Question 1

Question 1State the meaning of the term –(a) atom(b) molecule(c) radical – with a suitable example.

Accepted Answer

(a) Atom — An atom is the smallest particle of an element that exhibits all the properties of that element. It may or may not exist independently but takes part in every chemical reactions.Example : O — Oxygen atom, H — Hydrogen atom(b) Molecule — A molecule is the smallest particle of an element or compound, made up of two or more atoms of an element or compound which has independent existence exhibiting all of their properties.Example : O2 — Oxygen molecule, H2O — Water molecule(c) Radical — A radical is an atom of an element or a group of atoms of different elements that behaves as a single unit with a positive or negative charge on it.Example : NH4+ — Ammonium radical

Question 2

Question 2Draw the basic structure of an atom representing its –(a) Subatomic particles(b) Nucleus(c) Orbits or shells.

Accepted Answer

Below labelled diagram shows the basic structure of an atom:

Question 3

Question 6Explain the term – 'atomicity'. Give a reason why –(a) Helium is considered monoatomic, but hydrogen a diatomic molecule.(b) Ozone is considered triatomic, but phosphorus a tetratomic molecule.

Accepted Answer

Atomicity — It is the number of atoms present in a molecule of an element.(a) Helium (He) is considered monoatomic because it contains only one atom of helium while hydrogen contains two atom of hydrogen (H2) therefore it is considered a diatomic molecule.(b) Ozone is considered triatomic because it is composed of three atoms of Oxygen (O3) while phosphorous is composed of four atoms (P4), therefore, it is considered a tetratomic molecule.

Question 4

Question 8'A radical takes part — unsplit in a chemical reaction and retains its identity in reactions'. With reference to the radical:(a) ammonium(b) bisulphate(c) carbonate — state the group of atoms present in each radical.

Accepted Answer

(a) Ammonium [NH4]: 1 nitrogen atom and 4 hydrogen atoms(b) Bisulphate [HSO4]: 1 hydrogen atom, 1 sulphur atom and four oxygen atoms(c) Carbonate [CO3] : 1 carbon atom and 3 oxygen atoms

Question 5

Question 9Differentiate between the following with suitable examples — A basic radical and a acid radical.

Accepted Answer

Basic radicalAcid radicalIt is a radical which behaves like hydrogen or a metal in a chemical reaction.It is a radical which behaves like a non-metal in a chemical reaction.The positive part of a compound is called the basic radical.The negative part of a compound is called the acid radical.Example:In Sodium nitrate, Na+ is the basic radical.Example:In Sodium nitrate, NO3- is the acid radical.

Question 6

Question 11Explain the term – 'valency'. State giving reasons the valency of –(a) chlorine in hydrogen chloride(b) sulphate in sulphuric acid(c) nitrogen in ammonia(d) magnesium in magnesium oxide

Accepted Answer

Valency of an element or radical is the number of hydrogen atoms which can combine with or displace one atom of the element or radical forming a compound.(a) One atom of hydrogen combines with one atom of chlorine to form HCl, hence the valency of chlorine in hydrogen chloride is 1-.(b) Two atoms of hydrogen combine with one radical of sulphate to form sulphuric acid (H2SO4), hence the valency of sulphate in sulphuric acid is 2-.(c) Three atoms of hydrogen combine with one atom of nitrogen to form ammonia (NH3) hence the valency of nitrogen in ammonia is 3-.(d) We know that valency of oxygen is 2-. Hence, in magnesium oxide [MgO], valency of magnesium is 2+.

