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ChemistryClass 10ICSE

When water is added gradually to a white solid X, a hissing sound and a lot of heat is produced forming a product Y. A suspension of Y in water is applied to the walls of a house during white washing. A clear solution of Y is also used for testing carbon dioxide gas in the laboratory. (a) What could be solid X? Write its chemical formula. (b) What could be product Y? Write its chemical formula. (c) What is the common name of the solution of Y which is used for testing carbon dioxide gas? (d) Write chemical equation of the reaction which takes place on adding water to solid X. (e) Which characteristics of chemical reactions are illustrated by this example?

Calcium oxide, Calcium hydroxide, Ca(OH)2 Lime CaO + H2O → Ca(OH)2 Change in

ChemistryClass 10ICSE

When the solution of substance X is added to a solution of potassium iodide, then a yellow solid separates out from the solution. (a) What do you think substance X is likely to be? (b) Name the substance which the yellow solid consists of. (c) Which characteristic of chemical reactions is illustrated by this example? (d) Write a balanced chemical equation for the reaction which takes place. Mention the physical states of all the reactants and products involved in the chemical equation.

Lead Nitrate Lead Iodide Formation of precipitate Pb(NO3)2 (aq) + 2KI (aq) → PbI2 (s) + 2KNO3 (aq)

ChemistryClass 10ICSE

The chemical equations are balanced to satisfy one of the following laws in chemical reactions. This law is known as: (a) Law of conservation of momentum (b) Law of conservation of mass (c) Law of conservation of motion Law of conservation of magnetism

Option (b) is the answer. Equations are balanced when the mass of atoms of different element in reactants side equal to the products side.

ChemistryClass 10ICSE

One of the following is an exothermic reaction. This is: (a) Electrolysis of water (b) Conversion of limestone into quicklime (c) Process of respiration (d) Process of photosynthesis

Option (c) is the answer. Respiration is an exothermic reaction as the heat energy is released which maintains our body temperature.

ChemistryClass 10ICSE

Which of the following is not an endothermic reaction ? (a) CaCO3→ CaO + CO2 (b) 2H2O → 2H2 + O2 (c) 6CO2 + 6H2O → C6H12O6 + 6O2 (d) C6H12O6 + 6O2→ 6CO2 + 6H2O

Option (d) is the answer. This is responsible for the respiration reaction in which glucose burns in oxygen to produce heat energy and thus an exothermic reaction

ChemistryClass 10ICSE

One of the following is an endothermic reaction. This is: (a) Combination of carbon and oxygen to form carbon monoxide (b) Combination of nitrogen and oxygen to form nitrogen monoxide (c) Combination of glucose and oxygen to form carbon dioxide and water Combination of zinc and hydrochloric acid to form zinc chloride and hydrogen

Option (b) is the answer. When nitrogen and oxygen are heated at very high temperature they form nitrogen monoxide and it is a endothermic reaction.

ChemistryClass 10ICSE

The chemical reaction between quicklime and water is characterised by: (a) Evolution of hydrogen gas (b) Formation of slaked lime precipitate (c) Change in temperature of mixture Change in colour of the product

Option (c) is the answer. Reaction of quicklime and water releases higher amount of energy and thus it is an exothermic reaction.

ChemistryClass 10ICSE

The chemical reaction between the two substances is characterised by a change in colour from orange to green. These two substances are most likely to be: (a) Potassium dichromate solution and sulphur dioxide (b) Potassium permanganate solution and sulphur dioxide (c) Potassium permanganate solution and lemon juice Potassium dichromate solution and carbon dioxide

Option (a) is the answer. Reaction between potassium dichromate and sulphur dioxide is characterised by change in colour. The orange colour of acidified potassium dichromate will change into green by passing sulphur dioxide

ChemistryClass 10ICSE

An acid which can decolourise purple coloured potassium permanganate solution is : (a) Sulphuric acid (b) Citric acid (d) Carbonic acid (d) Hydrochloric acid

Option (b) is the answer. Reaction of purple-coloured potassium permanganate with citric acid is characterised by change in colour from purple to colourless

ChemistryClass 10ICSE

You are given the solution of lead nitrate. In order to obtain a yellow precipitate you should mix it with a solution of (a) Potassium chloride (b) Potassium nitride (c) Potassium sulphide Potassium iodide

Option (d) is the answer. When a solution of lead nitrate reacts with potassium iodide it gives yellow precipitate of lead iodide

ChemistryClass 10ICSE

Which one of the following does not involve a chemical reaction? (a) Digestion of food in our body (b) Process of respiration (c) Burning of candle wax when heated Melting of candle wax on heating

