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vidyapeeth-logo           MOLE CONCEPT PART F

Exercise – 1

MOLE-I : Basic Definitions and Chemical Formulae

Section (A) : Basic definitions, Atomic mass unit, NA & Mole, Moles of atoms and molecules

A-1. Find the total number of H, S and ‘0’ atoms in the following :

(a) 196 gm H2SO4                                                           (b) 196 amu H2SO4

(c) 5 mole H2S208                                                                    (d) 3 molecules H2S206 .

A-2               If, from 10 moles NH3 and 5 moles of H2SO4 , all the H-atoms are removed in order to form H2 gas, then fi-: the number of H2 molecules formed.

A-3               If from 3 moles MgSO4.7H20. all the ‘0’ atoms are taken out and converted into ozone find the number of molecules formed.

Section (B) : Laws of chemical combination, Molar volume of ideal gases at STP, Average molar mass

B-1         Two compounds each containing only tin and oxygen had the following composition :

Mass % of tin                                   Mass % of oxygen

Compound A                    78.77                                                             21.23

Compound B                    88.12                                                             11.88

Show these data illustrate the law of multiple proportions.

B-2         The measured density at N.T.P. of a gaseous sample of a compound was found to be 1.20 g/liter. What weight of 1 mole of the gaseous sample.

B-3         Three oxides of nitrogen N20, NO2 and N2C3 are mixed in a molar ratio of 3 : 2 : 1. Find the average rr mass of gaseous mixture.

Section (C) : Empirical Formula, % Composition of a given compound by mass, % By mole, Minimum molecular mass determination.

C-1        A compound contains 25% hydrogen and 75% carbon by mass. Determine the empirical formula of the compound.

C-2        In a gaseous mixture 2mol of 002. 1 mol of H2 and 2 mol of He are present than determine mole percentage of CO2.

C-3        A compound has haemoglobin like structure. It has one Fe. It contain 4.6% of Fe. Determine its approximate molecular mass.

MOLE-II : Basic Stoichiometry :

Section (D) : Stoichiometry, Equation based calculations (Elementary level single equation or 2)

0-1. Calculate the residue obtained on strongly heating 2.76 g Ag2003.


Ag2CO3__________ 2Ag + 002 + —2 02

D-2       Calculate the weight of iron which will be converted into its oxide by the action of 18g of steam.

Unbalanced reaction : Fe + H2O ________ > Fe304 + H2.

D-3       A sample of KCIO3 on decomposition yielded 448 mt.. of oxygen gas at NTP. Calculate

(i)  Weight of oxygen product,

(ii) Weight of KCIO3 originally taken, and

(iii)Weight of KCI produced.                 (K = 39 , CI = 35.5 and 0 = 16)

Section (E) : Limiting reagent, % Excess, % Yield I Efficiency

E-1. 50 g of CaCO3 is allowed to react with 73.5 g of H3PO4. Calculate :

(i) Amount of Ca3(PO4)2 formed (in moles)

(ii)   Amount of unreacted reagent (in moles)

E-2. Carbon disulphide, 032, can be made from by-product 302. The overall reaction is

5C + 2302 _____ > 032 + 400

How much CS2 can be produced from 440 kg of waste SO2 with 60 kg of coke if the SO2 conversion is 80%?

E-3. The percent yield for the following reaction carried out in carbon tetrachloride (0014) solution is 80%

Br2 + C12___________ > 2BrCI

(a) What amount of Br0I would be formed from the reaction of 0.025 mol Br2 and 0.025 mol Cl2?

(b) What amoumt of Br2 is left unchanged?

Section (F) : Principle of atom conservation (POAC), Reactions in sequence & parallel, Mixture analysis, % Purity

F.I.   What amount of CaO will be produced by 1 g of Calcium ?

F-2. The following process has been used to obtain iodine from oil-field brines in California.

Nal + AgNO3 2Fe12 + 3012

_ > Agl + NaNO3

_ > 2FeCI3 + 212
2Agl + Fe                     Fe12 + 2Ag

How many grams of AgNO3 are required in the first step for every 254 kg I, produced in the third step.

F-3. KCIO3 decomposes by two parallel reaction


(i)  2KCIO3      –> 2KCI + 302

(ii) 4KCI03    A        3KCI04 + KCI

If 3 moles of 02 and 1 mol of KCIO4 is produced along with other products then determine initial moles of KCI03.

