by Chemistry department CHEM-111 General Chemistry Unit five (a) THE Mole بسم الله الرحمن الرحيم
Relationship among these terms
Stoichiometric calculations in chemical equations:
In chemistry, particles such as atoms, molecules, and ions are counted by the mole .
A mole: is a unit that contains 6.022 x 10 23 items (PARTICLES)
A mole is the amount of substance that chemists often use to measure chemicals.
One mole of an element is its relative atomic mass in grams.
example: C = 12, so one mole of carbon atoms weighs 12g.
The number of particles in one mole of a substance is 6.022 x 10 23 (Avogadro's number)
1 dozen = 12 objects
1 mole = 6.022 x 10 23 objects
C atom + O atom CO molecule
l mole C + l mole O 1mole CO
(6.022 x 10 23 atoms C) + (6.022 x 10 23 atoms O) (6.022 x 10 23 molecule CO)
Atomic or molecular mass (weight) of a substance expressed in grams.
Carbon Iron Fe C 6.022 X 10 23 atoms 1 mole of Fe atoms 55.78 g of Fe atoms 6.022 X 10 23 atoms 1 mole of C atoms 12.01 g of C atoms Avogadro’s Number (N) = 6.022 x 10 23 one mole of any element always contains Avogadro’s number of atoms 1 mole of an element is 6.022 X 10 23 atoms of that element
Avogadro’s Number, (N) Avogadro’s Number in 1 Mole = 6.022 x 10 23 particles Number of Particles in One-Mole Samples Substance Number and Types of Particles 1 mole sulphur 6.02 x 10 23 sulphur atoms 1 mole Hydrogen 6.02 x 10 23 Hydrogen atoms 1 mole water (H 2 O) 6.02 x 10 23 H 2 O molecules 1 mole NaCl 6.02 x 10 23 NaCl formula units 1 mole vitamin C, (C 6 H 8 O 6 ) 6.02 x 10 23 vitamin C molecules 1 mole of a compound is 6.022 X 10 23 of molecules or ions of that compound
Moles of Elements in Compounds
How many moles of each elements are present in 1 mole of caffeine ( C 8 H 10 N 4 O 2 )?
Answer: (C=8, H=10, N=4, O=2)
C 12 H 22 O 11 Moles of Elements in a Formula Sugar Carbon Hydrogen Oxygen 22 atoms H 22 moles H 11 atoms O 11 moles O 12 atoms C 12 moles C
Mole Calculations a. How many moles of chloride ions are in 3 moles of AlCl 3 ? Answer: 1 mole of AlCl 3 contains = 3 moles of Cl - ion 3 mole of AlCl 3 contains = 3 x 3 = 9 moles of Cl - particles or ion b . Find out number of moles of each element in two mole of Vitamin C (Ascorbic acid C 6 H 8 O 6 ) Answer: C= 12 ; H= 16 ; O = 12 . c. How many moles of carbon ,Hydrogen and Nitrogen are in 5 moles of quinine (C 20 H 24 N 2 O 2 )? Answer: C = 100; H = 120; N = 10; O = 10 ;
Conversion from Moles to grams
Amount of substance (m) = no of moles (n) x molar mass (M)
m = n x M
(6.02 x 10 23 particles = 1 mole)
Molar Mass The mass of one mole of pure substance is molar mass of that substance which is taken in grams . Number of moles x Atomic mass =Total mass or molar mass Molar mass of SO 3 : 1 mole S x 32.1g = 32.1g S 3 mole O x 16.0g = 48.0g O -------- Molar Mass of SO 3 = 80.1g Q: Calculate the molar mass of fructose, C 6 H 12 O 6 . [C=12, H=1.0, O=16] ( Answer = 180 g )
Conversion from Moles to grams
Calculate the grams of Ag (silver) in 4.65 moles of Ag. (Ag =107.9)
Amount of Ag = 4.65 x 107.9 = 501.73g
Amount of sub = no of moles x molar mass m = n x M or mass of Ag
What is mass of one atom of Ca? (6.02 x 10 23 atoms = 1 mol) 1 mol Ca =40.1 g Ca ( atomic mass) or 6.02 x 10 23 atoms of Ca have mass = 40.1g Avogadro’s Number & Mole Answer
Solve the following questions
1. How many grams does 0.500 moles of NaCl weigh? : [Na=23, Cl=35.5]
2. How many moles of Na 2 O are in its 231g? [ Na =23]
PERCENTAGE COMPOSITION of ELEMENTS IN COMPOUNDS What is % composition of chloroform CHCl 3 (an anesthetic)? Mol. Mass of CHCl 3 : 12.01 + 1.008 + 3 x 35.5 = 119.37 Similarly H = 0.844%, Cl = 89.09% Total = 99.99%
The symbolic representation of a chemical compound, which shows the number & kind of atoms.
H 2 O, CH 4 , NaCl, MgO, C 2 H 6 , , C 6 H 12 O 6 , N 2 O 4
Types of Chemical Formula
Empirical (experimental) Formula
A formula that gives the simplest whole number ratio of atoms in a formula unit.
H 2 O, CH 4 , NaCl, MgO, CH 2 , CH 2 O, NO 2.