Question 7

Question 12Give the symbol and valency of the following elements and radicals.(a) Potassium(b) Sodium(c) Hydrogen(d) Calcium(e) Aluminum(f) Magnesium(g) Zinc(h) Chlorine [chloride](i) Sulphur [sulphide](j) Nitrogen [nitride](k) Oxygen [oxide](l) Ammonium(m) Bicarbonate(n) Nitrate(o) Bisulphate(p) Bisulphite(q) Hydroxide(r) Carbonate(s) Sulphate(t) Sulphite

Accepted Answer

S.No.Element/RadicalsSymbolValency(a)PotassiumK++1(b)SodiumNa++1(c)HydrogenH++1 or -1(d)CalciumCa2++2(e)AluminiumAl3++3(f)MagnesiumMg2++2(g)ZincZn2++2(h)Chlorine [chloride]Cl--1(i)Sulphur [sulphide]S2--2(j)Nitrogen [nitride]N3--3(k)Oxygen [oxide]O2--2(l)AmmoniumNH4++1(m)BicarbonateHCO3--1(n)NitrateNO3--1(o)BisulphateHSO4--1(p)BisulphiteHSO3--1(q)HydroxideOH--1(r)CarbonateCO32--2(s)SulphateSO42--2(t)SulphiteSO32--2

Question 8

Question 13Give an example of three elements exhibiting variable valency.

Accepted Answer

Three elements exhibiting variable valency are:Iron (Fe) can show a valency of 2 and 3.Copper (Cu) can show a valency of 1 and 2.Lead (Pb) can show a valency of 2 and 4.

Question 9

Question 14State what is meant by the term – chemical formula. Give the chemical formula of –(a) sodium hydroxide(b) sodium nitrate(c) sodium bicarbonate(d) sodium sulphite(e) magnesium nitrate(f) ammonium sulphate(g) carbonic acid(h) calcium phosphate

