Formula's of Molarity, Molality, Equivalent mass, no of gram equivalence and normality.

Formula's of Molarity, Molality, Equivalent mass, no of gram equivalence and normality.

Chemistry practical readings class 9th.

Experiment Readings: "Determine the melting point of the given compound: Naphthalene."

Chemistry Practical Readings: "determine the boiling point of organic liquids: acetone and benzene"

Experiment Readings: "Preperation of 250 cm3 and 500cm3 solutions of oxalic acid."

Chemistry Practical Readings: " standardize the given solution of sodium hydroxide by using oxalic acid solution"

Chemistry Practical Readings: "Standardize the given solution of hydrochloric acid by using sodium hydroxide solution."

How to draw neat and tidy diagrams?

Whether in your practical copies or your Exams, the drawings and diagrams have to be labelled and neat. If you add some shadings and sketchy marks to them, the merrier.
Here are some tips and tricks to make your work look neater:

1. Never ever draw the diagrams in the middle of the page, draw them towards the left, so that there is space for labeling's.
2. The diagram should not be very close to the top or bottom, but rather in the middle. There should however be space for the main heading, which should be below the drawing, not above it.
3. Give the main heading double underlines, and the labeling's single underlines, in case you have shortage of time or space (sometimes the labeling's are too many). 
4. Make the line end of the labeling's prominent by darkening the ends of the line.
5. Always use a full stop after each labeling.
6. make the first drawing with a light pencil, so that it can be rubbed off, when wrong. Once the first correct sketch has been drawn, only then use a dark pencil.
7. Use a tissue paper or cotton bud to shade or blend the shade.
8. Make sure your hands are clean before starting the labeling. Often shading leaves the hands gray because of the lead, so clean them up before starting the labeling.

Is any compound 100% ionic?

There is no compound which is 100% ionic. CsF should be most ionic but Francium is radio active.

CsF is not very ionic.

Ionic Compound, Covalent Compound and Coordinate Covalent Compounds.

Ionic Compound, Covalent compound and coordinate covalent bond.

Ionization Energy in Metals.

Question 7: 
 a:Explain why metals have low ionization energy?

STATEMENT: Metals have low ionization energy.

REASONING:

As we know that the atomic size of metals usually increases when we move from top to bottom in a group. As valence electrons are far apart from the nucleus so the force of attraction is smaller and less energy is required to remove the electrons from their outer most shell. That is why metals have low ionization energy.

In a period from left to right, metals have low ionization energy and the metallic character decreases.

B: Explain why metals have high second ionization energy as compared to the first one?

STATEMENT:

“Removal of second electron from an atom requires more energy than the removal of the first one.”

REASONING:

When an atom has to lose more than one electron, the energy required to remove the electron at first attempt is called the first ionization energy.

Mg  àMg+ +e- (7.64 eV)

The energy required to remove the second electron is called second ionization energy. This energy is always greater than the first ionization energy because after the removal of the first electron the nuclear charge increases and the positive nucleus pulls the remaining electrons closer.

Mg+ à Mg++ +e- (15.03 eV)

What are Inter-molecular forces?

What are the intermolecular forces? Explain in detail.

DEFINITION:

“The force of attraction present in the molecule of a compound is called intermolecular forces.”

CHARACTERISTICS OF INTERMOLECULAR FORCES:

1.       WEAK FORCES:

Usually these forces are very weaker than the bonding forces present with in these molecules.

2.       IN LIQUIDS AND GASES:

These forces are very weak among the molecules of gases and liquids.

3.       MELTING AND BOILING POINTS:

The melting and boiling points of liquids and solids depend upon the strength of these forces.

TYPES OF INTER MOLECULAR FORCES:

They are of three types:

·         Vander waal’s forces or London Dispersion Forces.

·         Dipole dipole forces.

·         Hydrogen Bonding

Law of Multiple Proportions.

LAW OF MULTIPLE PROPORTIONS:

This law was proposed by John Dalton (1763-1844) in the year 1803. He was not a good experimenter (perhaps because he was colorblind), but he skillfully used the results of others in formulating this law.

