Fundamentals of Chemistry

Q:- Define corpuscular theory of matter.

Ans. Corpuscular theory tells us that matter (universe) is made up of small particles (things). Two Greek philosophers named Empedocles and Democratus presented this theory in 5th century B.C.

Q:- What was the concept of Greek philosophers (Empedocles, Plato and Aristotle) about corpuscular theory of matter? Explain.

Ans. Ancient Greek philosophers presented different concepts about corpuscular theory as follows.

i. Empedocles theory.
A Greek philosopher, named Empedocles, was the first to say that all matter is made of four things, called earth, air, water and fire.

ii. Plato theory.
Plato followed Empedocles theory and called these four things elements.

iii. Aristotle theory.
Aristotle was another Greek philosopher (student of Plato) who adopted the same concept of four elements. But he added that these four elements are made of other four opposite elements called hot-cold and dry-wet. These four elements combine in pairs to form air, fire, water and earth.
For example, fire is formed from hot and dry, air is formed from hot and wet, water is formed from cold and wet and earth is formed from wet and dry. This concept of Greeks remained applicable for more than 2000 years.

Q:- Define chemistry.

Ans. It is the branch of science which deals with the study (examination) of matter and changes in matter.

Q:- Define different branches of chemistry.

Ans. The following are different branches of chemistry.

1. Analytical chemistry: It is that branch of chemistry which deals with the study of methods and instruments used for determination of composition of matter.
2. Biochemistry: It is that branch which deals with the study of chemical and physical changes taking place inside living things.
3. Environmental chemistry: It deals with the studies of harmful effects of chemicals on environment and human beings.
4. Inorganic chemistry: It deals with the study of elements and compounds other than organic compounds.
5. Industrial chemistry: It deals with the studies of methods and technology used for the large scale preparation of products in industries.
6. Nuclear chemistry: It deals with the changes in nuclei of atoms in various substances. [nuclei is plural of nucleus].
7. Organic chemistry: It studies substances having carbon in them, except carbon-monoxide
8. (CO),carbon-dioxide (CO2),carbonates (CO2-3) and bicarbonates (HCO­1-3).
9. Physical chemistry: It studies laws and theories to understand structure and changes in matter.

Q:- Write down different statements against each branch of chemistry to justify its definition.

Ans. The different statements against each branch of chemistry are as under;

1. Analytical Chemistry.
   • Elemental analysis shows that ammonia contains nitrogen and hydrogen elements.
   • Acetic acid is composed of carbon, hydrogen and carbon elements only.
   • Gasoline fumes are burnt in automobile engine to give energy.
   • Calorimeter is a device used to measure the amount heat a substance absorbs on heating or emits on cooling.
   • Sulphuric acid is weaker acid than hydrochloric acid.
   • Melting point of sodium chloride is 801^oC measured by Fisher-Johns Apparatus.
   • A chemist did an experiment to determine percentage purity of a sample of glucose.
2. Biochemistry.
   • Acetic acid causes so many chemical reactions inside human body.
   • Photosynthesis is a natural process used for production of food inside plants in presence of sunlight and chlorophyll.
   • Hair and nails contain keratins (proteins).
   • A cornstalk grows from a seed.
   • Some examples of complete protein food are meat, milk and eggs.
3. Environmental Chemistry.
   • Nitrogen dioxide (NO2) is responsible for acid rain.
   • Excessive drink of acetic acid causes adverse/harmful effects on human health.
   • Vehicles exhaust gases pollute the air or atmosphere.
   • Sulphur dioxide is the major source of acid rain.
   • Chlorofluorocarbons are responsible for ozone depletion.
   • Plantation helps in overcoming green house effect.
   • Light chlorinated hydrocarbons in drinking water are carcinogens (cancer causing).
4. Inorganic Chemistry.
   • Ammonia is soluble in water. It has no colour and has pungent irritating smell.
   • The study of carbon, oxygen and hydrogen elements in acetic acid (CH3COOH).
   • A silver article tarnishes in air.
5. Industrial Chemistry.
   • Haber’s process is used for large scale production of ammonia.
   • Acetic acid is prepared by oxidation of ethyl alcohol.
   • White lead is a pigment used by artists for centuries which is extracted from its ore, galena (PbS).
   • In Pakistan, most industries use wet process for cement production.
6. Nuclear Chemistry.
   • Bombardment of alpha rays or neutrons on compounds brings about nuclear changes.
   • The element radium is converted into radon by emitting α-particles.
   • Carbon-14 is continuously produced in the atmosphere when high energy neutrons from space collide with nitrogen-14.
7. Organic Chemistry.
   • Acetic acid is compound of carbon and is prepared from organic compound called ethyl alcohol (C2H5OH).
   • Acetylene is hydrocarbon composed of carbon and hydrogen elements.
   • Dynamite (C3H5N3O9) explodes to form a mixture of gases.
8. Physical Chemistry.
   • The change of solid to gas, gas to liquid or liquid to solid or solid to liquid etc.
   • Gases can be compressed by applying pressure.
   • Purple iodine vapours appear when solid iodine is warmed.
   • Ice floats on water.

Q:- How Archimedes (Greek philosopher) explained the purity of gold of the crown of a Greek emperor of his times?

Ans. Archimedes was a Greek philosopher and mathematician. The Greek emperor gave him a task to check the purity of his crown made of gold. One day Archimedes was taking bath and he observed that as he went deep in water, more volume (weight) of water was overflowed from bath tank.

He put a piece of gold in water in a pot. It displaced some water from there. He thought that the purity of gold could be determined from the amount (volume) of liquid water it displaced (overflowed) from the pot.
He meant that the quantity of water displaced by gold is equal to the weight of the gold piece dipped in it. He knew that if the crown was pure, then the amount of water displaced by it from a pot must be equal to the water displaced by equal weight of pure gold in another pot filled with same quantity of water.
He was very much excited by this thinking and ran from there shouting “Eureka” which means
“I found it”.

Q:- What is Dalton’s Atomic Theory? Write it postulates.

Ans. In 1803, a British scientist John Dalton presented his famous theory which has the following postulates.

• All elements are made of small indivisible particles called atoms.
• All atoms of an element are identical. They have same masses.
• During chemical reactions, atoms combine, separate or rearrange in simple ratios.
• Atoms can neither be created nor destroyed.

Q:- What are the defects of Dalton’s atomic theory? OR Which postulates of Dalton’s atomic theory were changed?

Ans. In 1850s, sub atomic particles (electrons, protons and neutrons) were discovered so the postulate that “atom is indivisible” was rejected. With the discovery of isotopes, the postulate that “all atoms of an elements are identical” was rejected. The two postulates of Dalton’s theory are still applicable.

Q:- Define atom. Give example.

Ans. The smallest particle of an element that cannot exist in free state is called atom. It is electrically neutral which means that it has no net charge because it has equal number of electrons and protons. For example, Na is an atom of sodium element, H is an atom of hydrogen element, Cl is an atom of chlorine element and C is an atom of carbon element.