Explain why most of the metal articles become dull when kept exposed to air ?

(i) Solution of a substance 'X' is used for testing carbon dioxide. Write the equation of the reaction of 'X' with carbon dioxide.
(ii) How is 'X' obtained? Write chemical equation.

Identify the type of each of the following reactions. Also write balanced chemical equation for each.
(i) The reaction mixture becomes warm.
(ii) An insoluble substance is formed.

Write the balanced chemical equation for the following and identify the type of reaction in each case.
(a) Potassium bromide(aq) + Barium Iodide(aq) \(\rightarrow\) Potassium iodide(aq) + Barium bromide(s)
(b) Zinc carbonate(s) → Zinc oxide(s) + Carbon dioxide(g)
(c) Hydrogen(g) + Chlorine(g) → Hydrogen chloride(g)
(d) Magnesium(s) + Hydrochloric acid(aq) → Magnesium chloride(aq) + Hydrogen(g)

What is a balanced chemical equation? Why should chemical equations be balanced?

Write the balanced equation for the following chemical reactions.
(i) Hydrogen + Chlorine \(\rightarrow\) Hydrogen chloride
(ii) Barium chloride + Aluminium sulphate \(\rightarrow\) Barium sulphate + Aluminium chloride
(iii) Sodium + Water \(\rightarrow\) Sodium hydroxide + Hydrogen

When you heat few crystals of sugar in dry test tube, what do you obtain and why?

Products formed when A and B react together are zinc chloride and hydrogen gas. Find reactants A and B.

What is meant by a chemical reaction?

Write one equation each for decomposition reactions where energy is supplied in the form of heat, light or electricity.

Write the balanced chemical equations for the following reactions.
(a) Calcium hydroxide + Carbon dioxide \(\rightarrow\) Calcium carbonate + Water
(b) Zinc + silver nitrate \(\rightarrow\) Zinc nitrate + Silver
(c) Aluminium + Copper chloride \(\rightarrow\) Aluminium chloride + Copper
(d) Barium chloride + Potassium Sulphate \(\rightarrow\) Barium sulphate + Potassium chloride

A solution of a substance 'X' is used for white washing.
(i) Name the substance 'X' and write its formula.
(ii) Write the reaction of the substance 'X' named in (i) above with water.

Assertion: A lead nitrate on thermal decomposition gives lead oxide, brown coloured nitrogen dioxide and oxygen gas.
Reason: Lead nitrate reacts with potassium iodide to form yellow ppt of lead iodide and the reaction is double displacement as well as precipitation reaction.
Codes
(a) Both A and R are true, and R is correct explanation of the assertion.
(b) Both A and R are true, but R is not the correct explanation of the assertion.
(c) A is true, but R is false.
(d) A is false, but R is true.

Assertion: Chips manufacturers usually flush bags of chips with gas such as nitrogen to prevent the chips from getting oxidised.
Reason: This increase the taste of the chips and helps in their digestion.
Codes
(a) Both A and R are true, and R is correct explanation of the assertion.
(b) Both A and R are true, but R is not the correct explanation of the assertion.
(c) A is true, but R is false.
(d) A is false, but R is true.

Assertion: In a balanced chemical equation, total mass of the reactants is equal to the total mass of the products.
Reason: Mass can neither be created nor destroyed during a chemical change.
Codes
(a) Both A and R are true, and R is correct explanation of the assertion.
(b) Both A and R are true, but R is not the correct explanation of the assertion.
(c) A is true, but R is false.
(d) A is false, but R is true.

Assertion: Food materials are often packed in air tight container.
Reason: Oxidation, resulting in rancidity, is prevented
Codes
(a) Both A and R are true, and R is correct explanation of the assertion.
(b) Both A and R are true, but R is not the correct explanation of the assertion.
(c) A is true, but R is false.
(d) A is false, but R is true.