Accepted Answer

Chemical formula is the representation of a substance by means of symbols. It denotes in a compound, the number of atoms of each element present.(a) Sodium hydroxideNa1+↗OH1−Na11 ↘↙ OH1⇒Na1 ↘↙ OH1\text{Na}^{1+} \phantom{\nearrow} \text{OH}^{1-} \[0.5em] \overset{\phantom{1}{1}}{\text{Na}} \space {\searrow}\mathllap{\swarrow} \space \overset{1}{\text{OH}} \Rightarrow \underset{\phantom{}1{}}{\text{Na}} \space {\searrow}\mathllap{\swarrow} \space \underset{1}{\text{OH}} \[0.5em]Na1+↗OH1−Na11 ↘↙ OH1⇒1Na​ ↘↙ 1OH​So, we get the formula as NaOH\bold{Na}\bold{OH}NaOH(b) Sodium nitrateNa1+↗NO31−Na11 ↘↙ NO31⇒Na1 ↘↙ NO31\text{Na}^{1+} \phantom{\nearrow} \text{NO}_3^{1-} \[0.5em] \overset{\phantom{1}{1}}{\text{Na}} \space {\searrow}\mathllap{\swarrow} \space \overset{1}{\text{NO}_3} \Rightarrow \underset{\phantom{}1{}}{\text{Na}} \space {\searrow}\mathllap{\swarrow} \space \underset{1}{\text{NO}_3} \[0.5em]Na1+↗NO31−​Na11 ↘↙ NO3​1​⇒1Na​ ↘↙ 1NO3​​So, we get the formula as NaNO3\bold{Na}\bold{NO}_3NaNO3​(c) Sodium bicarbonateNa1+↗HCO31−Na11 ↘↙ HCO31⇒Na1 ↘↙ HCO31\text{Na}^{1+} \phantom{\nearrow} \text{HCO}_3^{1-} \[0.5em] \overset{\phantom{1}{1}}{\text{Na}} \space {\searrow}\mathllap{\swarrow} \space \overset{1}{\text{HCO}_3} \Rightarrow \underset{\phantom{}1{}}{\text{Na}} \space {\searrow}\mathllap{\swarrow} \space \underset{1}{\text{HCO}_3} \[0.5em]Na1+↗HCO31−​Na11 ↘↙ HCO3​1​⇒1Na​ ↘↙ 1HCO3​​So, we get the formula as NaHCO3\bold{Na}\bold{HCO}_3NaHCO3​(d) Sodium sulphiteNa1+↗SO32−Na11 ↘↙ SO32⇒Na2 ↘↙ SO31\text{Na}^{1+} \phantom{\nearrow} \text{SO}_3^{2-} \[0.5em] \overset{\phantom{1}{1}}{\text{Na}} \space {\searrow}\mathllap{\swarrow} \space \overset{2}{\text{SO}_3} \Rightarrow \underset{\phantom{}2{}}{\text{Na}} \space {\searrow}\mathllap{\swarrow} \space \underset{1}{\text{SO}_3} \[0.5em]Na1+↗SO32−​Na11 ↘↙ SO3​2​⇒2Na​ ↘↙ 1SO3​​So, we get the formula as Na2SO3\bold{Na}_2\bold{SO}_3Na2​SO3​(e) Magnesium nitrateMg2+↗NO31−Mg12 ↘↙ NO31⇒Mg21 ↘↙ NO32\text{Mg}^{2+} \phantom{\nearrow} \text{NO}_3^{1-} \[0.5em] \overset{\phantom{1}{2}}{\text{Mg}} \space {\searrow}\mathllap{\swarrow} \space \overset{1}{\text{NO}_3} \Rightarrow \underset{\phantom{2}{1}}{\text{Mg}} \space {\searrow}\mathllap{\swarrow} \space \underset{2}{\text{NO}_3} \[0.5em]Mg2+↗NO31−​Mg12​ ↘↙ NO3​1​⇒21Mg​ ↘↙ 2NO3​​So, we get the formula as Mg(NO3)2\bold{Mg}\bold{(NO}_3)_2Mg(NO3​)2​(f) Ammonium sulphateNH41+↗SO42−NH411 ↘↙ SO42⇒NH422 ↘↙ SO41\text{NH}_4^{1+} \phantom{\nearrow} \text{SO}_4^{2-} \[0.5em] \overset{\phantom{1}{1}}{\text{NH}_4} \space {\searrow}\mathllap{\swarrow} \space \overset{2}{\text{SO}_4} \Rightarrow \underset{\phantom{2}{2}}{\text{NH}_4} \space {\searrow}\mathllap{\swarrow} \space \underset{1}{\text{SO}_4} \[0.5em]NH41+​↗SO42−​NH4​11​ ↘↙ SO4​2​⇒22NH4​​ ↘↙ 1SO4​​So, we get the formula as (NH4)2SO4\bold{(NH}_4)_2\bold{SO}_4(NH4​)2​SO4​(g) Carbonic acidH1+↗CO32−H11 ↘↙ CO32⇒H22 ↘↙ CO31\text{H}^{1+} \phantom{\nearrow} \text{CO}_3^{2-} \[0.5em] \overset{\phantom{1}{1}}{\text{H}} \space {\searrow}\mathllap{\swarrow} \space \overset{2}{\text{CO}_3} \Rightarrow \underset{\phantom{2}{2}}{\text{H}} \space {\searrow}\mathllap{\swarrow} \space \underset{1}{\text{CO}_3} \[0.5em]H1+↗CO32−​H11 ↘↙ CO3​2​⇒22H​ ↘↙ 1CO3​​ So, we get the formula as H2CO3\bold{H}_2\bold{CO}_3H2​CO3​(h) Calcium phosphateCa2+↗PO43−Ca12 ↘↙ PO43⇒Ca23 ↘↙ PO42\text{Ca}^{2+} \phantom{\nearrow} \text{PO}_4^{3-} \[0.5em] \overset{\phantom{1}{2}}{\text{Ca}} \space {\searrow}\mathllap{\swarrow} \space \overset{3}{\text{PO}_4} \Rightarrow \underset{\phantom{2}{3}}{\text{Ca}} \space {\searrow}\mathllap{\swarrow} \space \underset{2}{\text{PO}_4} \[0.5em]Ca2+↗PO43−​Ca12 ↘↙ PO4​3​⇒23Ca​ ↘↙ 2PO4​​So, we get the formula as Ca3(PO4)2\bold{Ca}_\bold{3}\bold{(PO_4)_2}Ca3​(PO4​)2​

Question 10

Question 15'Dilute hydrochloric acid is added to sodium hydroxide'. Give a word equation and a molecular equation of the same. Is the equation written, a balanced equation. Give reasons.

