
Metallic oxides of zinc, magnesium and copper were heated with the following metals.
MetalZincMagnesiumCopper
Zinc oxide------------
Magnesium oxide------------
Copper oxide------------
In which cases will you find displacement reactions taking place?
Answer
MetalZincMagnesiumCopper
Zinc oxideNo reactionDisplacementNo reaction
MagnesiumoxideNo reactionNo reactionNo reaction
CopperoxideDisplacementDisplacementNo reaction
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Question 493 Marks
List three properties of sodium in which it differs from the general physical properties of most of the metals.
Answer
Three properties in which it differ from the general properties of metals are as follow :
  1. Sodium is soft, i.e. it can be cut with the help of knife.
  2. It is non-sonorous metal which means it does not make sound on being hit by hard object.
  3. Its melting point and boiling point are quite low.
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Question 503 Marks
Iqbal treated a lustrous, divalent element M with sodium hydroxide. He observed the formation of bubbles in reaction mixture. He made the same observations when this element was treated with hydrochloric acid. Suggest how can he identify the produced gas. Write chemical equations for both the reactions.
Answer
The divalent element M is a metal. It reacts with both sodium hydroxide (alkali) and dilute hydrochloric acid to evolve hydrogen gas.
M(s) + 2NaOH(aq) → Na2MO2(aq) + H2(g)
M(s) + 2HCl(aq) → MCl2(aq) + H2(g)
The gas burns with a pop sound when a burning match stick is brought near it.
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