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### 4.- Mole.

posted Mar 25, 2016, 11:46 AM by Upali Salpadoru   [ updated Aug 29, 2019, 8:26 PM ]
Mole

What is a mole?

The ‘mole’ is the SI unit for the measurement of large numbers of minute particles.

Number of particles in 1 mol is

6.02 x 1023     …….

Symbol =AN.

= 602,000,000,000,000,000,000,000.

Fig.1 Mass of a mole.

 Avagadoro number:- Avogadro number is equal to the number of atoms in 12 grams of the isotope  Carbon-12

A simple way to look at it.

If you take the atomic mass of any element measured in grams it can be considered as

1 mole of atoms..

Or

If you take the molecular mass of a chemical in grams, it will have 1 mole of molecules.

Similarly you can take one mole of cat-ions or an-ions and even a mole of photons.

•   The symbol for mole is - 'mol'.

Table 1.

This table gives the mass of 1 mole of some elements and the number of particles in each..

 Atom C O S Cl Pb Mass 12 g 16 g 32 g 35.5 g 207 No. of Atoms. AN AN AN AN AN
AN = 6.02 x 1023

Table 2.

This table gives the number of molecules in 1 mole.

 Molecule CO2 O2 SO2 Cl2 PbO Mass 44 g 32 g 64 g 71 g 223g # Molecules AN AN AN AN AN

Table 3.

This table gives the number of radicals in 1 mole.

 Radical H+ OH- SO4-- Mass of electrons is negligible Mass 1 g 17 g. 96 g. # Radicals AN AN AN

If you are fond of formulae:-  Molarity...."M'

This is a unit to show the strength or the concentration of solutions. This is usually given as the number of solute moles dissolved in a litre of a solution.

If one ltre of a salt NaCl , solution contains 1 mole of salt; (That is 58.5 g), its molarity will be 1 mol/L ( L for litre)

A few questions to practice.

1.0

 Question Answer 1.How many Carbon dioxide molecules are there in 22 g. of CO2? AN ÷  2 molecules. 2. What is the mass of 2 moles of PbO ? 446 g. 3.  What is the mass of 2 moles of Sulphur? 64 g. 4. What is the (real) mass of 1 Molecule of chlorine    Cl2  ? 71 ÷  AN   g. 5  What is the mass of one Atom of chlorine.  Cl ? 35.5 ÷  AN    g.

2.0

Let us tabulate some of these quantities for oxygen,  water and salt.

 Oxygen  O2 Water=H2O Salt =  NaCl Molar mass. 32 g. 18 g. 58.5g No.of moles in the given mass. 1 1 1 No. of molecules in the mass. AN …=…. 6.02x1023 6.02x1023 6.02x1023 No. of atoms in the mass. 2x 6.02x1023 3x6.02x1023 2x6.02x1023 Mass of 1 molecule 32/AN   g.. 18/AN   g.. 56.5/AN  g.

3.0
What is the molecular mole of Sulphur?
This is a difficult problem.  Sulphur has many types of molecules. The diagram gives a molecule with 8 atoms.

Normally  32 g /mol. is used for calculations.

Example 1

Find the no. of moles and the no. of molecules in    800g.. of anhydrous Copper sulphate.

Molar mass of CuSO4    =   64+ 32+ 64   =  160g./mol.

160 g.…………………………..1  mol.

800g …………………………   800/160   mol   =  5 mol.

1mol has……………………….AN molecules.

5 mol…………………………...5AN   molecules.

Example 2

If you have to weigh the no. of moles in column 1 of the chemicals in row 1 how many grams would you   weigh?

 No. of moles required. Sodium carbonateNa2CO3 Sodium hydroxide.NaOH. Calcium oxideCaO Magnesium sulphate.MgSO4 1 mol. 36+12+48=  96 g, 23+16+1=   40 g. 40.1 +16= 56,1g 24.3 +32+64=120.3 0.5 mol 92/2=48 g. 40/2 = 20 g. 28.1g, 60.15 g. 2 mol. 2x96 =192 g. 2x40= 80 g. 2x56.1=112.2g 2x120.3=240.6

Atomic Masses in alphabetical order. (Approximate)
 Atom Mass Atom Mass Atom Mass Atom Mass Atom Mass Atom Mass Ag 108 B 11 C 12.0 Fe 56 Li 7.0 P 31 Al 27 Ba 137 Ca 40 H 1 Mg 24 Pb 207 Ar 40 Be 9.0 Cd 112 He 4 Mn 54. S 32 Au 197 Br 80 Cl 35.5 Hg 201 N 14 Sn 119 Cu 64 I 127 Na 23 Si 26 Cr 52 O 16 Zn 119 K 39

1.0

Select the most suitable word for these:-.

A  Mole,   B- Avogadro’s number. C – Molar mass    D -  Mass of one molecule

E- Molarity ..

 1.Digital number of atoms in 12 grams of C-12 isotope. 2. A unit name for the molecular mass of water taken in grams. 3. What you get if you divide the relative a molecular mass  in grams by 6.02x1023? 4. Three times the molar mass of a chemical, taken in grams is dissolved to make  a litre of a solution. What is three in this case? 5. If this taken in grams there will AN   molecules.