STATEMENT:

“When two elements combine together to form more than one compound, the different weight of one of these elements which combines with the definite weight of the other elemts are in simple ratio.”

EXAMPLES:

Compounds of “H” and “O”

S. No	Compound	Formula	Wt of O	Wt of H	Ratio
1	Water	H2O	16	2	2:16
2	Hydrogen peroxide	H2O2	32	2	2:32

Compounds of “C” and “O”

The oxygen-to-carbon mass ratio in carbon-di-oxide is twice that found in carbon monoxide.

S. No	Compound	Formula	Wt of C	Wt of O	Ratio
1	Carbon monoxide	CO	12	16	12:16
2	Carbon-di-oxide	CO2	12	32	12:32

Compounds of “N” and “O”

S. No	Compound	Formula	Wt of N	Wt of O	Ratio
1	Nitrous oxide	N2O	28	16	28:16
2	Nitric oxide	N2O2=NO	28	32	28:32
3	Nitrogen trioxide	N2O3	28	48	28:48
4	Nitrogen tetra oxide	N2O4=NO2	28	64	28:64
5	Nitrogen pent oxide	N2O5	28	80	28:80

CONCLUSION:

It is clear from all these examples that the law of multiple proportions is verified.

Importance of Chemistry and the harmful aspects of Chemistry.

Question.a. Explain the role of importance of chemistry.

b. How chemistry proves to be dangerous for us?

IMPORTANCE OF CHEMISTRY:

Chemistry plays an important role in our daily lives. It has not only changed our standard health conditions but infact almost every field of our lives.

1.       MAJOR GIGTS:

Synthetic fibers, nylon, plastics, medicines, soaps and detergents, cement, glass and fertilizers, cosmetics and explosives are the major gifts of chemistry.

2.       WELL BEING OF MANKIND:

Chemistry has contributed a lot to the well being of mankind in the form of food, clothing, shelter and medical treatment.

3.       AGRICULTURE:

Crops are being protected by using fertilizers, insecticides and pesticides.

4.       ARTIFICIAL PRODUCTS:

The production of a variety of artificial products has brought a revolution in our clothing. We wear colorful and fine dresses for all seasons.

5.       CONSTRUCTION OF BUILDINGS:

Cement, cast iron, pig iron, bricks, glass etc. are used in construction and a result from the knowledge of chemistry.

6.       PAINTS:

The attractive and colorful paints used for making our houses vibrant.

7.       Petroleum and petrochemicals provide countless facilities to us.

8.       Polyester fiber, fiber glass, multi color glasses, crockery, steel and alloys are the product of chemistry.

9.       NUCLEAR CHEMISTRY:

It provides us radio isotopes for the treatment of many diseases such as cancer. It also gives us atomic energy which can be used in various fields.

10.   ENVIRONMENTAL CHEMISTRY:

It gives us the knowledge about how to protect our environment from pollution.

DANGEROUS ASPECTS OF CHEMISTRY:

Although Chemistry has made our lives highly comfortable but it can be dangerous for us because:

11.   The smoke from Chemical industry and increasing number of automobiles cause air pollution which is responsible for damaging our environment. The polluted air has a very harmful effect on our health.

12.   The waste coming from chemical industries is full of dangerous chemicals and metals. It damages our lands, canals, rivers and most importantly our aquatic life.

13.   Excessive chemical sprays on our crops are affecting our daily lives.

14.   Chemical weapons and atom bombs have killed millions of people.

Law of Reciprocal Proportions: statement, example and conclusion.

Here is an example to tell how you will solve notes on the four chemical laws in Chapter 1.

Write a note on the Law of reciprocal proportions.

LAW OF RECIPROCAL PROPORTIONS:

This law was proposed by Ritcher in the year 1799. This law is also known as the “law of equivalent weights”.

STATEMENT:

“The weights of the elements which separately combine with the fixed weight of the third element are either the same or are the simple multiples of which they combine with each other.”

