| # | Statement (Answer in bold) |
|---|---|
| 1 | If the electronegativity difference between two bonded atoms in a molecule is greater than 1.7, the nature of bonding is ionic. |
| 2 | 6th and 7th are the longest periods in the periodic table; each has 32 elements. |
| 3 | Atomic number forms the basis of modern periodic table. |
| 4 | If the distance between two Cl atoms in Cl2 molecule is 1.98 Å, then the radius of Cl atom is 0.99 Å. |
| 5 | Among the given species A-, A+ and A, the smallest one in size is A+. |
| 6 | The scientist who propounded the modern periodic law is Henry Moseley. |
| 7 | Across the period, ionic radii decreases. |
| 8 | Lanthanides and actinides are called inner transition elements. |
| 9 | The chief ore of aluminium is bauxite. |
| 10 | The chemical name of rust is hydrated ferric oxide. |
| Column A | Column B |
|---|---|
| Dental filling : silver | silver amalgam (dental amalgam) |
| # | Statement | Answer | Correction (if False) |
|---|---|---|---|
| 1 | Moseley's periodic table is based on atomic mass. | False | Moseley's periodic table is based on atomic number. |
| 2 | Ionic radius increases across the period from left to right. | False | Ionic radius decreases across the period from left to right. |
| 3 | All ores are minerals; but all minerals cannot be called ores. | True | |
| 4 | Al wires are used as electric cables due to their silvery white colour. | False | Al wires are used in electric cables because they are good conductors. |
| 5 | An alloy is a heterogenous mixture of metals. | False | An alloy is a homogeneous mixture of metals. |
Answer: iv. Assertion is false, but Reason is true. HF has a polar covalent bond, not an ionic bond.
Answer: i. Both Assertion and Reason are true, and Reason correctly explains the Assertion. Magnesium acts as a sacrificial metal and protects steel from rusting.
Answer: ii. Both Assertion and Reason are true, but Reason does not explain the Assertion. The green layer on copper is basic copper carbonate formed by reaction with air, moisture and carbon dioxide.
At a temperature below 1370 K, copper forms black copper(II) oxide:
2Cu + O2 -> 2CuO
So, B is copper(II) oxide (CuO).
At a temperature above 1370 K, copper forms red copper(I) oxide:
4Cu + O2 -> 2Cu2O
So, C is copper(I) oxide (Cu2O).
4Al + 3O2 -> 2Al2O3
So, B is aluminium oxide (Al2O3). Aluminium alloys are used in making aircraft because they are light and strong.
4Fe + 3O2 + xH2O -> 2Fe2O3.xH2O (rust)
Rusting, the common term for the corrosion of iron and its alloys, is an electrochemical process that requires specific environmental conditions to occur. The two primary conditions necessary for the rusting of iron are the presence of oxygen and the presence of water or moisture. Oxygen acts as an oxidizing agent, while water serves as an electrolyte, facilitating the movement of ions and completing the electrochemical circuit. In the absence of either oxygen or moisture, iron will not rust. For example, iron kept in dry air or in vacuum-sealed containers does not rust, nor does iron submerged in oil or other non-aqueous liquids.
a) During the purification of bauxite ore, caustic soda solution (sodium hydroxide, NaOH) is added to dissolve the alumina (Al₂O₃) present in the ore. Alumina reacts with the hot, concentrated caustic soda solution to form soluble sodium meta-aluminate (Na[Al(OH)₄] or NaAlO₂), while the impurities like iron oxides, silica, and titanium dioxide, which are insoluble in alkali, remain undissolved. This selective dissolution allows for the separation of alumina from its ore. b) Along with cryolite (Na₃AlF₆) and alumina (Al₂O₃), another substance, fluorspar (CaF₂), is added to the electrolyte mixture in the electrolytic refining of aluminum. The primary reason for adding fluorspar is to lower the fusion temperature of the mixture. Pure alumina has a very high melting point (over 2000°C), making electrolysis impractical and energy-intensive. The addition of cryolite and fluorspar significantly lowers the melting point of the electrolyte to around 900-1000°C, reducing energy consumption and increasing the fluidity of the molten bath, which improves the efficiency of the electrolysis process.
2Cu + O2 + CO2 + H2O -> CuCO3.Cu(OH)2
So, B is basic copper carbonate.
With concentrated sulphuric acid, copper forms copper sulphate, sulphur dioxide and water:
Cu + 2H2SO4 -> CuSO4 + SO2 + 2H2O
So, C is copper sulphate (CuSO4) and D is sulphur dioxide (SO2).
Smelting is a pyrometallurgical process used to extract a metal from its ore by heating it strongly in the presence of a reducing agent, typically in a furnace. The primary objective of smelting is to reduce the metallic oxide ore to its molten metallic state. During this process, a flux, which is a chemical agent like limestone or silica, is often added. The flux reacts with the unwanted impurities in the ore (such as silica, alumina, or basic oxides) to form a molten slag. This slag has a lower melting point than the metal and is immiscible with it, allowing it to be easily separated from the molten metal by decantation or tapping. Smelting is a crucial step in the extraction of many important metals, including iron, copper, lead, and tin.
In red hot condition, aluminium reacts with steam to form aluminium oxide:
2Al + 3H2O -> Al2O3 + 3H2
So, B is aluminium oxide (Al2O3).
With strong alkali, aluminium forms sodium meta aluminate:
2Al + 2NaOH + 2H2O -> 2NaAlO2 + 3H2
So, C is sodium meta aluminate (NaAlO2).
Nitric acid renders aluminium passive. This phenomenon, known as passivation, occurs because nitric acid oxidizes the surface of the aluminium metal. A thin, adherent, and protective layer of aluminium oxide (Al2O3) is formed on the aluminium's surface. This oxide film acts as a barrier, preventing further reaction between the underlying aluminium metal and the nitric acid. Therefore, the aluminium is rendered passive and does not react with the acid.
a) The bond between H and F in the HF molecule is a polar covalent bond. b) This identification is based on the significant difference in electronegativity between hydrogen and fluorine. Fluorine is highly electronegative, while hydrogen is less electronegative. This unequal sharing of electrons creates a partial positive charge on the hydrogen atom and a partial negative charge on the fluorine atom, resulting in a polar bond. c) Electronegativity generally increases from left to right across a period in the periodic table due to an increasing nuclear charge and a decrease in atomic radius. Conversely, electronegativity decreases as one moves down a group because the atomic radius increases and the outermost electrons are farther from the nucleus, experiencing less attraction.
Study Smarter, Score Higher.
Revise this Samacheer Class 10 Science topic, then continue with the Revision Challenge.