Option (d) is the answer. Wax changes its physical state on heating but not the properties so it does not involve any chemical change but involves physical change

ChemistryClass 10ICSE

One of the following does not happen during a chemical reaction This is : (a) Breaking of old chemical bonds and formation of new chemical bonds (b) Formation of new substances with entirely different properties (c) Atoms of one element change into those of another element to form new products A rearrangement of atoms takes place to form new products

Option (c) is the answer. Atoms of one element does not change into another element to form products but the bonds between these atom will break and form products and atoms are rearrange also

ChemistryClass 10ICSE

What do you understand by exothermic and endothermic reactions? (b) Give one example of an exothermic reaction and one of an endothermic reaction. (c) Which of the following are endothermic reactions and which are exothermic reactions? (i) Burning of natural gas (ii) Photosynthesis (iii) Electrolysis of water Solution: (iv) Respiration (v) Decomposition of calcium carbonate

Exothermic reaction is a reaction takes place when energy is released from the system into the surroundings Endothermic reaction is a reaction takes place when energy is absorbed from surroundings in the form of heat The thermal decomposition of Limestone CaCO3(s)&rarr;CaO (s)+CO2(g) This is an example for endothermic reaction Burning of fuel is an example for exothermic reaction C8H18(l)+25O2(g)&rarr;16CO2(g)+18H2O (g)+heat <li

ChemistryClass 10ICSE

State the various characteristics of chemical reactions. (b) State one characteristics each of the chemical reaction which takes place when: (i) Dilute hydrochloric acid is added to sodium carbonate (ii) Lemon juice is added gradually to potassium permanganate solution (iii) Dilute sulphuric acid is added to barium chloride solution (iv) Quicklime is treated with water Wax is burned in the form of a candle

A chemical reaction is a reaction that takes place to form new substance by reacting with It is characterised by Evolution of a gas, Change in colour, Formation of a precipitate, Change in temperature, Change in state. (i) Evolution of Carbon dioxide gas Change in colour from purple to colourless Formation of a white precipitate of Barium sulphate Change in temperature, an exothermic reaction Change in state from solid to liquid and gas

ChemistryClass 10ICSE

What is meant by a chemical reaction? Explain with the help of an example. (b) Give one example each of a chemical reaction characterised by: (i) Evolution of a gas (ii) Change in colour (iii) Formation of a precipitate (iv) Change in temperature Change in state.

A chemical reaction results in new substances by undergoing certain reactions and There will be reactants on the left hand side and products on the right hand side. An example of combustion is methane + oxygen forms carbon dioxide and water. This can be written as a balanced symbol equation: CH4 + 2O2 &rarr;CO2 + 2H2O (i) Evolution of gas Reaction of Zinc and Hydrochloric acid Zn + 2HCl &rarr; ZnCl2 + H2(g)

ChemistryClass 10ICSE

• When potassium nitrate is heated, it decomposes into potassium nitrite and oxygen. Write a balanced equation for this reaction and add the state symbols of the reactants and products.

2KNO3 (s)&rarr; 2KNO2 (s) + O2 (g)

ChemistryClass 10ICSE

Translate the following statement into chemical equation and then balance it: ‘Barium chloride solution reacts with aluminium sulphate solution to form a precipitate of barium sulphate and aluminium chloride solution’.

3BaCl2 (aq) + Al2(SO4)3 (aq) &rarr; 3BaSO4 (s) + 2AlCl3 (aq)

ChemistryClass 10ICSE

Write a balanced chemical equation for the process of photosynthesis giving the physical states of all the substances involved and the conditions of the reaction.

6CO2 (g) + 6H2O (l) &rarr; C6H12O6 (aq.) + 6O2 (g) in the presence of sunlight

ChemistryClass 10ICSE

Ammonia reacts with oxygen to form nitrogen and water. Write a balanced chemical equation for this reaction. Add the state symbols for all the reactants and products.

4NH3 (g) + 3O2 (g) &rarr; 2N2 (g) + 6H2O (l)

ChemistryClass 10ICSE

(a) Substitute formulae for names and balance the following equations: Calcium carbonate reacts with hydrochloric acid to produce calcium chloride, water and carbon dioxide gas. (b) Write balanced chemical equation with state symbols for the following reaction: Sodium hydroxide solution reacts with hydrochloric acid solution to produce sodium chloride solution and water.

(a) CaCO3 + 2HCl &rarr; CaCl2 + H2O + CO2 (b) NaOH (aq) + HCl (aq) &rarr; NaCl (aq) + H2O (l)

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