EXAMPLE:

Hydrogen combines with Oxygen to form water: H2O

2:16

1:8

Hydrogen combines with Carbon to form Methane: CH4

12:4

3:1

When carbon and oxygen combine with each other they for Carbon-di-oxide: CO2

12:16×2

12:32

3:8

CONCLUSION:

In both cases the mass ratio is the same 1.e 3:8. It proves the law of reciprocal proportion.

Q.6 Explain the following terms as used in chemistry: donor atom, acceptor atom, electron gas/ sea theory, electronegativity, ionization energy and octet rule.

1. DONOR ATOM: In an coordinate covalent bond the atom which supplies or donates an electron pair for sharing is called donor atom e.g. when an acid is added to water , it dissociates and gives a hydrogen ions. This reacts with H2O to form H3O+. In this case oxygen of water donates a lone pair of electron to H+ to form a coordinate covalent bond. The oxygen atom of H2O has two lone pairs of electron and acts as an electron pair donor.

2. ACCEPTOR ATOM: In a coordinate covalent bond the atom accepts an electron pair from the donor is called acceptor atom e.g. when an acid is added to water, it dissociates and gives hydrogen ion. The oxygen atom of h2o has two lone pairs of electrons. On the other hand, H+ ion has no electron and acts as an electron pair acceptor.

3. ELECTRON GAS OR ELECTRON SEA: Electron sea theory was o by Drade and Loven. According to this theory the valence electrons of a metal atom are not firmly held by the nucleus due to large size and low ionization potential of metal atoms. These electrons form a sea of electrons and can move easily from one atom to the other.

4. ELECTRONEGATIVITY: The power of an atom to attract a shared pair of electron in a covalent bond is called electro negativity e.g. the electro negativity of hydrogen is 2.1.

5. IONZATION ENERGY: Ionization energy means the the least energy required to expel electron from the outer most shell of a gaseous atom to convert it into a positive ion e.g. the ionization energy of sodium is 5.14eV.

6. OCTET RULE: When an atom has eight electrons in its outer most shell it is said to be stable and does not combine with other atoms to reduce its energy. This is called octet rule. All the noble gases except Helium follow the octet rule.

Compare exothermic and endothermic reaction?

• EXOTHERMIC REACTION:
• DEFINITION: ENERGY RELEASING REACTIONA ARE SAID TO BE EXOTHERMIC.
• EXPLANATION: We know that bond breaking always consumes energy and that bond making always releases energy. The balance between these two processes results in two types of reactions. When the energy released by bond forming is greater than energy consumed by bond breaking there is a net release of chemical energy by the reaction. In an exothermic reaction energy is transferred to the surroundings.
• EXAMPLES:
• The reactions of fuels with oxygen of the air are all highly exothermic and the energy released can be used as a heating source, cooking meal or to drive an engine.
• 2.       C(s)+O2(g)àCO2(g)   +∆H= -393.5 kj/mol
• 3.       H2(g)+O2 (g)à H2O  ∆H= -242 kj/mol                 
• CONCLUSION: In simple words, chemical reactions in which heat is evolved are called exothermic reactions.
• ENDOTHERMIC REACTIONS:
• DEFINITION: ENERGY ABSORBING REACTIONS ARE SAID TO BE ENDOTHERMIC.
• EXPLANATION: When the energy of bond breaking is greater than the energy of bond forming, the chemical reaction must be driven by the energy absorbed from the surroundings.
• EXAMPLES:
• 1.       Conversion of liquid water into its vapors is an endothermic process.
• 2.       H2O(l)àH2O2 (g) ∆H= +40.7 kj/mol

•       3.       H2+I2à2 HI(g)  ∆H=52.96 kj/mol
•       4.       N2 +O2à 2NO ∆H=180.6 kj/mol
• CONCLUSION: In other words, chemical reactions which are accompanied by the absorption of heat are called endothermic reactions.

