CBSE Class 10 Science Metals and Non metals VBQs Set 02

CASE-BASED QUESTIONS

Elements are classified into metals, non-metals and metalloids. Metals are lustrous, malleable, ductile and good conductors of heat and electricity, mostly solids, form positive ions and basic oxides. Non-metals are non-lustrous, brittle, exist as solids, liquids and gases, non-conductor of heat and electricity, form negative ions and acidic oxides mostly. Some metals form amphoteric oxides and some non-metals form neutral oxides. A more reactive metal can displace less reactive metal from its salt solution. Some less reactive metals occur in free state. Most of metals occur in combined state in form of ores. Carbonates ores are converted into oxides by calcination and sulphide ores are roasted in presence of oxygen to form oxides. Oxides are reduced with suitable reducing agent to get free metal. Metals of middle reactivity series are obtained from their oxides by reduction with Al, Mg. Most reactive metals are obtained by electrolytic reduction of their molten ores. Impure metals are refined by suitable methods. Metals form ionic compounds with non-metals. Ionic compounds are soluble in water, high melting solids, conduct electricity in molten state and in aqueous solution.

Question. Out of elements from atomic number 1 to 20, name metalloids.

Answer: Boron \( (B) \) and Silicon \( (Si) \).

Question. X has atomic number (20) and Y has 17. What is formula of compound formed?

Answer: Element X (Calcium, Z=20) has valency 2 and Y (Chlorine, Z=17) has valency 1. The formula is \( XY_2 \) (specifically \( CaCl_2 \)).

Question. What happens when zinc carbonate is heated in absence of air? Name the process.

Answer: Zinc oxide and carbon dioxide are formed. The process is called calcination.
\( ZnCO_3 \xrightarrow{\Delta} ZnO + CO_2 \)

Question. What happens when Zn metal reacts with \( FeSO_4(aq) \)? Write chemical equation.

Answer: Zinc displaces iron from iron sulphate solution because zinc is more reactive than iron.
\( Zn(s) + FeSO_4(aq) \rightarrow ZnSO_4(aq) + Fe(s) \)

Pure metals are usually too soft and weak for most uses. In pure metals the atoms are arranged orderly in layers. When force is applies to the metal, the layers of metal atoms can slide over one another. To improve the strength and hardness of metals, atoms of another element can be added usually in small amounts which prevents atoms of the metal from sliding over one another, making the metals stronger and harder and less likely to get its shape distorted. The final product is an alloy of metal, e.g. ornaments are made up of 22 carat gold in which copper is added to gold. Alloy is a homogeneous mixture of two or more metals. One of them can be non-metal also, e.g., steel is an alloy of Fe and carbon. Alloys are made so as to improve properties of metals. Amalgam is alloy of metal with mercury.

Question. What is composition of stainless steel?

Answer: Iron \( (Fe) \), Chromium \( (Cr) \), and Nickel \( (Ni) \).

Question. Which metal is present is solder, brass and bronze?

Answer:
• Solder: Lead and Tin.
• Brass: Copper and Zinc.
• Bronze: Copper and Tin.

Question. What is amalgam? Give an example.

Answer: Amalgam is an alloy of a metal with mercury. Example: Sodium amalgam \( (Na-Hg) \) or Zinc amalgam.

Question. Calculate the percentage of gold present in 22 carat gold.

Answer: Percentage of gold \( = \frac{22}{24} \times 100 \approx 91.67\% \).

A student, took four metals P, Q, R and S and carried out different experiments to study the properties of metals. Some of the observations were: 
• All metals could not be cut with knife except metal R.
• Metal P combined with oxygen to form an oxide \( M_2O_3 \) which reacted with both acids and bases.
• Reaction with water.
P – Did not react either with cold or hot water but reacted with steam.
Q – Reacted with hot water and the metal started floating.
R – Reacted violently with cold water.
S – Did not react with water at all.

Question. Identify metal Q out of Fe, Zn, K, Mg? Give reason.

Answer: Metal Q is Magnesium \( (Mg) \). Reason: It reacts with hot water to form magnesium hydroxide and hydrogen gas. The bubbles of hydrogen stick to its surface, causing it to float.

