NCERT
- Under what soil condition do you think a farmer would treat the soil of his fields with quick lime If the soil is acidic and improper for cultivation, then to increase the basicity of soil, the farmer would treat the soil with quick lime o... 1
- Do basic solutions also have H+ (aq) ions? If yes, then why are these basic? Yes, basic solution also has H⁺ ions. However, their concentration is less as compared to the concentration of OH⁻ ions that makes the solut... 1
- What effect does the concentration of H+ (aq) ions have on the nature of the solution? If the concentration of H⁺ (aq) ions is increased (>10-7) then the solution become acidic and if the concentration of H⁺ (aq) ions is decrea... 1
- You have two solutions, A and B. The pH of solution A is 6 and pH of solution B is 8. A pH value of less than 7 indicates an acidic solution, while greater than 7 indicates a basic solution. Therefore, the solution with pH = 6... 1
- How is the concentration of hydroxide ions (OH−) affected when excess base is dissolved The concentration of hydroxide ions (OH⁻) would increase when excess base is dissolved in a solution of sodium hydroxide. 1
- How is the concentration of hydronium ions (H3O+) affected when a solution of an acid is diluted? When an acid is diluted, the concentration of hydronium ions (H₃O⁺) per unit volume decreases. This means that the strength of the acid decr... 1
- While diluting an acid, why is it recommended that the acid should be added to water Since the process of dissolving an acid in water is exothermic, it is always recommended that acid should be added to water. If it is done t... 1
- Why does dry HCl gas not change the colour of the dry litmus paper? Dry HCl gas not change the colour of the dry litmus paper because it has no Hydrogen ions (H⁺) in it. 1
- Why does an aqueous solution of an acid conduct electricity? The presence of hydrogen (H⁺) or hydronium (H₃O⁺) ions in the aqueous solution of an acid are responsible for conducting electricity. 1
- Why do HCl, HNO3, etc., show acidic characters in aqueous solutions while solutions of compounds When HCl or HNO₃ are mixed with water then they dissolve in water to form H⁺ or H₃O⁺ ions which shows their acidic character. For example ju... 1
- Metal compound A reacts with dilute hydrochloric acid to produce effervescence. CaCO₃ (s) + 2HCl (aq) → CaCl₂ (aq) + CO₂ (g) + H₂O (l) Calcium Carbonate + Hydrochloric acid → Calcium Chloride + Carbon dioxide + Water 1
- Which gas is usually liberated when an acid reacts with a metal? Hydrogen gas is usually liberated when an acid reacts with a metal For example: When zinc granules react with dilute sulphuric acid, then hy... 1
- Why should curd and sour substances not be kept in brass and copper vessels? Curd and other sour substances contain acids. Therefore, when they are kept in brass and copper vessels, the metal reacts with the acid to l... 2
- You have been provided with three test tubes. One of them contains distilled water Answer: Use red litmus to find the base first, then use the blue litmus obtained from it to find the acid; the remaining tube is distilled w... 1
- Explain the following terms with one example each. (a) Corrosion (b) Rancidity Corrosion is defined as a process where materials, usually metals, deteriorate as a result of a chemical reaction with air, moisture, chemic... 1
- Oil and fat containing food items are flushed with nitrogen. Why? Oil and fat containing food items flushed with nitrogen because nitrogen acts as an antioxidant and it prevents them from being oxidised 2
- Why do we apply paint on iron articles? Iron articles are painted because it prevents them from rusting. When painted, the contact of iron articles from moisture and air is cut off... 1
- A shiny brown-coloured element ‘X’ on heating in air becomes black in colour. Element 'X' is copper and the black coloured compound is copper (11) oxide Equation: 2Cu_((s)) + O_(2(g) )→ 2CuO_((s)) 1
- Explain the following in terms of gain or loss of oxygen with two examples each. Oxidation: Addition of oxygen or electronegative element to a atom, molecule, or ion or removal of hydrogen or electropositive element from... 1
- What do you mean by a precipitation reaction? Explain by giving examples. A reaction in which an insoluble solid (called precipitate) is formed is called a precipitation reaction.For Example: Na₂CO₃ (aq) + CaCl₂ (a... 1
- In the refining of silver, the recovery of silver from silver nitrate solution involved displacement 2AgNO₃ (aq) + Cu (s) → Cu(NO₃)₂ (aq) + 2Ag (s) Silver Nitrate + Copper → Copper Nitrate + Silver 1
- What is the difference between displacement and double displacement reactions? In a displacement reaction, a more reactive element replaces a less reactive element from a compound. For Example: CuSo₄ (aq) + Zn (s) → ZnS... 1
- Write one equation each for decomposition reactions where energy is supplied Thermal decomposition : read the image for answer https://lh3.googleusercontent.com/-CpMGoV1AuvA/Ya3V5xIPrnI/AAAAAAAAC3I/6WMqQz11TQc2TSOK9X6... 2
- Why are decomposition reactions called the opposite of combination reactions? Decomposition reactions are those in which a compound breaks down to form two or more substances. These reactions require a source of energy... 1