Q: Question 4Give a balanced equation for addition of iron to copper [II] sulphate solution. State the change in color seen.

CuSO4Blue+Fe⟶FeSO4Light green+CuBrownish red\underset{\text{Blue}}{\text{CuSO}_4} + \text{Fe} \longrightarrow \underset{\text{Light green}}{\text{FeSO}_4} + \underset{\text{Brownish red}}{\text{Cu}}BlueCuSO4+Fe⟶Light greenFeSO4+Brownish redCuColour changes from blue to light green.

Q: Question 9Give one example in each case where supplying energy [given below] is necessary for a chemical reaction.(a) Heat energy(b) Light energy(c) Electrical energy(d) Pressure(e) Catalyst

(a) ZnCO3 →Δ\xrightarrow{\Delta}Δ ZnO + CO2 [g](b) H2 + Cl2 →sunlight\xrightarrow{\text{sunlight}}sunlight 2HCl(c) 2H2O→currentelectric2H2+O22\text{H}_2\text{O} \xrightarrow[\text{current}]{\text{electric}} 2\text{H}_2 + \text{O}_22H2Oelectriccurrent2H2+O2(d) N2+3H2⇌450°C Fe/200 atmos press2NH3\text{N}_2 + 3\text{H}_2 \xrightleftharpoons [450\text{\degree C }]{\text{Fe/200 atmos press}} 2\text{NH}_3N2+3H2Fe/200 atmos press450°C 2NH3 + Δ(e) 4NH3 + 5O2 →Pt-800 °C\xrightarrow{\text{Pt-800 \degree C}}Pt-800 °C 4NO + 6H2O + Δ

Question 1

Question 1(a) Define a chemical reaction.(b) What is a chemical equation?(c) Why do we need to balance chemical equations?

Accepted Answer

(a) Any chemical change in matter which involves its transformation into one or more new substances is called a chemical reaction.(b) A chemical reaction can be represented with the help of symbols or the formulae of the elements and the compounds taking part in the reaction and the product formed, in the form of a chemical equation.(c) A chemical equation needs to be balanced so as to make the number of atoms of the reactants equal to the number of atoms of the products because a chemical reaction is just a rearrangement of atoms. The atoms themselves are neither created nor destroyed during the course of a chemical reaction.

Question 2

Question 2State four conditions necessary for chemical reactions to take place.

Accepted Answer

The four conditions necessary for chemical reactions to take place are:Close contact: For a chemical reaction to take place the reactants must come into close contact i.e. they should be mixed.Solution form: Some substances react with each other only when they are mixed in solution form.Heat: Some reactants need to be heated to undergo a chemical change.Light: Some reactions take place in the presence of light.

Question 3

Question 3Differentiate between:(a) Reactants and products(b) Chemical reaction and chemical equation(c) A balanced and a skeletal chemical equation

Accepted Answer

(a) Difference between reactants and products :ReactantsProductsThe substances that undergo chemical change are called reactants.The new substances formed as a result of reaction are called products.Reactants are written on the left hand side of the equation.Products are written on the right hand side of the equation.In equation C + O2 ⟶ CO2, C and O2 are reactants.In equation C + O2 ⟶ CO2, CO2 is product.(b) Difference between chemical reaction and chemical equation :Chemical reactionChemical equationAny chemical change in matter which involves its transformation into one or more new substances is called a chemical reaction.A chemical reaction can be represented with the help of symbols or the formulae of the elements and the compounds taking part in the reaction in the form of a chemical equation.Example of chemical reaction is burning of candle.Example — 2H2 + O2 ⟶ 2H2O(c) Difference between a balanced and a skeletal chemical equation :Balanced chemical equationSkeletal chemical equationIn balanced chemical equation the total number of atoms on the reactant side as well as the product side are equal.In skeletal chemical equation the total number of atoms on the reactant side and product side are not equal.Example:Zn + H2SO4 ⟶ ZnSO4 + H2Example:H2 + O2 ⟶ H2O

Question 4

Question 5Write your observations for the following chemical reactions and name the products formed:(a) When sugar is heated.(b) When manganese dioxide is added to potassium chlorate and heated.(c) When dilute acetic acid is poured on baking soda.(d) When an aqueous solution of sodium chloride is mixed with an aqueous solution of silver nitrate.(e) When ammonium chloride is heated with sodium hydroxide.(f) When water is added to quick lime.

Accepted Answer

(a) When sugar is heated it first melts and then gets charred into a black residue. The products formed are charcoal and water vapour.(b) When manganese dioxide is added to potassium chlorate and heated it decomposes to give potassium chloride and oxygen.(c) When dilute acetic acid is poured on baking soda, a strong effervescence is observed. The products formed are sodium acetate, water and carbon dioxide.(d) A white precipitate is formed when an aqueous solution of sodium chloride is mixed with an aqueous solution of silver nitrate. The products formed are silver chloride and sodium nitrate.(e) A strong pungent smelling gas is evolved when ammonium chloride is heated with sodium hydroxide. The products formed are sodium chloride, water and ammonia gas.(f) A large amount of heat energy is evolved when water is added to quick lime. The product formed is calcium hydroxide.

Question 5

Question 6What information do you get from the equationH2 + Cl2 ⟶ 2HCl?

Accepted Answer

We get the following information from the given chemical equation:Hydrogen and Chlorine are reactants.The reaction is irreversible.The product formed is hydrochloric acid.The equation is balanced i.e. number of atoms of each element on reactants and products sides are equal.

Question 6

Question 4Give a balanced equation for addition of iron to copper [II] sulphate solution. State the change in color seen.

