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Give the characteristic tests for the following gases (a) CO2 (b) SO2 (c) O2 (d) H2

Answer: Limewater is basically a solution of calcium hydroxide. So if we bubble carbon dioxide through the solution it reacts with calcium... View Article

A silver article generally turns black when kept in the open for a few days. The article when rubbed with toothpaste again starts shining. (a) Why do silver articles turn black when kept in the open for a few days? Name the phenomenon involved. (b) Name the black substance formed and give its chemical formula.

Answer: (a) There are traces of hydrogen sulphide (H2S) gas in the air. Silver sulphide is formed as H2S slowly reacts with the silver in the... View Article

Zinc liberates hydrogen gas when reacted with dilute hydrochloric acid, whereas copper does not. Explain why?

Answer: Zinc is more reactive than copper as Zinc is placed above Hydrogen and Copper is placed below hydrogen in the activity series of metals.... View Article

A magnesium ribbon is burnt in oxygen to give a white compound X accompanied by emission of light. If the burning ribbon is now placed in an atmosphere of nitrogen, it continues to burn and forms a compound Y. (a) Write the chemical formulae of X and Y. (b) Write a balanced chemical equation, when X is dissolved in water.

Answer: The Compound ‘X’ is magnesium oxide (MgO). The compound ‘Y’ is magnesium nitride (Mg3N2) 2Mg + O2 → 2MgO 3Mg... View Article

Balance the following chemical equations and identify the type of chemical reaction. (a) Mg(s) + Cl2 (g) → MgCl2 (s) (b) HgO(s) → Heat Hg(l) + O2 (g) (c) Na(s) + S(s) → Fuse Na2S(s) (d) TiCl4 (l) + Mg(s) → Ti(s) + MgCl2 (s) (e) CaO(s) + SiO2 (s) → CaSiO3 (s) (f) H2O2 (l) → U V H2O(l) + O2 (g)

Answer: A chemical reaction is in which the bonds are broken within reactant molecules, and new bonds are formed within product molecules in... View Article

Write a balanced chemical equation for the given reaction and also classify them : Hydrogen sulphide gas reacts with oxygen gas to form solid sulphur and liquid water.

Answer: Balancing chemical equation refers to balancing the stoichiometric coefficients on the reactants and products side. This must be done as... View Article

Write a balanced chemical equation for the given reaction and also classify them : Iron (III) oxide on heating with carbon monoxide gas reacts to form solid iron and liberates carbon dioxide gas.

Answer: Balancing chemical equation refers to balancing the stoichiometric coefficients on the reactants and products side. This must be done as... View Article

Write a balanced chemical equation for the given reaction and also classify them : A piece of sodium metal is added to absolute ethanol to form sodium ethoxide and hydrogen gas.

Answer: Balancing chemical equation refers to balancing the stoichiometric coefficients on the reactants and products side. This must be done as... View Article

Write a balanced chemical equation for the given reaction and also classify them: Lead acetate solution is treated with dilute hydrochloric acid to form lead chloride and acetic acid solution.

Answer: Balancing chemical equation refers to balancing the stoichiometric coefficients on the reactants and products side. This must be done as... View Article

A substance X, which is an oxide of a group 2 element, is used intensively in the cement industry. This element is present in bones also. On treatment with water, it forms a solution which turns red litmus blue. Identify X and also write the chemical reactions involved.

Answer: Compound X is CaO(Calcium oxide). CaO is extensively used in the cement industry. On treatment with water, CaO produces Ca(OH)2 which is... View Article

During the reaction of some metals with dilute hydrochloric acid, the following observations were made. (a) Silver metal does not show any change (b) The temperature of the reaction mixture rises when aluminium (Al) is added. (c) The reaction of sodium metal is found to be highly explosive Some bubbles of gas are seen when lead (Pb) is reacted with the acid. Explain these observations giving suitable reasons.

Answer: (a) Silver (Ag) is placed below hydrogen in the activity series. It cannot replace hydrogen from dilute HCl and no chemical reaction is... View Article

Which among the following are physical or chemical changes? (a) Evaporation of petrol (b) Burning of Liquefied Petroleum Gas (LPG) (c) Heating of an iron rod to red hot. (d) Curdling of milk (e) Sublimation of solid ammonium chloride

Answer: A substance is said to undergo a physical change when only the physical properties such as the shape, size, colour, state or appearance... View Article

Grapes hanging on the plant do not ferment but after being plucked from the plant can be fermented. Under what conditions do these grapes ferment? Is it a chemical or a physical change?

Answer: Physical change - A substance is said to undergo a physical change when only the physical properties such as the shape, size, colour,... View Article

Ferrous sulphate decomposes with the evolution of a gas having a characteristic odour of burning sulphur. Write the chemical reaction involved and identify the type of reaction.

Answer: The above reaction is an example of a decomposition reaction. In a decomposition reaction, a single reactant decomposes to form a... View Article

A solution of potassium chloride when mixed with silver nitrate solution, an insoluble white substance is formed. Write the chemical reaction involved and also mention the type of chemical reaction?

Answer: KCl(aq) + AgNO3(aq) → AgCl(s) + KNO3(aq) This is a double displacement and precipitation reaction. Those reactions in which two... View Article

Write the balanced chemical equations for the given reactions: Copper sulphate on treatment with potassium iodide precipitates cuprous iodide (Cu₂I₂), liberates iodine gas and also forms potassium sulphate.

Answer: Balancing chemical equation refers to balancing the stoichiometric coefficients on the reactants and products side. This must be done as... View Article

Write the balanced chemical equations for the given reactions: Sodium hydrogencarbonate on reaction with hydrochloric acid gives sodium chloride, water and liberates carbon dioxide.

Answer: Balancing chemical equation refers to balancing the stoichiometric coefficients on the reactants and products side. This must be done as... View Article

Write the balanced chemical equations for the given reactions: Sodium carbonate on reaction with hydrochloric acid in equal molar concentrations gives sodium chloride and sodium hydrogencarbonate.

Answer: Balancing chemical equation refers to balancing the stoichiometric coefficients on the reactants and products side. This must be done as... View Article

Identify the oxidising agent (oxidant) in the following reactions (a) Pb3O4 + 8HCl → 3PbCl2 + Cl2 + 4H2O (b) 2Mg + O2 → 2MgO (c) CuSO4 + Zn → Cu + ZnSO4 (d) V2O5 + 5Ca → 2V + 5CaO (e) 3Fe + 4H2O → Fe3O4 + 4H2 (f) CuO + H2 → Cu + H2O

Answer: An oxidizing agent (often referred to as an oxidizer or an oxidant) is a chemical species that tends to oxidize other substances, i.e.... View Article

Identify the reducing agent in the following reactions (a) 4NH3 + 5O2 → 4NO + 6H2O (b) H2O + F2 → HF + HOF (c) Fe2O3 + 3CO → 2Fe + 3CO2 (d) 2H2 + O2 → 2H2O

Answer: A substance that loses electrons to other substances in a redox reaction and gets oxidized to the higher valency state is called a... View Article

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