Assertion: CO + 2H₂ \(\xrightarrow[{\triangle }]{340 \ atm}\) CH₃OH(l)
Reason: It is a combination reaction because CO combines with H₂ to form CH₃OH i.e., two substances combine to form a single compound.
Codes
(a) If both assertion and reason are true and the reason is correct explanation of assertion.
(b) If both assertion and reason are true but reason is not a correct explanation of assertion.
(c) If assertion is true and reason is false.
(d) If both assertion and reason are false.

Marble's popularity began in ancient Rome and Greece, where white and off-white marble were used to construct a variety of structures, from hand-held sculptures to massive pillars and buildings.


(i) A student added 10 g of calcium carbonate in a rigid container, secured it tightly and started to heat it. After some time, an increase in pressure was observed, the pressure reading was then noted at intervals of 5 min and plotted against time, in a graph as shown below. During which time interval did maximum decomposition took place?

(ii) Calcium oxide can be reduced to calcium, by heating with sodium metal. Which compound would act as an oxidising agent in the given process and why?
(iii) Gas obtained in (i) is a reactant for a very important biochemical process which occurs in the presence of sunlight. ldentify the name of the process.
(iii) Marble statues are corroded or stained when they repeatedly come in contact with polluted rain water. What could be the main reason? Write the chemical decomposition of calcium carbonate.

Chemical reaction, a process in which one or more substances, the reactants, are converted to one or more different substances, the products. Substances are either chemical elements or compounds. A chemical reaction rearranges the constituent atoms of the reactants to create different substances as products. Study this table related to the different types of reactions / processes and answer the questions that follow.

(i) The reaction in which two or more substances combine to form a single substance under suitable conditions is
(a) combination reaction       (b) combustion
(c) decomposition reaction  (d) photosynthesis
(ii) Which of the following is essential for photosynthesis?
(a) Sunlight (b) Chlorophyll (c) Glucose (d) Both 'a' and 'b’
Photosynthesis is the process by which green plants and some other organisms use sunlight to synthesis nutrients from carbon dioxide and water.
(iii) When a chemical compound decomposes on absorbing light and energy, then the reaction which takes place is known as
(a) photosynthesis     (b) photodecomposition
(c) combination          (d) thermal decomposition.
A photodecomposition is a chemical reaction in which an inorganic chemical (or an organic chemical) is broken down by photons and is the interaction of one or more photons with one target molecule.
(iv) Which of the following reactions is an example of combustion reaction ?
\((a) \mathrm{C}_{(s)}+\mathrm{O}_{2(g)} \longrightarrow \mathrm{CO}_{2(g)}\\ (b) \mathrm{Zn}_{(s)}+\mathrm{H}_{2} \mathrm{SO}_{4(a q)} \longrightarrow \mathrm{ZnSO}_{4(a q)}+\mathrm{H}_{2(g)}\\ (c) \mathrm{Zn}_{(s)}+2 \mathrm{HCl}_{(a q)} \longrightarrow \mathrm{ZnCl}_{2(a q)}+\mathrm{H}_{2(g)}\\ (d) 3 \mathrm{Mg}_{(s)}+\mathrm{N}_{2(g)} \longrightarrow \mathrm{Mg}_{3} \mathrm{~N}_{2(s)}\)
A combustion reaction is a reaction in which a substance reacts with oxygen gas, releasing energy in the form of light and heat.
(v) Which of the following is an example of combination reaction?
\((a) \mathrm{H}_{2(g)}+\mathrm{Cl}_{2(g)} \stackrel{\text { light }}{\longrightarrow} 2 \mathrm{HCl}_{(g)}\\ (b) \mathrm{Fe}_{(s)}+S_{(s)} \longrightarrow \mathrm{FeS}_{(g)}\\ (c) 2 \mathrm{H}_{2(g)}+\mathrm{O}_{2(g)} \longrightarrow 2 \mathrm{H}_{2} \mathrm{O}_{(l)}\\ (d) All \ of \ them\)
A combination reaction (also known as a synthesis reaction) is a reaction where two or more elements or compounds (reactants) combine to form a single compound (product).