Chemistry: Foundations & Fundamentals of Chemistry

1. Foundation and Fundamentals

General Introduction to Chemistry

Chemistry is the scientific study of matter.

Chemistry can be defined as the branch of science that deals with the study of composition, properties and transformation of matter.

The matter is anything that occupies space and has mass.

Scientific method

Universality

Predictability

Objectivity

Verifiability

Importance and Scope of Chemistry

Chemistry is very essential in modern day-to-day life as well as a part of the curriculum for basics in many of the modern fields of professions like medicine, pharmacy, biochemistry, anatomy, engineering, food and diary, nutrition, industries like beverages, paints, dyes, drugs, fertilizers, pesticides and so many.

It is involved in all parts of our life directly or indirectly. Fulfilment of basic needs also takes help from chemistry.

Food Shelter

Cloth Health

Education
Security

The Relationships between Some of the Major Branches of Science.

Chemistry lies more or less in the middle, which emphasizes its importance to many branches of science

1. Chemistry is a branch of science that deals with the composition and properties of matter. 1+2+3+2

a. Define matter.

b. Classify matter on a chemical basis.

c. Write four importance of chemistry.

d. Write four professional fields where chemistry finds its scope.

Basic Concepts of Chemistry

Atoms

An atom is the smallest and fundamental unit of an element, which possesses the properties of that element. E.g.: phosphorus, carbon and sodium.

Or,

Atoms can be defined as the smallest unit of the element that takes part in a chemical reaction.

Generally, atoms don’t exist in Free State in nature, except the atoms of noble gases.

Molecule

A molecule is the smallest particle of an element or compound, which has independent existence. E.g.: CO₂ is a molecule of compound Carbon dioxide. Cl₂is a molecule of the element chlorine.

It possesses all the properties of the element or compound.

Homoatomic molecule: molecules containing the atoms of the same element

Monoatomic molecules: He, Ne, Ar, Kr, Xe, Rd

Diatomic molecules: H₂, O₂, N₂, Cl₂ etc.

Triatomic molecule: O₃

Tetraatomic molecule: P₄

Octaatomic molecule: S₈

Heteroatomic molecule: molecule formed by the combination of two or more atoms of different elements. Eg. Water molecules (H₂O), carbon dioxide molecules (CO₂), sulphuric acid molecules (H₂SO₄) etc.

Ions/Radicals

An atom or a group of atoms having charge, which act as a single unit during a chemical reaction, are called radicals. The ions having positive charge are called cations and the ions having negative charge are known as anions. The cations of salt are called basic radicals and anions of salt are called acidic radicals. E.g., H⁺, O^--, Cl^-, SO₄^--, NH₄⁺ etc.

Valency

The combining capacity of an atom of an element or ion is called valency. For example: the valency of sodium in sodium chloride is 1; the valency of Mg in MgSO₄is 2; the valency of carbonate (CO₃^-2) is 2.

Chemical formula

The symbolic representation of a molecule of a substance is called the chemical formula. E.g.: H₂O is the formula for water, NaCl is for sodium chloride.

Molecular formula

The symbolic formula that shows the actual number of atoms of the elements in a molecule is called the molecular formula. For example: H₂O is the molecular formula of water, H₂S is the molecular formula of hydrogen sulphide gas.

Variable valency

Fe → + 2 (ferrous) & + 3 (ferric) Sn → + 2(stannous) & + 4(stannic)

Cu → + 1 & + 2 Hg → + 1 & + 2

Pb → + 2 & + 4

List of radicals/ions

Radicals	Formula	Radicals	Formula
sulphate	SO₄^2-	bisulphate	HSO₄^-
sulphite	SO₃^2-	bisulphite	HSO₃^-
sulphide	S^2-	hydroxide	OH^-
carbonate	CO₃^2-	bicarbonate	HCO₃^-
nitrate	NO₃^-	nitrite	NO₂^-
phosphate	PO₄^3-	cyanide	CN^-
fluoride	F^-	chloride	Cl^-
bromide	Br^-	iodide	I^-
chromate	CrO₄^2-	peroxide	O₂^-
dichromate	Cr₂O₇^2-	permanganate	MnO₄^-
hydride	H^-	thiosulphate	S₂O₃^2-
hypochlorite	ClO^-	chlorate	ClO₃^-
perchlorate	ClO₄^-	ferricyanide	[Fe(CN)₆]^3-
ammonium	NH₄⁺	ferrocyanide	[Fe(CN)₆]^4-

