Fundamentals of Chemistry

Q:- How an atom can be seen and weighed?

Ans. Many scientists thought that an atom is a mental construction because it cannot be seen with naked eyes. However, with the advancement of science, scientist made scanning tunneling microscope which is used to visualize atoms. Mass spectrometer can be used to weigh atom.

Q:- Define matter. Name its three states.

Ans. Anything which occupies space and has weight is called matter. It has three states, i.e solid, liquid and gas.

Q:- Define substance. Give examples.

Ans. Any matter which has different characteristics from any other kind of matter around it is called substance. OR
Anything which is pure is called substance. For example, sodium (Na), water (H2O) and sodium chloride (NaCl) etc. It means all elements or compounds in pure form are called substances.

Q:- Define element. Give examples.

Ans. A substance which cannot be divided into simpler substances is called element. OR
A substance which has all its atoms with same atomic number is called element.
For example, sodium (Na), gold (Au), Silver (Ag) and potassium (K) etc. Elements have uniform composition.

Q:- Explain molecularity of physical world.

Ans. Molecularity of physical world means that this world is made up of molecules. Entire physical world is made of mixtures. Mixtures are made of elements and compounds which are made of molecules. So we can say that physical world is made of molecules and this property is called molecularity of physical world.
Elements are the building blocks of living and non-living things in this universe. The elements which make up this earth also make up the moon.
Air consists of polyatomic molecules, like O₂, N₂, CO₂ , H₂O and noble gases. Water consists of polyatomic molecules which covers 70% of earth crust and also fills the empty spaces under the earth. Clay and sand also consists of long chain molecules called giant molecules. Petroleum and coal are also composed of molecules. Living things are also formed of thousands of different substances which exist in the form of large molecules (polymers), like carbohydrates, proteins, fats, lipids, DNA and RNA etc. Simply, this world is made up of molecules

Q:- Highlight the importance of garlic.

Ans. Garlic produces bad breath which may be good for you. Garlic contains more than 200 compounds and has the following uses.

• It is used against stomach cancer.
• It may cure heart diseases.
• It may lower the chances of stroke.

Q:- Define compound. Give examples.

Ans. A compound is a substance which is formed of two or more than two elements combined in a fixed ratio by a natural force called chemical bond. For example water (H₂O), sulphuric acid (H₂SO₄), ammonia (NH₃), nitric acid (HNO₃) and sodium chloride (NaCl) etc.
Remember that both elements and compounds have uniform composition which means that both are formed of same type of particles.

Q:- What is a mixture. Give examples.

Ans. A mixture is formed by two or more than two different types of substances (elements or compounds) which retain their properties. For example, salt dissolved in water or iron pieces mixed with clay.

Q:- Explain the types of mixture. Give examples.

Ans. There are two types of mixture.

1. Homogeneous mixture. It is a mixture which has uniform (same) composition throughout its body. OR It is that mixture having one phase. For example, sugar or sodium chloride dissolved in water.
2. Heterogeneous mixture. It is that type of mixture which is formed of two or more than two visibly different components. OR It is a mixture which has more than one phases. For example, iron pieces added in water.

Q:- What are the differences between compounds and mixtures?

Ans. The following table shows the differences.