Question. Identify metal which forms amphoteric oxide.

Answer: Metal P is Aluminium \( (Al) \). It forms \( Al_2O_3 \), which is amphoteric.

Question. Arrange the metals in increasing order of reactivity. Give reason.

Answer: S < P < Q < R.
Reason: R reacts violently with cold water (most reactive), Q reacts with hot water, P reacts only with steam, and S does not react with water at all (least reactive).

Question. Which metal is kept in kerosene oil and why?

Answer: Metal R (Sodium or Potassium). It is highly reactive and reacts vigorously with oxygen and moisture in the air; hence it is stored in kerosene to prevent contact with air.

The activity series of metals is shown in the box. Study this table carefully and answer the questions based on this series and related studied concepts.
Reactivity Series: K, Na, Ca, Mg, Al, Zn, Fe, Pb, H, Cu, Ag, Au

Question. What happens when Ag metal is added to \( CuSO_4 \) solution?
Answer: No reaction occurs because silver (Ag) is less reactive than copper (Cu) and cannot displace it from its salt solution.

Question. Why does Au exist in free state?
Answer: Gold (Au) is at the bottom of the reactivity series, meaning it is highly unreactive. It does not react with atmospheric gases or moisture, thus it exists in its free (native) state.

Question. Can we store \( MgSO_4(aq) \) in a copper container? Give reason.
Answer: Yes, we can store \( MgSO_4(aq) \) in a copper container because copper is less reactive than magnesium and will not undergo a displacement reaction with magnesium sulphate.

Question. Which metals do not occur in free state and react with cold water? How are these extracted?
Answer: Highly reactive metals like Potassium (K) and Sodium (Na) do not occur in the free state and react vigorously with cold water. These are extracted by the electrolytic reduction of their molten chlorides.

Question. The following table gives the melting point of some metals. Study the table and answer the questions related to the table and related studied concepts.
Metals: Na (98°C), Ag (961.8°C), Cu (1085°C), Al (660.3°C), Zn (419.5°C), Au (1064°C), Sn (231.9°C), Hg (-38.83°C). (a) How are sodium and mercury refined? Why? (b) Name two metals purified by electrolytic refining. (c) In electrolytic refining of copper, name the cathode, anode and electrolyte used.
Answer: (a) Sodium is refined by electrolysis because it is highly reactive. Mercury is refined by distillation because it has a very low boiling point compared to its impurities. (b) Copper and Zinc are commonly purified by electrolytic refining. (c) In the electrolytic refining of copper:

• Cathode: A thin strip of pure copper.
• Anode: A thick block of impure copper.
• Electrolyte: An acidified solution of copper sulphate (\( CuSO_4 \)).

Question. Why is bauxite mixed with cryolite before electrolytic reduction in extraction of aluminium?
Answer: Cryolite (\( Na_3AlF_6 \)) is added to bauxite to lower the melting point of alumina (\( Al_2O_3 \)) from about 2323 K to 1173 K and to increase the electrical conductivity of the mixture.

Question. Almost all metals combine with oxygen to form metal oxides. Metal oxides are generally basic in nature. But some metals show both basic as well as acidic behavior. Different metals show different reactivities towards oxygen. Some react vigorously while some do not react at all. (a) What happens when copper is heated in air? Give the equation of the reaction involved. (b) Why are some metal oxides categorised as amphoteric? Give one example. (c) Complete the following reaction: (i) \( Na_2O(s) + H_2O(l) \rightarrow \) (ii) \( Al_2O_3(s) + 2NaOH \rightarrow \)
Answer: (a) When copper is heated in air, it reacts with oxygen to form a black layer of copper(II) oxide.
\( 2Cu(s) + O_2(g) \xrightarrow{Heat} 2CuO(s) \) (b) Metal oxides that react with both acids as well as bases to produce salts and water are called amphoteric oxides. Example: Aluminum oxide (\( Al_2O_3 \)) or Zinc oxide (\( ZnO \)). (c) (i) \( Na_2O(s) + H_2O(l) \rightarrow 2NaOH(aq) \)
(ii) \( Al_2O_3(s) + 2NaOH(aq) \rightarrow 2NaAlO_2(aq) + H_2O(l) \)