1. Write the chemical formula for the following compounds. 1 each

Barium sulphide Calcium hydride Ammonium hydroxide

Calcium sulphate Potassium sulphate Calcium cyanide

Silver nitrate Sodium nitrate Magnesium nitrate

Calcium bisulphite Sodium sulphite Magnesium bisulphate

Mercuric nitrite Sodium chlorate Lithium nitrite

Ferrous sulphate Ferric sulphate Potassium permanganate

Ammonium sulphate Ammonium nitrate Barium dichromate

Aluminium permanganate Sodium ferrocyanide

Potassium dichromate Sodium dichromate

Potassium thiosulphate Mercurous carbonate

Calcium chlorate Hydrogen chlorate

Cupric carbonate Ammonium carbonate

2. What are the valencies of underlined atoms/ions in the given compounds?

a. TiO₂ e. MnO₂ i. MnCO₃

b. Na₂ZnO₂ f. CH₃COONa j. (HCOO)₂Ca

c. Cr₂(SO₄)₃g.NaAlO₂ k. Hg₂O

d. SO₃h_.(NH₄)₂SO₄ l. Ca₂[Fe(CN)₆]

3. Washing soda has the molecular formula Na₂CO₃.10H₂O.

a. How many molecules of water are present in the formula?

b. Write the name of positive and negative radicals present in the formula.

c. What are the valencies of carbonate and sodium?

d. Define radicals and classify them with examples. 1+1+1+2

Relative Atomic Mass (atomic wt, atomic mass)

Atoms being extremely small it’s nearly impossible to measure the mass of individual atoms. Hence, the lightest element, hydrogen, was taken as the reference to express the masses of other elements. Therefore, the atomic mass of an element may be defined as,

Atomic mass of an element=

In this scale of atomic mass, there are a few problems like the isotope of hydrogen is not specified.

Later, the C-12 isotope was taken as standard by IUPAC. In this C-12 scale,

“The atomic mass of an element is a number which indicates how many times one atom of the element is heavier than one-twelfth of an atom of C¹² isotope.”

Mathematically,

Atomic mass of an element =

This atomic mass is not actual mass but relative atomic mass sometimes called atomic weight. Since the atomic mass is the ratio of two masses it should have no unit, but the atomic mass unit (amu) is considered the unit of atomic mass. Dalton ‘D’ is also the same as amu.

4. Define the atomic mass of an element. 2

Relative Molecular mass (weight)

Molecular mass is also defined similarly as atomic mass.

The relative atomic mass of a compound or an element is the number of times by which a molecule of the element is heavier than 1/12^th of a C-12 isotope.

Mathematically,

Molecular mass =

The molecular mass of a substance is calculated by summing up the mass of all the atoms present in the molecular formula.

Concept of Fractional Atomic Mass (weight)

In nature, most of the elements exist in the form of different isotopes. So the atomic mass of an element is naturally taken as an average of different isotopes of the element found in nature. This is the reason; the atomic masses of most elements are fractional.

5. Define isotopes giving an example. 2

6. Chlorine is naturally made up of 75% Cl-35 isotope and 25% Cl-37 isotope. Calculate the atomic mass of the chlorine element. 1

Solution: The average atomic mass of Cl = = 35.5 amu

7. Explain why atomic masses of elements are not whole numbers but are fractional? 1

Empirical formula

The symbolic formula which shows the simplest whole-number ratio of the number of atoms present in a molecule is called the empirical formula. The empirical formula of Ethene (C₂H₄) is CH₂and the empirical formula of water (H₂O) is H₂O.

