CBSE Class 10 Science HOTs Metals and Non Metals Set 04

Question. Which of the following ore is concentrated by Froth floatation process?
(a) \( ZnCO_3 \)
(b) ZnO
(c) ZnS
(d) \( Na_2S \)
Answer: (c) ZnS

Question. In extraction of copper, the flux used is
(a) CaO
(b) \( SiO_2 \)
(c) FeO
(d) \( FeSiO_3 \)
Answer: (b) \( SiO_2 \)

Question. \( Cu_2S + 3Cu_2O \rightarrow 6Cu + SO_2 \). The above process is
(a) auto-reduction
(b) Roasting
(c) electrolytic reduction
(d) None of the options
Answer: (a) auto-reduction

Question. Which of the following is not an ionic compound?
(a) \( KCl \)
(b) \( MgCl_2 \)
(c) \( CCl_4 \)
(d) \( NaCl \)
Answer: (c) \( CCl_4 \)

Question. Which option gives the process of extraction of mercury from its ore cinnabar? 
(a) Cooling cinnabar in the presence of excess air.
(b) Cooling cinnabar to convert into HgO and then heating it.
(c) Heating cinnabar in air to convert into HgO and then heating it again.
(d) Heating cinnabar in limited air and then adding to small amount of water.
Answer: (c) Heating cinnabar in air to convert into HgO and then heating it again.

Question. A researcher conducts an experiment to obtain Zn from its ore. Which option gives the process that the researcher must perform? 
(a) Converting metal sulphide into metal oxides then using carbon to reduce it to obtain pure metal.
(b) Metal oxide into metal sulphide and reducing with C to get pure metal.
(c) Converting metal oxide into metal carbonate then reducing with C to get pure metal.
(d) Metal sulphide into metal carbonate and then heating to get pure metal.
Answer: (a) Converting metal sulphide into metal oxides then using carbon to reduce it to obtain pure metal.

Question. In extraction of iron, the flux used is
(a) CaO
(b) \( SiO_2 \)
(c) FeO
(d) \( FeSiO_3 \)
Answer: (a) CaO

Very Short Answer Type Questions 

Question. Name a metal/non-metal: 
(i) Which makes iron hard and strong?
(ii) Which is alloyed with any other metal to make an amalgam?
(iii) Which is used to galvanise iron articles?
(iv) Whose articles when exposed to air form a black coating?
Answer: (i) Carbon (ii) Mercury (iii) Zinc (iv) Silver

Question. Which one of the methods given in Column I are used for extraction of each of the metals given in Column II.
| Column I | Column II |
| :--- | :--- |
| (i) Electrolytic reduction | Al, Na |
| (ii) Reduction with carbon | Zn, Fe, Sn |
| (iii) Reduction with Al | Mn |
Answer: (i) Electrolytic reduction is used in case of Al, Na.
(ii) Reduction with carbon is done in case of Zn, Fe, Sn.
(iii) Reduction with Al is carried out in case of Mn.

Question. What is an alloy? State the constituents of solder. Which property of solder makes it suitable for welding electrical wires?
Answer: Alloy is a homogeneous mixture of two or more metals. One of them can be a non-metal also. Solder consists of lead and tin, it has low melting point which makes it suitable for soldering electric wires.

Question. What is 24 carat gold? How will you convert it into 18 carat gold?
Answer: 24 carat gold is pure gold. It is converted into 18 carat gold by adding 6 parts of copper to 18 parts of gold, i.e., 75% Au and 25% Cu.

Short Answer Type Questions 

Question. An ore on heating in air produces sulphur dioxide. Which process would you suggest for its concentration? Describe briefly any two steps involved in the conversion of this concentrated ore into related metal.
Answer: It is concentrated by froth-floatation process.
(i) Roasting: The concentrated sulphide ore is heated strongly in the presence of oxygen to convert it into its oxide.
\( 2ZnS(s) + 3O_2(g) \rightarrow 2ZnO(s) + 2SO_{2(g)} \)
(ii) Reduction: This oxide of metal is reduced with suitable reducing agent to get free metal.
\( ZnO(s) + C(s) \xrightarrow{heat} Zn(s) + CO_{(g)} \)