Define pH. Derive the equation [H+]=[OH-]

DEFINITION: 

“The pH of a solution is defined as the negative of the logarithm of the hydrogen ion concentration”

MATHEMATICAL EXPRESSION:

 In mathematical terms: pH= -log[H+]

DERIVATION: 

The equation for the ionization of water is: H2OàH+ + OH-……….(eq 1)

The expression for the equilibrium constant for this reaction is:

K=[H+] [OH-] / [H2O] or K[H2O]= [H+][OH-]……..(eq 2)

Since dissociation of water into ions is very small, therefore the concentration of H2O remains constant. As, K[H2O]=Kw , So equation 2 can be written as Kw=[H+][OH-]……(eq3)

This new constant is called dissociation constant of water. The value of Kw of water at 25 degree is 1.0^-14.

Thus equation 3 can be written as: Kw= [H+][OH-]=1.0^-14 ………(eq4)

CONCLUSION: 

Since one H+ ion is produced for every OH- ion , therefore, the concentration of H+ ion will be equal to the concentration of OH- ions i-e [H+]=[OH-]. This fact help us to calculate the concentration of H+ or OH- ions, which comes out to be 1.0^-7 mol/L. Any solution in which [H+]={OH-] is known as neutral solution.

Q.5 Explain why: Why hydrogen molecule is more stable than hydrogen atom?, Why Helium exists in the form of He and not He2 ?, Why hydrogen chloride is a covalent compound but sodium chloride is an ionic compound?, Why is NaCl a bad conductor of an electricity in the solid crystalline form but a good conductor in the molten state?,In the formation of H2 molecule, why is the octet rule not obeyed?, Why metals are good conductors of electricity?

• Why hydrogen molecule is more stable than hydrogen atom?
• Every system in this universe tends to attain stability by lowering it's energy. similarly hydrogen also tends to gain stability. so two moles hydrogen atoms combine by releasing 435 KJ enegy to form one mole hydrogen molecule. This means that hydrogen molecule is more stable than hydrogen atoms as it has less energy than hydrogen atoms.
• Why Helium exists in the form of He and not He2 ? 
• Helium atom has only one shell i-e K-shell which can accommodate a maximum of two electrons which it already has. therefore Helium atom does not need any more electrons to become stable as it is already stable by duplet rule. Thus helium atom does not combine with another helium atom and hence exists as He and not He2.
• Why hydrogen chloride is a covalent compound but sodium chloride is an ionic compound?
• Covalent bonds are formed when the electronegativity difference between the two atoms is less than 1.7. Ionic bond is formed between two atoms having electronegativity difference of 1.7 or above. The electronegativity of hydrogen is 2.1 and that of chlorine is 3.0. So in HCl the electronegativity difference is 3.0-2.1=0.9 which is less than 1.7. Therefore they will form a covalent compound. Electronegativity of Sodium is 0.9 and that of chlorine is 3.0. So the electronegativity difference is 3.0-0.9=2.1 that is greater than 1.7 and will form an ionic bond and hence it will be an ionic bond.
• Why is NaCl a bad conductor of an electricity in the solid crystalline form but a good conductor in the molten state?
• In solid crystalline form the sodium ions and the chloride ions are firmly held together due to electrostatic forces of attraction and are unable to move. Therefore solid sodium chloride is a bad conductor of electricity. On the other hand in molten form the ions are free to move and become responsible for conducting electricity.
• In the formation of H2 molecule, why is the octet rule not obeyed?
• hydrogen atoms have only one shell( K-shell) which can accommodate only two electrons. Therefore each hydrogen atom in hydrogen molecule contributes one electron forming a pair which is shared between the two atoms. Thus in hydrogen molecule duplet rule is followed and not the octet rule.
•  Why metals are good conductors of electricity?
• According to electron sea theory the valence electrons of a metal atom are not firmly held by the nucleus due to large size and low ionization of metal atoms. These electrons form a sea of electrons and can move easily from one atom to the other. Therefore metals conduct heat are known as good conductors of electricity.