More examples are shown in the table below.

Compound	Molecular formula	Empirical formula
Hydrogen peroxide	H₂O₂	HO
Benzene	C₆H₆	CH
Ethane	C₂H₆	CH₃
Glucose	C₆H₁₂O₆	CH₂O
Carbon dioxide	CO₂	CO₂
Butane	C₄H₁₀	C₂H₅

Percentage composition from molecular formula weight, atomic weight and valency

# Calculate the % composition of Na₂CO₃.10H₂O.

Molecular wt. = 23 x 2+12+16x 13 +1 x 20 = 286 amu (D)

% of Na = = 16.08%

% of C =

% of O =

% of H =

8. Limestone has the molecular formula CaCO₃,a basic raw material used to manufacture cement.

a. Define the term molecular formula.

b. Calculate the relative molecular mass of CaCO₃?

c. What are the acidic and basic radicals in the CaCO₃?

d. Calculate the percentage mass composition of CaCO₃. 1+1+1+2

MCQs

1. Which of the following is not a pure substance?

a. Diamond b. 24 carat gold c. Air d. Ammonia

2. The smallest particle of an element which retains all the properties and takes part in the chemical reactions is

a. molecule b. atom c. electron d. compound

3. Atomic number of calcium is

a. 40 b. 20 c. 35.5 d. 39

4. Which of the following sequence is correct if given elements are arranged according to ascending atomic number

a. Fe, Co, Ni, Cu

b. Co, Fe, Ni, Cu

c. Fe, Ni, Co, Cu

d. Cu, Fe, Co, Ni

5. Valency of an element depends upon

a. Total number of elements of an atom

b. Number of electrons present in the valance shell

c. Net positive charge present in the nucleus

d. All of the above

6. Variable valency is generally shown by

a. Representative elements

b. Transitional elements

c. P-block elements

d. Non-metals

7. Which of the following element does not show variable valency

a. Ag b. Cu c. Zn d. Fe

8. Which statement is erroneous?

a. Sodium is a monovalent element.

b. The atomic number of sodium is 11.

c. Methane is an organic compound.

d. Calcium shows variable valency.

