Science Olympiad Test: Chemical Reactions and Equations- 2 - Class 10 MCQ

Rust is iron oxide. iron is a metal. generally, metallic oxides are basic in nature.
Rust is basic in nature. we know about this because when rust reacts with O₂ and H₂O it releases metallic oxides which are basic in nature.
when we take some amount of rust and put it in a small amount of water and after shaking the liquid when we test the solution with a rd litmus paper, it turns blue. this shows that rust is a basic oxide

It is an example of displacement reaction. Aluminium being more reactive than iron displaces iron and results in the formation of aluminium oxide.

Option 3 is the correct answer.
During the formation of Water, both Hydrogen and Oxygen are in gaseous form and produce Water in liquid form.
The reaction proceeds as follows:
2 H₂ (g) + O₂ (g) → 2 H₂O (l)
The preceding process shows the synthesis of Water from Hydrogen and Oxygen gas.
Two moles of Hydrogen in the gaseous state react with one mole of Oxygen in the gaseous state to form two moles of Water in the liquid state in this reaction.

It forms solution of ferrous sulphate and hydrogen sulphide gas. 
FeS + H₂SO₄ → FeSO_​4 + H₂S.

Sublimation of dry ice and evaporation of water both are endothermic process and these heat (energy) from their surrounding to get sublime or evaporate. Hence, both these processes produce cooling. This is the reason for using dry ice as refrigerant.
Dilution of sulphuric acid and condensation of water vapours evolve heat. Hence, these are exothermic processes.

A strip or sheet of transparent plastic film base is coated with gelatin emulsion containing small light sensitive silver halide crystals on one side.  When the exposed silver halide grains are developed, they are converted to metallic silver which appears as the black part of the film due to blocking of light.
Therefore, the image on an exposed and developed photographic film is due to Ag.

Mole ratio of H₂ to O₂ liberated = 2 : 1.

Copper metal when exposed to air turns green in colour due to corrosion. Thus, when copper vessels are exposed to air in rainy season for sometime, the metal reacts with gases and moisture present in air to form a mixture of copper carbonate and copper hydroxide [(CuCO₃).Cu(OH)₂]. This gives a green colour to the vessels

Oxidised: PbS: The oxidation number of S increases from -2 to +6. Thus, S itself is oxidised and acts as reducing agent.
Reduced: H₂​O₂​: The oxidation number of O decreases from -1 to -2. Thus, O itself is reduced and acts as oxidising agent.

• The Law of conservation of mass states that mass can neither be created nor destroyed but can be transformed from one form to another.
• A balanced chemical equation is in accordance with the law of conservation of mass i.e the atoms of the reactants are just rearranged to form products but the total amount of mass in chemical reaction remains constant.
• Avogadro's Law states that at the constant temperature and pressure, the volumes of gas is directly proportional to the number of molecules.
• Law of multiple proportion states that when two elements combine to form two or more compounds, then the ratio of the mass of one element that combines with the fixed mass of the other element will always be simple whole numbers.
• Gay-Lussac's Law of gaseous volumes states that at constant volume, the pressure of the given mass of a gas is directly proportional to the temperature in Kelvin.

• Hydrogen gas is not evolved when there is a reaction between metal and Nitric acid (HNO₃)occurs as Nitric acid is a strong oxidizing agent.
• The Hydrogen gas produced during the reaction with metal gets oxidized to H2O, hence no hydrogen gas is produced.
• Instead, it evolves nitric oxides such as NO₂​,NO etc.
• Example: When a Silver metal reacts with Nitric acid (HNO₃)to give N₂O and H₂O.

The mixing or dissolution of Sodium chloride in water is an endothermic reaction, i.e. when it takes place it increases the temperature of the solution by absorption of heat resulting in increase in temperature of the reaction mixture which increases the solubility of sodium chloride.

The evaporation of water is a physical change. When water evaporates, it changes from the liquid state to the gas state, but it is still water; it has not changed into any other substance. All changes of state are physical changes.

The reactions in which two compounds react by an exchange of ions to form two new compounds are called double displacement reactions. In double replacement reactions, the positive ions exchange negative ion partners. A double replacement reaction is represented by the general equation.
AB + CD → AD + CB
In a double displacement reaction, atoms from two different compounds switch places. The reactants are two compounds and the products are two different compounds.
Na₂SO₄ + BaCl₂ → BaSO₄ + 2NaCl

Exothermic reactions are chemical reactions that release energy as heat or light.

• A large amount of heat is released when quick lime reacts with water, along with the formation of calcium hydroxide.
• Similarly, the process of dissolving an acid or base in water is a highly exothermic reaction. Water should never be added to acid, but the acid can be added to water for dilution.
• Evaporation of water and sublimation of camphor are endothermic reactions.