=5 marks

2..0

 Question Answer 1)  If   a solution of  MgSO4 has 120 g dissolved in 500 ml. what is the molarity? 2)  What mass of sodium carbonate is necessary to make 250 ml. of a 1M solution 3)  If 100 ml  of a solution of CuSO4  gave a residue of 8 g of residue on evaporation, what was the concentration of the original solution. (Answer in mol/L) 4)  3M solution was diluted by adding an equal volume of distilled water. What probably is the Molarity of the new solution. 5)  A molar solution was evaporated , preventing any chemical changes due to heat. The readings were as follows:-   Original volume.........................100 ml   Volume after evaporation ............80 ml   What is the molarity of the  resulting solution?
2x5=10 marks.
3.0  Complete the blank spaces in this table.

 Formula Molar mass.g/mol. No. of molecules in a mole. Mass of 1 molecule in grams. No. of atoms in a molecule. Mass of an atom in grams. Oxygen O2 32g. Ozone.  O3 AN Iodine  I2 254/ AN White phosphorus P 1 31/AN

15. marks.

4.0

 Chemical formula Required mass. Mol No. of molecules. O2 i.………….. 4 mol. 4AN CO2 88g ii………….. iii……………. Ca(OH)2 iv………………… 0.5 mol. AN/2 Na2CO3.10(H2O) 572 g v……………... vi……………. C6H12O6 1.8g vii……………. viii…………….. Ag2Cr2O7 432g ix………..

2x9 = 18marks

5.0

1000 ml of a sodium carbonate solution was made using 106g. of solute.

1  How many moles of Na2CO3 are present in the solution?

2. If you measure out 22 ml of solution into a beaker, what is the molarity of that?

3.  How many moles can be obtained by evaporating 250ml of solution?

4.  What would be the mass of the residue after evaporating the water?

5.  What volume of the solution will have 0.1 moles?

5x5= 25 marks

6.0.

This question is regarding the Calcium chloride molecule. CaCl2.  Find the following.

4.1  Mass of 1 mol of the chemical compound?

4.2  The number of Ca++ ions in 1 mole of the compound.?

4.3  The number of Cl- ions in the  1 mole of the compound?

4x3=12 marks

7.0 This is the structure of Auric chloride. (Gold (III) chloride.

Considering the structural formula given answer the following:

1   Find the molar mass of the compound.

2   Find the mass of gold in 1 mole of the compound.

3  How many Au)+++ ions can you get from 1 mol of the compound?

4.  How many Cl-  ions can you get from 1 mole of the compound.

5.  Write an equation to show how the molecule can break up into ions.

3x5=15 marks

SOLUTIONS.

1.0

A  Mole,   B- Avogadro’s number. C – Molar mass    D -  Mass of one molecule

E- Molarity ..

 1.Digital number of atoms in 12 grams of C-12 isotope. B 2. A unit name for the molecular mass of water taken in grams. A 3. What you get if you divide the relative a molecular mass  in grams by 6.02x1023? D 4. Three times the molar mass of a chemical, taken in grams is dissolved to make  a litre of a solution. What is three in this case? E 5. If this taken in grams there will AN   molecules. C

2.0
 Question Answer 1)  If   a solution of  MgSO4 has 120 g dissolved in 500 ml. what is the molarity? 24+32+64=120500ml has120 g1000ml has 240g240g........2M. 2)  What mass of sodium carbonate Na2CO3is necessary to make 250 ml. of a 1M solution 46+ 12+48=106For 1000ml.....106gfor 250ml...... 26.5g. 3)  If 100 ml.  of a solution of CusO4  gave a residue of 8 g of residue on evaporation, what was the concentration of the original solution. (Answer in mol/L) 64+32+64=160100ml gave...8g1000 ml......80g M= 0.5mol/L. 4)  A 3M solution was diluted by adding an equal volume of distilled water. What probably is the Molarity of the new solution. When volume is doubled concentration should reduce to half.1/2 0f 3 = 1.5mol/L 5)  A molar solution was evaporated , preventing any chemical changes due to heat. The readings were as follows:-       Original volume.........................100 ml       Volume after evaporation ............80 ml       What is the molarity of the original solution and the resulting solution.. No. of moles in 100ml. original solution  = 1/10 moles.After evaporation 80 ml has =1/10 moles.1000ml will             have 0.1 x1000/801.25mol/L          orm1V1  = m2 V21 x100 = m 80m=  100/80  = 1.25 mol/L

3.0  Complete the blank spaces in this table.

 Formula Molar mass.g/mol. No. of molecules in a mole. Mass of 1 molecule in grams. No. of atoms in a molecule. Mass of an atom in grams. Oxygen O2 32g. AN 32/AN 2 32/2AN Ozone.  O3 48g. AN 48/AN 3 48/3AN Iodine  I2 254 g. AN 254/ AN 2 254/2AN White phosphorus P 31g AN 31/AN 1 31/AN

4.0
 Chemical formula Required mass. Mol No. of molecules. O2 i).32x4= 128 g 4 mol. 4AN CO2 88g ii) 88/44=2 mol. iii) 2AN Ca(OH)2 iv) 74 x0.5 = 37g 0.5 mol. AN/2 Na2CO3.10(H2O) 572 g v) 572/286= 2mol vi) 2AN C6H12O6 1.8g vii) 1.8/180=0.01 viii) 0.01AN Ag2Cr2O7 432g ix)432/432=1 mol.