Question. (a) What is reactivity series? How does the reactivity series help in predicting the relative activity of various metal?
(b) Suggest different chemical processes used for obtaining a metal from its oxides of metals in the middle and top of reactivity series. Support your answer with one example. 
Answer: (a) The series of metals in decreasing order of reactivity is called reactivity series of metals. The metals at the top are most reactive and metals at the bottom are least reactive.
(b) The metals in the middle of reactivity series are obtained from their ores by chemical reduction with suitable reducing agent, e.g. \( ZnO + C \rightarrow Zn + CO \). The metals at the top of series are obtained by electrolytic reduction of their molten ore.
\( Al_2O_3 \xrightarrow{electrolysis} 2Al^{3+} + 3O^{2-} \)
At cathode: \( 2Al^{3+} + 6e^- \rightarrow 2Al \)
At anode: \( O^{2-} - 2e^- \rightarrow O \); \( O + O \rightarrow O_2 \)

Question. What is cinnabar? How is metal extracted from cinnabar? Explain briefly. 
Answer: Cinnabar is HgS. Mercury is obtained by roasting cinnabar. HgO formed is thermally unstable and gives mercury.
\( 2HgS(s) + 3O_{2(g)} \rightarrow 2HgO(s) + 2SO_{2(g)} \)
\( 2HgO(s) \xrightarrow{heat} 2Hg(l) + O_{2(g)} \) 
Mercury can be purified by distillation.

Question. What is purpose of making alloys?
Answer: Purpose of Making Alloy are as follows:
(i) Alloys do not get corroded or corroded to very less extent.
(ii) They are harder and stronger than pure metal, e.g., gold mixed with copper is harder than pure gold.
(iii) They have less conductance than pure metals, e.g., copper is good conductor of heat and electricity whereas brass and bronze are not good conductors.
(iv) Some alloys have lower melting point than pure metals, e.g., solder is an alloy of lead and tin which has lower melting point than each of the metals. It is used for soldering of metals.

Long Answer Type Questions 

Question. (a) Differentiate between roasting and calcination. Explain the two with the help of suitable chemical equations. How is zinc extracted from its ore?
(b) Name two metals that can be used to reduce metal oxides to metals. 
Answer: (a)
| Calcination | Roasting |
| It is a process in which carbonate ore is heated in absence of air to form oxide. | It is process in which sulphide ore is heated in presence of oxygen to convert into oxide. |
| \( ZnCO_{3(s)} \xrightarrow{heat} ZnO(s) + CO_{2(g)} \) | \( 2ZnS + 3O_2 \rightarrow 2ZnO + 2SO_2 \) 
By reduction process, Zn can be extracted from its ore. Reduction: \( ZnO + C \rightarrow Zn + CO \).
(b) Aluminium, Magnesium.

PRACTICE QUESTIONS

Question. Bronze is an alloy of
(a) Copper and zinc
(b) Aluminium and tin
(c) Copper, tin, zinc
(d) Copper and tin 
Answer: (d) Copper and tin

Question. Which of the following is incorrect description of the process: 
(a) The impure metal from anode dissolves in electrolyte.
(b) The pure metal from the electrolyte deposits at cathode.
(c) Insoluble impurities settle at the bottom of anode.
(d) On passing electric current through the electrolyte, the pure metal from anode dissolves into electrolyte. 
Answer: (d) On passing electric current through the electrolyte, the pure metal from anode dissolves into electrolyte.

Question. Mention the names of the metals for the following: (a) Two metals which are alloyed with iron to make stainless steel. (b) Two metals which are used to make jewellery. 
Answer: (a) Chromium and Nickel. (b) Gold and Silver.

Question. A student has been collecting silver coins and copper coins. One day she observed a black coating on silver coins and green coating on copper coins. Give the chemical name of black and green coating. How are they formed?
Answer: Black coating: Silver sulphide (\( Ag_2S \)). Green coating: Basic copper carbonate (\( CuCO_3 \cdot Cu(OH)_2 \)). They are formed by corrosion of metals in air.

Question. (a) State the electron-dot structure for calcium and sulphur.
(b) Show the formation of CaS by the transfer of electrons.
(c) Name the ions present in this compound CaS. [Atomic number of Ca = 20, O = 16.] 
Answer: (a) Ca: (2, 8, 8, 2); S: (2, 8, 6).
(b) Ca donates two electrons to S atom, forming \( Ca^{2+} S^{2-} \).
(c) Ions are \( Ca^{2+} \) and \( S^{2-} \).

Question. (a) Explain the formation of ionic compound CaO with electron dot structure. Atomic number of calcium and oxygen are 20 and 8 respectively. (b) Name the constituent metals of bronze. 
Answer: (a) Ca: (2, 8, 8, 2) loses 2 electrons to Oxygen: (2, 6) forming \( Ca^{2+} O^{2-} \).
(b) Copper and Tin.

