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Metals and Non-metals - 3.43.4 3.43.4 OCCURRENCE OF METOCCURRENCE OF METOCCURRENCE OF METOCCURRENCE OF METOCCURRENCE OF MET ALS ALSALSALSALS

Grade 10CBSE

Review the key concepts, formulae, and examples before starting your quiz.

🔑Concepts

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Minerals and Ores: Naturally occurring elements or compounds in the earth's crust are called minerals. Minerals that contain a very high percentage of a particular metal and from which the metal can be profitably extracted are called ores.

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Gangue: Ores mined from the earth are usually contaminated with large amounts of impurities such as soil and sand, which are called gangue.

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Reactivity Series and Extraction: Metals are extracted based on their position in the activity series. Metals of low reactivity (like AuAu, AgAg) are found in a free state. Metals of medium reactivity (ZnZn, FeFe, PbPb) occur as oxides, sulphides, or carbonates. Metals of high reactivity (KK, NaNa, CaCa, MgMg, AlAl) are never found as free elements and are extracted by electrolysis.

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Roasting: The process of heating sulphide ores strongly in the presence of excess air to convert them into oxides. For example: 2ZnS(s)+3O2(g)→Heat2ZnO(s)+2SO2(g)2ZnS(s) + 3O_2(g) \xrightarrow{\text{Heat}} 2ZnO(s) + 2SO_2(g).

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Calcination: The process of heating carbonate ores strongly in limited air to convert them into oxides. For example: ZnCO3(s)→HeatZnO(s)+CO2(g)ZnCO_3(s) \xrightarrow{\text{Heat}} ZnO(s) + CO_2(g).

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Reduction: Metal oxides are reduced to the corresponding metals using reducing agents like carbon (coke) or highly reactive metals (like NaNa, CaCa, AlAl). Example: ZnO(s)+C(s)→Zn(s)+CO(g)ZnO(s) + C(s) \rightarrow Zn(s) + CO(g).

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Thermite Process: The reaction of iron(III) oxide with aluminium is highly exothermic; the iron produced is in a molten state. This is used to join railway tracks or cracked machine parts: Fe2O3(s)+2Al(s)→2Fe(l)+Al2O3(s)+HeatFe_2O_3(s) + 2Al(s) \rightarrow 2Fe(l) + Al_2O_3(s) + \text{Heat}.

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Electrolytic Refining: For refining impure metals like copper. The anode is made of impure metal, the cathode is a thin strip of pure metal, and the electrolyte is a solution of the metal salt. Pure metal deposits on the cathode.

📐Formulae

2ZnS+3O2→Δ2ZnO+2SO22ZnS + 3O_2 \xrightarrow{\Delta} 2ZnO + 2SO_2

ZnCO3→ΔZnO+CO2ZnCO_3 \xrightarrow{\Delta} ZnO + CO_2

ZnO+C→Zn+COZnO + C \rightarrow Zn + CO

Fe2O3+2Al→2Fe+Al2O3+HeatFe_2O_3 + 2Al \rightarrow 2Fe + Al_2O_3 + \text{Heat}

MnO2+4Al→3Mn+2Al2O3+HeatMnO_2 + 4Al \rightarrow 3Mn + 2Al_2O_3 + \text{Heat}

At Cathode (Electrolysis of NaCl):Na++e−→Na\text{At Cathode (Electrolysis of NaCl)}: Na^+ + e^- \rightarrow Na

At Anode (Electrolysis of NaCl):2Cl−→Cl2+2e−\text{At Anode (Electrolysis of NaCl)}: 2Cl^- \rightarrow Cl_2 + 2e^-

💡Examples

Problem 1:

A carbonate ore of metal MM on heating gives a gas that turns lime water milky and leaves a metal oxide. Name the process and write the chemical equation if the metal is Zinc (ZnZn).

Solution:

The process is Calcination. Equation: ZnCO3(s)→ΔZnO(s)+CO2(g)ZnCO_3(s) \xrightarrow{\Delta} ZnO(s) + CO_2(g).

Explanation:

Carbonate ores are heated in limited air (calcination) to release CO2CO_2 gas, which turns lime water milky.

Problem 2:

Explain why sodium metal cannot be obtained by reducing sodium oxide with carbon.

Solution:

Sodium is high in the reactivity series. It has a higher affinity for oxygen than carbon does. Therefore, carbon cannot remove oxygen from sodium oxide to reduce it to sodium metal.

Explanation:

Metals like NaNa, MgMg, and AlAl are extracted by the electrolytic reduction of their molten chlorides or oxides because they are more reactive than carbon.

Problem 3:

During the electrolytic refining of copper, name the substances used as the anode and the cathode.

Solution:

Anode: Impure Copper block; Cathode: Thin strip of pure Copper.

Explanation:

In electrolytic refining, the metal to be purified is made the anode, and a pure strip of the same metal is made the cathode. Upon passing current, pure metal from the anode dissolves into the electrolyte and deposits onto the cathode.