Question. On burning sulphur in oxygen a colourless gas is produced. (i) Write chemical equation for the reaction. (ii) Name the gas formed. (iii) State the nature of the gas. (iv) What will be action of this on dry litmus paper?
Answer: (i) \( S(s) + O_2(g) \rightarrow SO_2(g) \) (ii) The gas formed is sulphur dioxide. (iii) Sulphur dioxide is acidic in nature (it forms sulphurous acid when dissolved in water). (iv) It will have no action on dry litmus paper. Litmus paper must be moist to show the acidic nature.

Question. On the basis of reactivity metals are grouped into three categories: (i) Metals of low reactivity (ii) Metals of medium reactivity (iii) Metals of high reactivity. (a) Name the process of reduction used for a metal that gives vigorous reaction with air and water both. (b) Carbon cannot be used as a reducing agent to obtain aluminium from its oxide. Why? (c) Describe briefly the method to obtain mercury from cinnabar. Write the chemical equation for the reaction involved in the process.
Answer: (a) Electrolytic reduction is used for highly reactive metals. (b) Aluminum has a higher affinity for oxygen than carbon does, so carbon cannot reduce aluminum oxide to aluminum. (c) Cinnabar (\( HgS \)) is first heated in air (roasting) to convert it into mercuric oxide. On further heating, mercuric oxide is reduced to mercury metal.
\( 2HgS(s) + 3O_2(g) \xrightarrow{Heat} 2HgO(s) + 2SO_2(g) \)
\( 2HgO(s) \xrightarrow{Heat} 2Hg(l) + O_2(g) \)

Question. Differentiate between roasting and calcination giving chemical equation for each.
Answer:

• Roasting: Heating sulphide ores strongly in the presence of excess air to convert them into oxides.
  Example: \( 2ZnS + 3O_2 \xrightarrow{Heat} 2ZnO + 2SO_2 \)
• Calcination: Heating carbonate ores strongly in limited or no air to convert them into oxides.
  Example: \( ZnCO_3 \xrightarrow{Heat} ZnO + CO_2 \)

Question. The melting points and boiling points of some ionic compounds are given below: NaCl (MP: 1074K, BP: 1686K), LiCl (MP: 887K, BP: 1600K), CaCl2 (MP: 1045K, BP: 1900K), CaO (MP: 2850K, BP: 3120K), MgCl2 (MP: 981K, BP: 1685K). (a) Show the electron transfer in the formation of magnesium chloride. (b) List two properties of ionic compounds other than their high melting and boiling points. (c) While forming an ionic compound say sodium chloride how does sodium atom attain its stable configuration?
Answer: (a) Magnesium (2, 8, 2) loses two electrons to form \( Mg^{2+} \). Two chlorine atoms (2, 8, 7) each gain one electron to form \( Cl^- \) ions.
\( Mg \rightarrow Mg^{2+} + 2e^- \)
\( 2Cl + 2e^- \rightarrow 2Cl^- \)
(b) 1. They are generally hard and brittle solids. 2. They conduct electricity in molten or aqueous states but not in solid state. (c) Sodium (2, 8, 1) loses its one valence electron to attain the stable octet configuration of neon (2, 8), becoming a sodium cation (\( Na^+ \)).

Question. Give reasons: (i) Why do ionic compounds in the solid state not conduct electricity? (ii) What happens at the cathode when electricity is passed through an aqueous solution of sodium chloride?
Answer: (i) In the solid state, the ions are held together in fixed positions by strong electrostatic forces and are not free to move to conduct electricity. (ii) At the cathode, hydrogen gas is evolved because \( H^+ \) ions (from water) are more easily reduced than \( Na^+ \) ions.
\( 2H^+(aq) + 2e^- \rightarrow H_2(g) \)

QUESTIONS

Question. Give an example of a metal which: (i) is a liquid at room temperature. (ii) can be easily cut with a knife. (iii) is the best conductor of heat. (iv) is a poor conductor of heat.
Answer: (i) Mercury (ii) Sodium (or Potassium/Lithium) (iii) Silver (or Copper) (iv) Lead (or Mercury)

Question. Explain the meanings of malleable and ductile.
Answer: Malleable: The property of metals that allows them to be beaten into thin sheets. Gold and silver are the most malleable metals.
Ductile: The property of metals that allows them to be drawn into thin wires. Platinum, gold, and silver are among the most ductile metals.