Question. Suggest a method of reduction for the following metals during their metallurgical processes: (a) metal ‘A’ which is one of the last second or third position in the reactivity. (b) metal ‘B’ which gives vigorous reaction even with water and air. (c) metal ‘C’ which is kept in the middle of activity series.
Answer: (a) Self-reduction or heating alone. (b) Electrolytic reduction. (c) Chemical reduction with carbon or Al.

Question. (a) Carbon cannot be used as reducing agent to obtain Mg from MgO. Why? (b) How is sodium obtained from molten sodium chloride? Give equation of the reactions. (c) How is copper obtained from its sulphide ore? Give equations of the reactions.
Answer: (a) Magnesium has a higher affinity for oxygen than carbon. (b) By electrolysis of molten NaCl. \( 2NaCl \rightarrow 2Na + Cl_2 \). (c) By roasting and self-reduction. \( 2Cu_2S + 3O_2 \rightarrow 2Cu_2O + 2SO_2 \); \( 2Cu_2O + Cu_2S \rightarrow 6Cu + SO_2 \).

Question. (a) Define corrosion. (b) What is corrosion of iron called? (c) How will you recognise the corrosion of silver? (d) Why corrosion of iron is a serious problem? (e) How can we prevent corrosion of iron?
Answer: (a) Slow eating away of metals by air, moisture or chemicals. (b) Rusting. (c) Formation of black silver sulphide coating. (d) It weakens iron structures and causes huge economic loss. (e) Painting, galvanising, alloying.

INTEGRATED (MIXED) QUESTIONS

Question. The way, metals like sodium, magnesium and iron react with air and water is an indication of their relative positions in the ‘reactivity series’. Is this statement true ? Justify your answer with examples. (2 Marks)
Answer: Yes, it is true. Sodium reacts with cold water, magnesium with hot water, and iron only with steam, indicating decreasing reactivity.

Question. Explain the following statements:
(a) Most metal oxides are insoluble in water but some of these dissolve in water. What are these oxides and their solutions in water called?
(b) At ordinary temperature the surface of metals such as magnesium, aluminium, zinc, etc. is covered with a thin layer. What is the composition of this layer? State its importance.
(c) Some alkali metals can be cut with a knife. 
Answer: (a) Alkalis; e.g. NaOH, KOH. (b) Metal oxide layer. It protects the metal from further oxidation. (c) Alkali metals like Na, K are soft due to weak metallic bonding.

Question. (a) Give reason for the following: 
(i) Metals can be given different shapes according to our needs.
(ii) Hydrogen is not evolved when a metal reacts with dilute nitric acid.
(b) Write chemical equations that shows zinc oxide reacts with acid as well as base.
Answer: (a) (i) Malleability and ductility. (ii) \( HNO_3 \) oxidises \( H_2 \) to \( H_2O \). (b) \( ZnO + 2HCl \rightarrow ZnCl_2 + H_2O \); \( ZnO + 2NaOH \rightarrow Na_2ZnO_2 + H_2O \).

Question. (a) Write one example of each of 
(i) A metal which is so soft that, it can be cut with knife and a non-metal which is the hardest sustance.
(ii) A metal and a non-metal which exist as liquid at room temperature.
(b) Using the electronic configurations, explain how magnesium atom combines with oxygen atom to form magnesium oxide by transfer of electrons.
Answer: (a) (i) Sodium, Diamond. (ii) Mercury, Bromine. (b) Mg: (2, 8, 2) transfers 2 electrons to O: (2, 6) forming \( Mg^{2+} O^{2-} \).

Question. (a) Elements magnesium and oxygen respectively belong to group 2 and group 16 of the Modern Periodic Table. If the atomic numbers of magnesium and oxygen are 12 and 8 respectively, explain their bonding.
Answer: Mg has 2 valence electrons, O has 6. Mg transfers 2 electrons to O to form an ionic bond.

ASSERTION AND REASON QUESTIONS

Direction: In the following Questions, the Assertion and Reason have been put forward. Read the statements carefully and choose the correct alternative from the following:
(a) Both the Assertion and the Reason are correct and the Reason is the correct explanation of the Assertion.
(b) The Assertion and the Reason are correct but the Reason is not the correct explanation of the Assertion.
(c) Assertion is true but the Reason is false.
(d) The statement of the Assertion is false but the Reason is true.