A formula that describes the actual number of atoms in a molecule is molecular formula.
H 2 , H 2 O, CH 4 , C 2 H 4 , C 6 H 12 O 6, N 2 O 4 .
Empirical Formula of a colorless liquid is NO 2 , and has Molecular mass of 92. What is its Molecular formula?
Formula mass of NO 2 = 14 + 32 = 46,
[Atomic weight: N = 14, O = 16]
Given Molecular mass = 92
Number of times empirical formula occurs in compound:
Molecular Formula = Number of times x Empirical Formula
Molecular Formula = 2(NO 2 ) = N 2 O 4 (dinitrogen tetra oxide)
= 92/46 = 2 2) Molecular Formula Calculations
CHEMICAL FORMULAE FOR SIMPLE SUBSTANCES
Covalent Formula & Valency
The power of an element to combine with other element is valency.
In covalent compounds the number of unpaired electrons in an atom is its valency.
H 2 Cl 2 O 2 , N 2
Ionic Formula & Valency
The number of electrons lost or gained by an atom of element is its valency .
Loss of one electron Loss of Two electrons Gain of 1 electron Gain of 2 electrons
( Mostly for Covalent-compounds)
The sum of atomic masses of all atoms present in a molecule is its molecular mass
e.g. Mol. Mass of NH 3 = 1 x 14 + 3 x1 = 17
The sum of atomic masses of elements present in a formula unit ( group of ions).
NaCl, CaCl 2 , MgO, CaCO 3
e.g. Mass of NaCl=23 + 35.5 = 58.5
(Mostly for Ionic-compounds)
Mole Relationships in Chemical Equations
How many moles of CO 2 will be formed when 6 moles of propane burns?
C 3 H 8 + 5O 2 3CO 2 +4H 2 O
(Ans. =18 moles of CO 2 )
MOLE CONCEPT-CALCULATIONS How many moles of chlorine atoms are needed to combine with 6.4 mole of carbon to form C 2 Cl 6 . (Hexa-chloro ethane) 2C + 6Cl C 2 Cl 6 [Mole Ratio: 2:6] Calculation C Cl mole mole 2 6 6.4 ? = 6 x6.4 2 = 19. 2 moles of chlorine
Calculate the moles of Mg required to react with 3.50 mol of Cl to produce MgCl 2 .
Mg(1mol) + 2Cl(2mol) MgCl 2 (1mol)
2 moles of Cl combine with 1moles of Mg.
3.50 moles of Cl combine with ? moles of Mg.
Answer: 1.75 moles of Mg
How many moles of carbon atoms are needed to combine with 4.87 mol of chlorine to form C 2 Cl 6 . (Hexa-chloro ethane)
2C + 6Cl C 2 Cl 6 [Mole Ratio: 2:6]
Moles of C = = 1.62 moles.
Conversion from Grams to Moles
Calculate moles of S, in 40.5g of Sulfur. ( S=32)
Moles of S = 40.5/32 = 1.27 moles of S.
Calculations involving Grams
How many grams of O 2 are required to react
with 0.300mol of Al. ( O=16 ) ( AL=27)
4Al + 3O 2 2Al 2 O 3
Moles of O 2 ( required to react with 0.300 mol of Al) = 0.225 mol of O 2 Amount of O 2 = No of moles x Mol mass or m = n M = 0.225 x 32 = 7.20g of O 2 . Answer : 7.20g of O2
Calculations involving Grams
Calculate number of grams of Al 2 O 3 when 12.5g O 2. reacts completely with Al( Al=27)
(Ans = 26.6g Al)
4Al + 3O 2 2Al 2 O 3
Atomic or molecular mass of a substance expressed in grams is called: a) Avogadro’s number b) Mole c). Both a & b. The number of particles in one mole of a substance is 6.022 x 10 23 it is called: a) Avogadro’s number b) Mole c) Both a & b One mole of a substance contains 6.022 x 10 23 particles. a) True b) False Molar mass of SO 3 is: [S=32.1, O=16] a) 80.1 b) 48.1 c) 64 Exercise
What is the Mole ratio of reactants in the given
equation? 2C + 6Cl C 2 C l6
a) 6 : 2 b) 2 : 6 c) 8 : 6 d) 6 : 8
A formula that describes the actual number of atoms in a molecule is:
Molecular Formula b.Empirical Formula
c. Chemical Formula, d. Both a & b
A formula that gives the simplest whole number ratio of atoms in a formula unit :
a. Molecular Formula b.Empirical Formula
c. Chemical Formula d. Both a & b
Empirical formula for glucose C 6 H 12 O 6 is: a. C 3 H 6 O 3 , b. CH 2 O , c. C 2 H 4 O 2 , d. C 6 H 12 O 6
Find out the mole ratio in oxygen & aluminum in the reactants . 4Al + 3O 2 2Al 2 O 3 : a. 3/4 b. 6/4 c. 4/6 d. 2/6 The sum of atomic masses of all atoms present in a molecule is called: a. Molecular mass b. Formula mass c. Both a & b d. None of the above
1.How many moles are in 25.0 g of each of the following compounds?