Question. Why is sodium kept immersed in kerosene oil?
Answer: Sodium is a very reactive metal. It reacts vigorously and explosively with oxygen in the air and with water at room temperature, which can cause it to catch fire. To prevent accidental contact and fire, it is stored immersed in kerosene oil.

Question. Write equations for the reactions of: (i) iron with steam. (ii) calcium and potassium with water.
Answer: (i) \( 3Fe(s) + 4H_2O(g) \rightarrow Fe_3O_4(s) + 4H_2(g) \) (ii) \( Ca(s) + 2H_2O(l) \rightarrow Ca(OH)_2(aq) + H_2(g) + Heat \)
\( 2K(s) + 2H_2O(l) \rightarrow 2KOH(aq) + H_2(g) + Heat \)

Question. Samples of four metals A, B, C and D were taken and added to the following solutions one by one. The results obtained have been tabulated as follows:
- Metal A: Iron(II) sulphate (No reaction), Copper(II) sulphate (Displacement).
- Metal B: Iron(II) sulphate (Displacement), Zinc sulphate (No reaction).
- Metal C: Iron(II) sulphate (No reaction), Copper(II) sulphate (No reaction), Zinc sulphate (No reaction), Silver nitrate (Displacement).
- Metal D: Iron(II) sulphate (No reaction), Copper(II) sulphate (No reaction), Zinc sulphate (No reaction), Silver nitrate (No reaction). Use the Table above to answer the following questions about metals A, B, C and D. (i) Which is the most reactive metal? (ii) What would you observe if B is added to a solution of copper (II) sulphate? (iii) Arrange the metals A, B, C and D in the order of decreasing reactivity.
Answer: (i) Metal B is the most reactive because it can displace iron from its sulphate solution (none of the others can). (ii) If B is added to copper(II) sulphate, a displacement reaction will occur because B is more reactive than iron, and iron is more reactive than copper. Thus, B will displace copper from the solution. (iii) Decreasing order: B > A > C > D.
Reasoning: B displaces Fe. A does not displace Fe but displaces Cu. C does not displace Fe, Cu, or Zn but displaces Ag. D does not displace any.

Question. Which gas is produced when dilute hydrochloric acid is added to a reactive metal? Write the chemical reaction when iron reacts with dilute \( H_2SO_4 \).
Answer: Hydrogen gas is produced.
Reaction: \( Fe(s) + H_2SO_4(dil.) \rightarrow FeSO_4(aq) + H_2(g) \)

Question. What would you observe when zinc is added to a solution of iron(II) sulphate? Write the chemical reaction that takes place.
Answer: Zinc is more reactive than iron, so it displaces iron from the greenish iron(II) sulphate solution, making it a colorless zinc sulphate solution, and grey iron metal is deposited.
\( Zn(s) + FeSO_4(aq) \rightarrow ZnSO_4(aq) + Fe(s) \)

Question. (i) Write the electron-dot structures for sodium, oxygen and magnesium. (ii) Show the formation of \( Na_2O \) and MgO by the transfer of electrons. (iii) What are the ions present in these compounds?
Answer: (i) Sodium (2, 8, 1) dot structure: \( Na \cdot \). Oxygen (2, 6) dot structure: \( : \ddot{O} : \). Magnesium (2, 8, 2) dot structure: \( Mg : \). (ii) Formation of \( Na_2O \): Two sodium atoms each lose one electron to form two \( Na^+ \) ions. One oxygen atom gains these two electrons to form an \( O^{2-} \) ion.
\( 2Na \rightarrow 2Na^+ + 2e^- \)
\( O + 2e^- \rightarrow O^{2-} \)
Formation of MgO: One magnesium atom loses two electrons to form \( Mg^{2+} \). One oxygen atom gains these two electrons to form \( O^{2-} \).
\( Mg \rightarrow Mg^{2+} + 2e^- \)
\( O + 2e^- \rightarrow O^{2-} \) (iii) In \( Na_2O \), the ions are \( Na^+ \) and \( O^{2-} \). In MgO, the ions are \( Mg^{2+} \) and \( O^{2-} \).