Question. Assertion: Sodium oxide is an amphoteric oxide.
Reason: Those oxides which react with acid as well as base are amphoteric oxides. 
(a) A
(b) B
(c) C
(d) D

Answer: (d) The statement of the Assertion is false but the Reason is true.

Question. Assertion: Nitrogen is a non-metal.
Reason: Nitrogen has 5 valence electrons.
(a) A
(b) B
(c) C
(d) D

Answer: (b) Both the Assertion and the Reason are correct but the Reason is not the correct explanation of the Assertion.

Question. Assertion: Copper does not reacts with dil. \( H_2SO_4 \).
Reason: Copper is more reactive than hydrogen
(a) A
(b) B
(c) C
(d) D

Answer: (c) Assertion is true but the Reason is false.

Question. Assertion: Highly reactive metals are obtained by electrolytic reduction of their molten ore.
Reason: Highly reactive metals can be extracted by chemical reduction.
(a) A
(b) B
(c) C
(d) D

Answer: (c) Assertion is true but the Reason is false.

Question. Assertion: Silver becomes black in colour when exposed to atmosphere.
Reason: Silver reacts with \( H_2S \) gas to form \( Ag_2S \) which is black in colour.
(a) A
(b) B
(c) C
(d) D

Answer: (a) Both the Assertion and the Reason are correct and the Reason is the correct explanation of the Assertion.

Question. Assertion: The metals and alloys are good conductors of electricity.
Reason: Bronze is an alloy of copper and tin and it is not good conductor of electricity.
(a) A
(b) B
(c) C
(d) D

Answer: (b) Both the Assertion and the Reason are correct but the Reason is not the correct explanation of the Assertion.

Question. Assertion: If \( Na_2O \) reacts with \( HCl \), it will form \( NaCl \) and \( H_2O \).
Reason: Sodium reacts with air to form sodium oxide \( (Na_2O) \).
(a) A
(b) B
(c) C
(d) D

Answer: (b) Both the Assertion and the Reason are correct but the Reason is not the correct explanation of the Assertion.

Question. Assertion: Metals are reducing agents.
Reason: Metals form positive ions by loss of electrons.
(a) A
(b) B
(c) C
(d) D

Answer: (a) Both the Assertion and the Reason are correct and the Reason is the correct explanation of the Assertion.

Question. Assertion: Lead reacts with \( H_2SO_4 \) to form lead sulphate and further reaction stops.
Reason: Lead sulphate is insoluble in water and forms a coating over lead metal preventing further reaction.
(a) A
(b) B
(c) C
(d) D

Answer: (a) Both the Assertion and the Reason are correct and the Reason is the correct explanation of the Assertion.

Question. Assertion: Sodium chloride has melting point above \( 1000^\circ C \).
Reason: Sodium chloride conducts electricity in solid state.
(a) A
(b) B
(c) C
(d) D

Answer: (c) Assertion is true but the Reason is false.

Question. Assertion: The colour of an aqueous solution of copper sulphate turns colourless when a piece of lead is added to it.
Reason: Lead is more reactive than copper and hence displaces copper from its salt solution.
(a) A
(b) B
(c) C
(d) D

Answer: (a) Both the Assertion and the Reason are correct and the Reason is the correct explanation of the Assertion.

Question. Assertion: K is more reactive than Na.
Reason: K is smaller is size than Na.
(a) A
(b) B
(c) C
(d) D

Answer: (c) Assertion is true but the Reason is false.

Question. Assertion: Certain elements show properties of both metals and non-metals and are called metalloids.
Reason: Silicon and germanium are metalloids as they resemble with metals as well as non-metals.
(a) A
(b) B
(c) C
(d) D

Answer: (a) Both the Assertion and the Reason are correct and the Reason is the correct explanation of the Assertion.

Question. Assertion: \( MgCl_2 \) is covalent compound.
Reason: Metals and non-metals react by mutual transfer of electrons.
(a) A
(b) B
(c) C
(d) D

Answer: (d) The statement of the Assertion is false but the Reason is true.

Question. Assertion: Sodium is less reactive than lead.
Reason: Sodium is kept in kerosene.
(a) A
(b) B
(c) C
(d) D

Answer: (d) The statement of the Assertion is false but the Reason is true.

Question. Assertion: Na, Ca, Mg are obtained by electrolysis of their molten oxides.
Reason: These metals have more affinity for oxygen than carbon. 
(a) A
(b) B
(c) C
(d) D

Answer: (a) Both the Assertion and the Reason are correct and the Reason is the correct explanation of the Assertion.