Liquid state of matter

Liquid State

Ø  Intermediate state between solid and gas

Ø  Neither completely disordered nor completely ordered

Ø  The constituent particles of a liquid are in a state of continuous motion but at a slower speed than the gas molecules.

Ø  Fluids like gases; diffuse likes gases but at slower rates.

1.       Which is incorrect?

a.       A liquid has a definite freezing point.

b.       A liquid has a definite size.

c.        A liquid has a definite surface tension.

d.       A liquid has molecules held by hydrogen bonding.

Evaporation

Spontaneous changing of liquid into vapour at any temperature

Ø  Surface phenomena

Ø  A fraction of molecules having kinetic energy high enough escape the liquid from the surface.

Ø  Endothermic process - causes cooling

Heat – average kinetic energy of constituent particles of a body

Reason for cooling by evaporation: During evaporation particles with high kinetic energy escape into the vapour state and particles with lower kinetic energy are left in the liquid.

e.g. a drop of ether at room temperature on hand feels cold

-sweating occurs during summer to cause cooling by evaporation

Factor affecting evaporation

·         Nature of liquid (intermolecular force of attraction): Greater the intermolecular force of attraction lower the evaporation

·         Temperature: Higher the temperature higher the evaporation rate

·         Surface area: Higher the surface area higher the evaporation

·         Presence of impurities: The presence of nonvolatile impurities decreases the rate of evaporation.

2.       Evaporation of water is

a.       A process in which no heat change occurs.

b.       A process accompanied by a chemical reaction.

c.        Exothermic change

d.       Endothermic change

1.       Cooling is caused by evaporation. Give reason.                        2

2.       Mention two suitable examples to show evaporation causes cooling. 2

3.       Give reason: evaporation takes place from the surface of the liquid.   1

4.       State the physical principle behind the following phenomenon: A drop of ether on your skin disappears fast and the skin feels cool.                                                                               2

Condensation

- Conversion of vapour into liquid generally on cooling

- Condensation of water vapour in the atmosphere leads to rainfall resulting completion of the water cycle.

Vapour pressure

Ø  The pressure exerted by the vapour of liquid when the rate of evaporation is equal to the rate of condensation at a given temperature in a closed vessel.

Ø  Vapour pressure of water at a given temperature is also called aqueous tension.

Factors affecting vapour pressure

Ø  Nature of liquid

Ø  Temperature (directly proportional)

Ø  Presence of impurities

Non-volatile impurities decrease the vapour pressure of a liquid. Non-volatile particles on the surface reduce evaporation at a given temperature.

5.       Define the term aqueous tension.                                                    1

6.       Define aqueous tension. Why is it subtracted from the total pressure to determine the pressure of a dry gas?   2

7.       What is the effect of temperature on the vapour pressure of a liquid? 1

8.       What happens to the vapour pressure of the liquid if nonvolatile solute particles are dissolved in it?

 

Boiling point

Ø  The temperature at which a liquid boils at a given atmospheric pressure (generally 1 atm pressure)

Ø  A liquid boils when its vapour pressure equals the atmospheric pressure.

Ø  Bulk phenomena

Ø  Temperature remains constant throughout the boiling process. Because the heat supplied during the boiling process is used up by the molecules to change into a vapour state. Or the heat energy is taken by the vapouring molecules (particles) and the temperature liquid body remains constant.

Factors affecting the boiling point

Ø  Nature of liquid

Ø  Atmospheric pressure

 

3.       Boiling point of a liquid depends on all of the following except

a.       Viscosity                                                 c. External pressure

b.       Volume of the liquid taken                                d. Vapour pressure

4.       Which of the following does not affect boiling point?

a.       intermolecular forces                         c. external pressure

b.       nature of liquid                                    d. the initial temperature of the liquid

5.       Vapour pressure of a liquid increases with

a.       increase in intermolecular forces                    c. increase in pressure

b.       increase in polarity of molecules                      d. increase of temperature

9.       What do you mean by boiling point?                                              1

10.   In terms of vapour pressure what do you mean by boiling point?     1

11.   At what condition does a liquid boil?                                              1

12.   Point out the effect of increasing atmospheric pressure on the boiling point of a liquid.           1

13.   Why does the boiling point of a liquid rise with increasing pressure? 1

14.   Does atmospheric pressure affect the boiling point of a liquid? Explain.

15.   Boiling point of a liquid rises with increasing atmospheric pressure. Give reason.      2

16.   Boiling points of liquids P and Q are 70⁰C and 90⁰C respectively. Which of the two has a higher vapour pressure at 71⁰C? Give reason. 2

