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Fundamental of Chemistry: Solved exercise and think tank

Question: Give short answers.

I. Differentiate between an ion and a free radical.

Answer.  

An ion is a charged specie formed from an atom or chemically bonded group of atoms. For example, 

Na+( sodium ion) , Mg2+ (magnesium ion) , CN- (cyanide ion) etc.

On other hand, a free radical  is an atom which has unpaired electron  or odd no of electrons and has no electrical charge. For example, 

H ( hydrogen free radical) 

Cl (chlorine free radical)

ii. What do you know about the corpuscular nature of matter.

Answer. 

Initially the corpuscular nature of matter was purposed by Luucippus and democritus. The corpuscular nature of matter means matter is made up of corpuscles (بہت چھوٹے ذرات)  or tiny individual particles named atoms. This concept was not accepted by Aristotle. However, in 17th century, the concept of corpuscular theory became popular again. In 19th century, John  Dalton again proposed that is matter is composed of corpuscules called atoms.


iii. Differentiate between analytical chemistry and Environmental Chemistry.

Analytical chemistry is the branch of chemistry that deals methods and instruments for determining the composition of matter. 

While environmental chemistry is the branch of chemistry that deals with the chemicals and toxic substance that pollute the environment and their adverse effects on human beings.

iv. What is mole?


v. Differentiate between empirical formula and molecular formula.

vi. What is the number of molecules present in 9.0 gram of Steam?

Answer 

Molecular mass of Steam (H2O) = 2×Atomic mass of H + Atomic mass of O

                                                               = 2× 1.008 + 16   = 18.016 amu

Molar mass of Steam   = 18.016 g

1 mole of Steam    = 18.016 g

OR

18.008 g of steam  = 1mole of steam

1 g of steam            = 1/18.016

9 g of steam           = (1/18.016) × 9  = 0.4995559503 moles

1 mole of Steam = 6.022 × 1023    molecules

4995559503 moles of steam = 0.4995559503 ×6.022 × 1023  molecules 

                                                    = 3.008 × 1023  molecules

Example: Formaldehyde is used to preserve dead animals. Its molecular formula is CH2O.  Calculate the number of moles that would contain 3.011 × 1022 molecules of this compound. 

Solution: 

6.022 × 1023 molecules of formaldehyde  = 1 mole of formaldehyde  

1 molecule of formaldehyde 

= 1/6.022 × 1023 moles of formaldehyde 

= 3.011 × 1022 molecule of formaldehyde 

= 3.011 x 1022  × 1 /6.022 × 1023    

  = 0.05 moles of formaldehyde  


vii.  What are the molar mass of Uranium 238 uranium 235?

    Answer.

Let 

Uranium 238

Atomic mass of Uranium-238 = 238 amu

molar mass of Uranium-238 = 238g

Let 

Uranium 238

Atomic mass of Uranium-235 = 235 amu

molar mass of Uranium-235 = 235 g

viii. Why one  mole hydrogen molecules and one mole of hydrogen atom have different masses?

Answer. 

This is because  a molecule of  hydrogen contains two hydrogen atoms so its molecular mass is 2 amu, Hence, its molar mass (1mole) is 2g. On the other hand, atomic mass of hydrogen atom  is 1 amu. Hence its molar mass (1mole) is 1g. For instance,

Molecular mass of hydrogen molecule (H2) = 2 amu

Molar mass of H2  = 2g

One mole of H2   = 2g 

Atomic mass of Hydrogen = 1 amu 

molar mass of hydrogen  atom = 1 g

one mole of  hydrogen atoms

Question 2. Define ion  molecular ion  formula unit   free radical, atomic number, mass number and  atomic mass unit.

Differentiate between an atom and Iron Man chlorine and free radical..

Question 4. Describe how Avogadro's number is related to a mole of any substan

Question: calculate the number of moles of each substance in samples without following masses.

a. 2.4 g of the He

b 250 mg of carbon

c. 15 g of solution chloride 

d. 40 g of sulphur 

e. 1.5 kg of MgO


Answer. 

a. 2.4 g of He

Molecular mass of He = 4 amu

Molar mas of He = 4g 

1 mole of He = 4g 

OR

4 g of He  = 1mole of He

1 g of He   = 1/4:mole of He

2.4 g of He =  (1/4) × 2.4 g of He = 0.6 mole

b. 250 mg of Carbon 

  25o mg of Carbon  =  0.25 g of  carbon 

Let 

Atomic mass of carbon = 12 amu

Molar mass of carbon   = 12 g

1 mole of carbon  = 12 g

OR 

12 g of carbon  = 1mole

1 g of carbon   = 1/12 mole 

0.25 g of carbon  = (1/12) ×0.25 g of carbon = 0.02083333

c. 15 g of solution chloride 

Formula mass of sodium chloride (NaCl) = 23 + 35.5 = 58.5 amu

Molar mass of NaCl  = 58.5 g

1 mole of NaCl = 58.5 g

OR

58.5 g of NaCl = 1 mole

1 g of carbon = (1/58.5) mole 

15 g of NaCl = (1/58.5) × 15g NaCl= 0.2564 moles

Question7: calculate the mass in grams of each of the following sample

a. 1.2 moles of K

b. 75 moles of H2

c. 0.25 moles of steam 

d. 1.09 moles of benzene C6H6.

d. 0.01 moles of acetic acid CH3COOH 

Answer 

Question 9: Decide whether or not each of following is an example of empirical formula.

a. Al2Cl3

b. Hg2Cl2

c. NaCl

d. C2H5O

Answer 

a. Empirical formula 

b. Not empirical formula 

c. Empirical formula 

d. Empirical formula 


Question 10: TNT Ultra toluene is an example of compound used in bomb it contains 7- C atoms,  5-H atoms, 3-N atom and 6- O atoms. write its Imperial formula.

Question 11. Molecule contains four Phosphorus atoms and 10 oxygen atom write the empirical formula of this compound also determine the molar mass of his molecule.

Question 12: indigo ( C16H10N2O2), the dye used to color blue jeans is drived from a compound noun has endoxide c8h7o n.

Calculate the molar masses of these compounds also write their empirical formula.

Question 13. Identify the substance that has formula mass of 133.5 AMU.

a. MgCl2

b. S2Cl2

c. BCl3

d. AlCl3

Question 14. Calculate the number of atoms in each of the following sample.

a. 3.4 moles of Nitrogen atoms

b. 23 g of Na

c. 5 g of H atoms.

Question 15: Calculate the masses of the following:

a. 3.24 × 1018 atoms if Iron

b. 2 × 1010 molecules of Nitrogen gas.

c. 1 × 1025 molecules of water 

d. 3 × 106 atoms of Al.

Question 16. Identify the branch of chemistry the deals with the following samples.

1. I can't talk gross from a seed 

2. Dynamite (C2H5N3O9) explodes to form a mixture of gases.

3. Purple iodine vapour appears when solid iodine is warmed.

4.Gasoline ( amixer of hydrocarbons) fumes are ignited in an automobile engine.

5. A silver article turns in air. 

6 Ice floats on waters.

7. Sulphur dioxide is a major source of acid rain. 

8. Many other light chloride nature hydrocarbon and drinking water or carcinogens.

9.  In Pakistan most of the factories use wet process for the production of cement.

10.  Carbon 14 is continuously produced in atmosphere when high energy 14.

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