F-4. A 2 gm sample containing Na2CO3 and NaHCO3 losses 0.248 g when heated to 3000 C , the temperature at

which NaHCO3 decomposes to Na2CO3 , CO2 and H20. What is the percentage of Na2CO3 in the giver mixture ?     (Na = 23 , C = 12 0 = 16 and H = 1)

MOLE-Ill : Oxidation Reduction & Balancing Redox Equations :

Section (G) : Basics of oxidation number

G-1. Calculate the oxidation number of underlined elements in the following compounds :

(a) K[Co(C204)2(NH3)2]                                         (b) K4P207                            (c) CrO2C12

(d) Na2[Fe(CN)5(NO+)]                                        (e) Mn304                                 (f) Ca(CIO2)2

(g) [Fe(NO+) (H20)5]SO4                      (h) Zn022-                                (i) Fec, 930

G-2.          Identify the oxidant and the reductant in the following reactions :

(a) KMn04 + KCI + H2SO4 _______ > MnSO4 + K2SO4 + H2O + Cl2

(b) FeCl2 + H202 + HCI _______ –> FeCI3 + H2O

(c) Cu + HNO3 (dil) ____ > Cu (NO3)2 + H2O + NO

(d) Na2HAs03 + KBrO3 + HCI ____ ) NaCI + KBr + H3AsO4

(e) 12 + Na2S203 ______ > Na2S406 + Nal

Section (H) : Balancing redox reactions

H-1. Write balanced net ionic equations for the following reactions in acidic solution :

(a) S4062-(aq) + Al(s) ___ > H2S(aq) + Al3+(aq)

(b) S2032-(aq) + Cr2072-(aq) ____ > S4062-(aq) + Cr3+(aq)

(c) CI03- (aq) + As2S3(s) ______ -> C1—(aq) + H2As04 (aq) + HSO4(aq)

(d) I03 (aq)+ Re(s) ___ > Re04 (aq) + I(aq)

(e) HSO4—(aq) + As4(s) + Pb304(s) ______ > PbSO4(s) + H2As04 (aq)

(f)  HNO2(aq) ____ > NO3 + NO(g)

H-2. Write balanced net ionic equations for the following reactions in basic solution :

(a) C4H4062-(aq) + CI03(aq) _____ > CO32-(aq) + C1 (aq)

(b) Al(s) + BiONO3(s) _____ > Bi(s) + NH3(aq) + [Al(OH)4] (aq)

(c) H202(aq) + C1207(aq) ___ > C102 (aq) + 02(g)

(d) TI203(s) + NH2OH(aq) ___ > TIOH(s) + N2(g)

(e) [Cu(NH3)4]2+ (aq) + S2042-(aq) ________ > S032-(aq) + Cu(s) + NH3(aq)

(f)  Mn(OH)2(s) + Mn04 (aq) ___ > Mn02(s)

MOLE-IV : Concentration Measurement :

Section (I) Units of concentration measurement, Interconversion of concentration units

I-1. Find the mass of KOH needed to prepare 100 ml 1 M KOH solution. [At. mass K = 39]

1-2. How much NaNO3 must be weighed out to make 50 ml of an aqueous solution containing 70 mg of N

per mL ?

1-3. (i) If you are given a 2M NaOH solution having density 1 gm/ml, then find the molality of solution.

(ii)   Find the molarity of 5m (molal) NaOH solution having density 1.5 gm/ml.

(iii)  Find the mole fraction of solute in problem (i)

(iv)  Find the mole fraction of solute in problem (ii)

(v)   Find the % (w/w) of NaOH in solution in problem (i)

(vi)  Find the % (w/w) of NaOH in solution in problem (ii) (vii)Find the % (w/v) of NaOH in solution in problem (ii)

(viii)    A 300 gm, 30% (w/w) NaOH solution is mixed with 500 gm 40% (w/w) NaOH solution. Find the mass percentage

(w/w) of final solution.

(ix)      What is % (w/v) NaOH in problem (viii) if density of final solution is 2 gm/ml ?

(x) What is the molality of final solution obtained in problem (viii) ?

Section (J) : Dilution & Mixing of two liquids

J-1              Find the Cl- concentration in solution which is obtained by mixing one mole each of BaCl2, NaCI and HCI in 500
ml water.

J-2              What volume of water should be added to 50 ml of HNO3 having density 1.5 g m1-1 and 63.0% by weight to
have one molar solution.