9. The valency of Iron in ferric oxide (Fe₂O₃) is

a. 1 b. 1.5 c. 2 d. 3

10. Sulphate ion is

a. A compound c. An element

b. A divalent radical d. A trivalent radical

11. Cl^- is

a. electropositive ion c. basic radical

b. cation d. acid radical

12. The symbol of meta-aluminate is

a. AlO₂ b. AlO₂^- c. AlO₃^- d. AlO₃

13. The formula of sulphite, sulphide and sulphate are respectively?

a. SO₄^2-, S^2- and SO₃^2-

b. S^-, SO₂^-2 and SO₄⁺²

c. SO₃, SO₂ and SO₄

d. SO₃^-2, S^-2 and SO₄^-2

14. The formula of nitrite, sulphite, nitrate and sulphate ions are respectively?

a. N^-3, SO₄^-2, NO^-2 and SO₃^-2

b. NO₃^-, SO₃^-2, NO₂^-2 and SO₄^-2

c. NO₃^-2, SO₃^-2, NO₃^-2 and SO₄^-2

d. NO₂^-, SO₃^-2, NO₃^- and SO₄^-2

15. Which one of the following is a complex radical

a. CO₃^-2 b. Fe⁺³ c. Hg₂⁺²d. [Fe(CN)₆]^-3

16. The peroxide radical is

a. O₂^--b. O^-- c. O^- d. O

17. What is the number of electrons in ₁₂²⁴Mg²⁺?

a. 12 b. 24 c. 2 d. 10

18. The symbolic representation of a molecule of an element or a compound is called

a. Empirical formula c. Molecular formula

b. Structural formula d. Geometrical formula

19. The molecular formula of Calcium nitrite is

a. Ca₃NO₂ b. Ca(NO₂)₂ c. Ca(NO₃)₂d. Ca₃N₂

20. The molecular formula of silver chromate is

a. AgCrO₄ b. Ag₂CrO₄c.Ag₂CrO₆ d. Ag₂CrO₇

21. The molecular formula of silver chloride, ferrous carbonate and cupric nitrate are respectively

a. AgCl, FeCO₃ and Cu(NO₃)₂d. AgCl, Fe₂(CO₃)₃, Cu(NO₃)₂

b. AgCl₂, Fe₂CO₃, CuNO₃c. AgCl₂, FeCO₂, Cu₂NO₃

22. The molecular formula of sodium bicarbonate, sodium carbonate, magnesium nitrite and magnesium nitrate are respectively

a. NaHCO₃, Na₂CO₃, Mg(NO₂)₂, Mg(NO₃)₂

b. NaCO₃, Na₂HCO₃, Mg(NO₂)₂, Mg(NO₃)₂

c. NaHCO₃, NaCO₃, MgNO₂, Mg(NO₃)₂

d. NaHCO₃, Na₂CO₃, Mg(NO₂)₃, Mg(NO₃)₂

23. The formula which represents the exact number of atoms in a molecule is

a. condensed formula c. empirical formula

b. spatial formula d. molecular formula

24. What is the valency of mercury in Hg₂Cl₂?

a. 1 b. 2 c. 1/2 d. 2/3

25. An element M has an atomic mass of 19 and atomic number 9, its ion is represented by

a. M⁺ b. M⁺² c. M^- d. M^-2

26. An element X has an atomic mass of 39 and atomic number 19, its ion is represented by

a. X⁺ b. X⁺² c. X^- d. X^-2

27. A and B atoms have 2 and 6 valance electrons in their outermost orbit respectively, the compound that A and B are most likely to form is

a. AB₂ b. A₂B c. AB d. A₃B

28. How many electrons, protons and neutrons are present in the element represented by the symbol ₂₁X⁴³?

a. 22, 21, 21 b. 21, 21, 22 c. 22, 22, 22 d. 22, 21, 22

29. Relative atomic mass is

a. Number of protons

b. Number of protons + number of electrons

c. Number of times by which an atom is heavier than an atom of oxygen.

d. Number of times by which an atom is heavier than 1/12^th of the C¹² isotope.

30. According to IUPAC, atomic mass is expressed in terms of

a. H-1 b. C-12 c. O-16 d. Cl-35

31. What makes the atomic mass fractional?

a. number of unpaired electrons c. presence of isotopes

b. wave nature of electrons d. presence of isomers

32. Atomic number of calcium is

a. 40 b. 20 c. 35.5 d. 39

33. Relative atomic mass of chlorine is

a. 35 b. 36 c. 37 d. 35.5

34. The relative atomic mass of C in Na₂CO₃ is

a. 6 b. 12 c. 24 d. 16

35. What is the correct match of the elements and their atomic weights?

A. Ar i. 40

Cu ii. 63.4
Zn iii. 65.5
K iv. 39

(a) A-i, B-ii, C-iv, D-iii (c) D-i, C-iii, B-ii, A-iv

(b) A-i, B-ii, C-iii, D-iv (d) A-iv, B-iii, C-ii, D-i

36. The empirical formula of hydrogen peroxide is

a. H₂O₂ b. HO c. H₂O d. HO₂

37. The empirical formula of glucose (C₆H₁₂O₆) is

a. C₆H₁₂O₆ b. C₃H₆O₃ c. CH₂O d. CHO

38. Percentage of hydrogen is maximum in

a. CH₄ b. C₂H₄ c. C₆H₆ d. C₂H₆

*** This is not a complete note. It is just to guide you. It is recommended to study prescribed textbooks along with this material. ***

Labels: Chemistry class 11 NEB, chemistry notes, concise and comprehensive

Chemistry

Tuesday, February 7, 2023

Foundations & Fundamentals of Chemistry

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