Accepted Answer

CuSO4Blue+Fe⟶FeSO4Light green+CuBrownish red\underset{	ext{Blue}}{	ext{CuSO}_4} + 	ext{Fe} \longrightarrow \underset{	ext{Light green}}{	ext{FeSO}_4} + \underset{	ext{Brownish red}}{	ext{Cu}}BlueCuSO4​​+Fe⟶Light greenFeSO4​​+Brownish redCu​Colour changes from blue to light green.

Question 7

Question 7In certain reactions an insoluble solid called precipitate is formed. State the colour and name of the precipitate formed in each of the following reactions involving addition of:(a) Dilute hydrochloric acid to silver nitrate(b) Iron [II] sulphate to sodium hydroxide(c) Iron [III] chloride to ammonium hydroxide(d) Copper [II] sulphate to sodium hydroxide(e) Lead nitrate to ammonium hydroxide

Accepted Answer

S.No.Name ofprecipitateColour ofprecipitate(a)Silver ChlorideMilky White(b)Iron [II] hydroxideDirty Green(c)Iron [III] hydroxideReddish Brown(d)Copper [II] hydroxidePale Blue(e)Lead hydroxideChalky White

Question 8

Question 8Give examples of exothermic reactions i.e. heat evolved in each of the following:(a) reaction between a solid and a liquid(b) reaction between two gasesGive two examples of exothermic reactions seen in everyday life.

Accepted Answer

(a) CaO + H2O ⟶ Ca(OH)2 + Δ(b) 2H2 + O2 ⟶ 2H2O + ΔTwo examples of exothermic reactions from everyday life are:Human Body — Many chemical reactions in our body are exothermic and provide energy to survive.Setting of Cement — Cement setting liberates heat hence concrete structures are set slowly.

Question 9

Question 9Give one example in each case where supplying energy [given below] is necessary for a chemical reaction.(a) Heat energy(b) Light energy(c) Electrical energy(d) Pressure(e) Catalyst

Accepted Answer

(a) ZnCO3 →Δ\xrightarrow{\Delta}Δ​ ZnO + CO2 [g](b) H2 + Cl2 →sunlight\xrightarrow{	ext{sunlight}}sunlight​ 2HCl(c) 2H2O→currentelectric2H2+O22	ext{H}_2	ext{O} \xrightarrow[	ext{current}]{	ext{electric}} 2	ext{H}_2 + 	ext{O}_22H2​Oelectriccurrent​2H2​+O2​(d) N2+3H2⇌450°C Fe/200 atmos press2NH3	ext{N}_2 + 3	ext{H}_2 \xrightleftharpoons [450	ext{\degree C }]{	ext{Fe/200 atmos press}} 2	ext{NH}_3N2​+3H2​Fe/200 atmos press450°C ​2NH3​ + Δ(e) 4NH3 + 5O2 →Pt-800 °C\xrightarrow{	ext{Pt-800 \degree C}}Pt-800 °C​ 4NO + 6H2O + Δ

Question 10

Question 10Representation of the results of a chemical change – is a chemical equation.For the equation: FeCl3 + 3NH4OH ⟶ 3NH4Cl + Fe(OH)3 ↓Answer the following:(a) Write the word equation for the above molecular equation.(b) Is the equation given above a balanced equation. Give reasons.(c) Name the reactants and the products in the above equation.(d) What is the indications of the arrow between the reactants and the products and of the arrow pointing downwards at the end.

Accepted Answer

(a) Iron (III) chloride + ammonium hydroxide ⟶ Ammonium chloride + Iron (III) hydroxide(b) In the given equation:ReactantsProducts1 atom of iron [Fe]1 atom of iron [Fe]3 atoms of chlorine [Cl]3 atoms of chlorine [Cl]3 atoms of nitrogen [N]3 atoms of nitrogen [N]15 atoms of hydrogen [H]15 atoms of hydrogen [H]3 atoms of oxygen [O]3 atoms of oxygen [O]As, the number of atoms of each element of reactants = the number of atoms of each element of products. Hence, the equation is balanced.(c) Reactants – Iron (III) Chloride [FeCl3 ] and Ammonium hydroxide [3NH4OH],Products – Ammonium Chloride [3NH4Cl] and Iron (III) Hydroxide [Fe(OH)3].(d) The arrow between reactants and products indicates the chemical reaction taking place in the forward direction i.e., reaction is taking place between reactants and as a result products are formed. The arrow pointing downwards indicates formation of precipitate.

Question 11

Question 11Give word equations for the following chemical reactions and give the names of the products formed.(a) Zn + 2HCl ⟶ ZnCl2 + H2(b) CuO + H2SO4 ⟶ CuSO4 + H2O(c) Zn + S ⟶ ZnS(d) ZnCO3 →Δ\xrightarrow{\Delta}Δ​ ZnO + CO2(e) NH3 + HCl ⟶ NH4Cl

Accepted Answer

(a) Zinc + dilute Hydrochloric acid ⟶ Zinc chloride + HydrogenThe products formed are zinc chloride and hydrogen.(b) Copper (II) oxide + Sulphuric Acid ⟶ Copper (II) sulphate + waterThe products formed are Copper (II) sulphate and water(c) Zinc + Sulphur ⟶ Zinc SulphideThe product formed is Zinc Sulphide.(d) Zinc carbonate ⟶ Zinc oxide + Carbon dioxideThe products formed are Zinc oxide and Carbon dioxide(e) Ammonia + Hydrogen chloride ⟶ Ammonium chlorideThe product formed is Ammonium chloride.

Language of Chemistry

Exercise

Language of Chemistry