Accepted Answer

Word equation:Sodium hydroxide + hydrochloric acid ⟶ sodium chloride + waterMolecular equation:NaOH + HCl ⟶ NaCl + H2OIn the above equation,ReactantsProducts1 atom of sodium [Na]1 atom of sodium [Na]1 atom of oxygen [O]1 atom of oxygen [O]1 atom of chlorine [Cl]1 atom of chlorine [Cl]2 atoms of hydrogen [H]2 atoms of hydrogen [H]As, the number of atoms of each element of reactants = the number of atoms of each element of products. Hence, the equation is balanced.

Question 11

Question 16State what the group number in the Modern Periodic Table signifies. Give a reason why elements in the same group, have similar valency and similar chemical properties.

Accepted Answer

Group number signifies the number of electrons in the outer shell of an atom of the element.As the number of electrons in the outer shell of all elements in a group is the same. Hence all elements in the same group of the periodic table have same valency and similar chemical properties.

Question 12

Question 4Write the symbols and valencies of the following radicals:(a) Magnesium ion(b) Ammonium(c) Carbonate(d) Nitrate(e) Oxide(f) Bisulphate(g) Aluminium ion

Accepted Answer

RadicalsSymbolsValencyMagnesium ionMg2+2AmmoniumNH4+1CarbonateCO32-2NitrateNO3-1OxideO2-2BisulphateHSO4-1AluminiumAl3+3

Question 13

Question 6bName one ion for each of the valencies -1, -2 and -3.

Accepted Answer

Fluoride ion (F-) has valency -1.Sulphide ion (S2-) has valency -2.Nitride ion (N3-) has valency -3.

Question 14

Question 9Write the molecular formula of:(a) Sodium sulphide(b) Magnesium oxide(c) Calcium hydroxide(d) Hydrogen chloride(e) Sulphuric acid(f) Iron (II) sulphide(g) Iron (III) sulphate(h) Nitric acid(i) Calcium phosphate(j) Aluminium sulphate(k) Magnesium nitride

Accepted Answer

(a) Na2S(b) MgO(c) Ca(OH)2(d) HCl(e) H2SO4(f) FeS(g) Fe2(SO4)3(h) HNO3(i) Ca3(PO4)2(j) Al2(SO4)3(k) Mg3N2

Question 15

Question 3Match the radicals in List I with their correct names from List II.List IList II1. NO31-A: Bisulphite2. HSO41-B: Phosphate3. SO42-C: Carbonate4. PO43-D: Nitrite5. HCO31-E: Bicarbonate  F: Sulphate  G: Nitrate  H: Phosphite  I: Sulphite  J: Bisulphate

Accepted Answer

List IList II1. NO31-G: Nitrate2. HSO41-J: Bisulphate3. SO42-F: Sulphate4. PO43-B: Phosphate5. HCO31-E: Bicarbonate

Question 16

Question 5Name the followingA molecule of a compound containing two oxygen atoms and one nitrogen atom.The radical containing one nitrogen and four hydrogen atoms.The compound formed when iron [Fe2+] combines with oxygen [O2-].The group of the Modern Periodic Table to which calcium [Ca2+] belongs.A non-metal which forms a polyatomic molecule with more than three atoms.

Accepted Answer

Nitrogen dioxide [NO2]Ammonium [NH4]Iron (II) oxide [FeO]Group 2Phosphorous (P4)

Atomic Structure

Atomic Structure

Exercise

Objective Type Questions