Question. Why do ionic compounds have high melting points?
Answer: Ionic compounds have high melting points because they consist of a giant lattice of oppositely charged ions held together by very strong electrostatic forces of attraction. A large amount of energy is required to break these strong bonds.

Question. Define the following terms. (i) Mineral (ii) Ore (iii) Gangue
Answer: (i) Mineral: Naturally occurring inorganic substances found in the earth's crust which contain metals or their compounds. (ii) Ore: A mineral from which one or more metals can be extracted profitably and easily. (iii) Gangue: The unwanted earthy or rocky impurities (like sand, clay, etc.) present in an ore mined from the earth.

Question. Name two metals which are found in nature in the free state.
Answer: The metals present at the bottom of the reactivity series are mostly found in free state. For example: gold, silver, and platinum. (any two)

Question. What chemical process is used for obtaining a metal from its oxide?
Answer: The chemical process used for obtaining a metal from its oxide is reduction. There are mainly three different methods of reduction:
(i) By heating
(ii) By using carbon
(iii) By using aluminium, calcium, sodium etc. as reducing agents.

Question. Metallic oxides of zinc, magnesium and copper were heated with the following metals.
Metal: Zinc, Magnesium, Copper
Zinc oxide: —, —, —
Magnesium oxide: —, —, —
Copper oxide: —, —, —
In which cases will you find displacement reactions taking place?
Answer:
- Zinc oxide: No reaction with Zinc, Displacement with Magnesium, No reaction with Copper.
- Magnesium oxide: No reaction with Zinc, No reaction with Magnesium, No reaction with Copper.
- Copper oxide: Displacement with Zinc, Displacement with Magnesium, No reaction with Copper.

Question. Which metals do not corrode easily?
Answer: Gold, platinum, rhodium.

Question. What are alloys?
Answer: Alloy are a homogeneous mixture of two or more metals or a metal and a non-metal. For example, brass is an alloy of copper and zinc.

Question. Which of the following pairs will give displacement reactions?
(a) NaCl solution and copper metal
(b) \( MgCl_2 \) solution and aluminium metal
(c) \( FeSO_4 \) solution and silver metal
(d) \( AgNO_3 \) solution and copper metal.
Answer: (d) \( AgNO_3 \) solution and copper metal.
\( Cu(s) + 2AgNO_3(aq) \rightarrow Cu(NO_3)_2(aq) + 2Ag(s) \) because copper is more reactive than Ag.

Question. Which of the following methods is suitable for preventing an iron frying pan from rusting?
(a) Applying grease
(b) Applying paint
(c) Applying a coating of zinc
(d) All of the options.
Answer: (c) Applying a coating of zinc
Grease and paints are organic matter which can burn on heating. So, we do not apply grease or paint on a frying pan to prevent it from rusting. We can prevent it from rusting by applying coating of zinc. Zinc is more reactive than iron and hence it does not allow iron to rust.

Question. An element reacts with oxygen to give a compound with a high melting point. This compound is also soluble in water. The element is likely to be
(a) calcium.
(b) carbon.
(c) silicon.
(d) iron.
Answer: (a) calcium.
Calcium oxide has high melting point as it is ionic in nature and is soluble in water.

Question. Food cans are coated with tin and not with zinc because
(a) Zinc is costlier than tin.
(b) Zinc has a higher melting point than tin.
(c) Zinc is more reactive than tin.
(d) Zinc is less reactive than tin.
Answer: (c) Zinc is more reactive than tin.
Zinc is more reactive than tin, that is why, tin is used.