J-3              What maximum volume of 3 M solution of KOH can be prepared from 1 L each of 1 M KOH and 6 M KOH
solutions by using water ?

MOLE-I : Basic Definitions and Chemical Formulae
Marked Questions may have more than one correct option.

Section (A) : Basic definitions, Atomic mass unit, NA & Mole, Moles of atoms and molecules

A-1. The modern atomic weight scale is based on :

(A) C12                                     (B) 016                                    (C) H1                                    (D) N14

Which of the following expressions is correct (n = no. of moles of the gas, NA = Avogadro constant, m = mass of 1 molecule of the gas, N = no. of molecules of the gas)?

(A) n = m NA                         (B) m = NA                            (C) N = nNA                      (D) m = mn/NA

The charge on 1 gram ions of Ar is : (NA = Avogadro number, e = charge on one electron)

1                                 1                                1

(A)               NAe coulomb     (B)       x NAe coulomb (C) 9 x NAe coulomb (D) 3 x NAe coulomb

L.4 Which of the following contains the greatest number of atoms ?

(A) 1.0 g of butane (C4H10)                                                    (B) 1.0 g of nitrogen (N2)

(C) 1.0 g of silver (Ag)                                                            (D) 1.0 g of water (H20)

1.5 A gaseous mixture contains CO2(g) and N20(g) in 2 : 5 ratio by mass. The ratio of the number of molecules of

CO2(g) and N20(g) is :

(A) 5 :2                                  (B) 2 : 5                                 (C) 1 : 2                              (D) 5 : 4

The weight of a molecule of the compound C60H22 is

A) 1.09 x 10-21g                   (B) 1.24 x 10-21g                   (C) 5.025 x 10-23g                  (ID) 16.023 x 10-23g

Section (B) : Laws of chemical combination, Molar volume of ideal gases at STP, Average molar mass

our 1-1 litre flasks are separately filled with the gases H2, He, 02 and 03 at the same temperature and cressure. The ratio of total number of atoms of these gases present in different flask would be :

A) 1 : 1 : 1 : 1                      (B) 1 : 2 : 2 : 3                     (C) 2 : 1 : 2 : 3                     (D) 3 : 2 : 2 : 1

B-2.  Under the same conditions, two gases have the same number of molecules. They must

(A) be noble gases                                         (B) have equal volumes

(C) have a volume of 22.4 dm’ each               (D) have an equal number of atoms

B-3 3g of a hydrocarbon on combustion in excess of oxygen produces 8.8 g of CO2 and 5.4 g of H20. The

illustrates the law of

(A) conservation of mass                               (B) multiple proportions

(C) constant proportions                                (D) none of these

B-4. 16 g of an ideal gas SOX occupies 5.6 L. at STP. The value of x is

(A) x = 3                        (B) x = 2                     (C) x = 4                     (D) none

B-5  Boron has two stable isotopes, 1°B (relative abundance = 19%) and 11B (relative abundance = 81% ). –

atomic mass (in amu) that should appear for boron in the periodic table is :

(A) 10.8                         (B) 10.2                      (C) 11.2                                 (D) 10.6

Section (C) : Empirical Formula, % Composition of a given compound by mass, % By mole Minimum molecular mass determination.

The empirical formula of a compound of molecular mass 120 is CH2O. The molecular formula of the corripc..-: is

(A) C2H402                                (B) 04H804                   (C) 031-1603                         (D) all of these

C-2. Calculate the molecular formula of compound which contains 20% Ca and 80% Br (by wt.) if molecular wei

of compound is 200. (Atomic wt. Ca = 40, Br = 80)

(A) Ca12Br                      (B) CaBr2                    (C) CaBr                      (D) Ca2Br

C-3.*_ Which is/are correct statements about 1.7 gm of NH3

(A) It contain 0.3 mol H – atom                        (B) it contain 2.408 x 102′ atoms

(C) Mass % of hydrogen is 17.65%                (D) It contains 0.3 mol N-atom

C-4 A compound possess 8% sulphur by mass. The least molecular mass is :

(A) 200                          (B) 400                       (0) 155                        (D) 355

C-5.     Cortisone is a molecular substance containing 21 atoms of carbon per molecule. The mass percentage :-

carbon in cortisone is 69.98%. Its molar mass is :

(A) 176.5                       (B) 252.2                     (0) 287.6                              (D) 360.1


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