17.   Explain why the boiling point of water is lower at a higher altitude? 2

18.   Does the temperature of boiling liquid increase, decrease or remain constant even though the heat is continued? Give reason.                                                                                          1

Comparison of Evaporation and boiling

Boiling and evaporation are somewhat similar processes but they differ in many respects. The main differences may be outlined as

Evaporation	Boiling
1.       Evaporation takes place spontaneously in all temperatures.	1.       Boiling takes place only at a definite temperature called boiling point at which the vapour pressure of the liquid is equal to atmospheric pressure.
2.       Evaporation is a surface phenomenon, takes place only at the surface of the liquid.	2.      Boiling is a bulk phenomenon, takes place at the surface as well as below the surface.
3.       Generally evaporation is a silent process.	3.       Generally boiling is a noisy process.

19.   Differentiate between evaporation and boiling.                                2

20.   Write the differences between evaporation and boiling.

 

Surface tension

Force acting along the surface of a liquid at a right angle to any line of unit length. Unit: dyne cm^-1(SI system) or N m^-1(CGS system)_.

 

Factors affecting surface tension

Ø  Intermolecular force (nature of liquid)

Ø  Temperature

Effects/Applications of surface tension:

Ø  Falling water drops are spherical

Ø  Capillary action

Ø  Hot/warm food is tastier than cold

Ø  It’s easier to remove dirt from the clothes/dishes with hot water than cold

Ø  Soap/detergents act by increasing the surface tension of water

 

21.   Define surface tension. Write its unit.                                            2

22.   How is the surface tension of a liquid originated?                            2

23.   What is the effect of temperature on surface tension?                       1

24. Raindrops are spherical. Why?

25.   Give reason: falling liquid drops are spherical.                                2

26.   How does surface tension work to form the spherical shape of a liquid drop?

27.   Why is mercury droplet spherical?                                                 2

28.   Name the physical property behind the rise of liquids in a capillary tube.

29.   Write any two physical properties of liquids caused by surface tension.

30.   The meniscus for mercury in a glass tube is concave downward. Explain.

31.   The meniscus for mercury in a glass tube is concave downward. Why?

32.   It is more efficient to wash clothes in hot water than in cold water. Why?

Viscosity

Ø  Internal resistance to the flow of liquid.

Ø  Internal resistance or friction produced by one layer of liquid flowing over an adjacent layer with different velocities.

Ø  Coefficient of viscosity- the force per unit area required to maintain unit velocity gradient.

Ø  Unit of coefficient of viscosity: CGS- dynes s cm^-1 or poise; SI- Newton s m^-2 or Poiseulli

Factors affecting viscosity

Ø  Intermolecular force

Ø  Temperature

6.       Sugar solution is highly viscous due to

a.       Large molecular mass                                         c. Chain structure

b.       High intermolecular H- bond                             d. All of them

7.       When a liquid is heated

a.       Viscosity increases.                             c. Surface tension increases.

b.       Surface tension lowers.                      d. Surface tension is not affected.

33.   What do you understand by the term viscosity?                              2

34.   What do you mean by viscosity?

35.   Define the term coefficient of viscosity.

36.   What is the effect of temperature on viscosity?                                2

37.   Why glycerine is more viscous than water?                                    2

38.   Give reason alcohols can flow easily but honey cant.                        1

Liquid crystals and their applications

In general, liquids are isotropic and crystalline solids are characterized by anisotropic nature. There exist some liquids with properties somewhat in between the conventional liquid and crystalline solids. Such liquids are called liquid crystals. This is also considered the fourth state of matter. In general liquid crystals can flow like a liquid but their constituent particles are arranged in a crystal-like regular structure.

Liquid crystals have many important applications.

·         Their main application is in the liquid crystal displays (LCD) screen of the television, computer monitor, laptops, mobiles, watches, video games etc.

39.   Define liquid crystals and give their important applications.            2

 

8.       Which of the following statements is not true?

a.       A liquid is difficult to compress.

b.       Poise is a unit of surface tension.

c.        Evaporation causes the cooling of a liquid.

d.       Dyne cm^-1 is the unit of surface tension.

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

 

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. Cl₂ is 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 MgSO₄ is 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	SO42-	bisulphate	HSO4-
sulphite	SO32-	bisulphite	HSO3-
sulphide	S2-	hydroxide	OH-
carbonate	CO32-	bicarbonate	HCO3-
nitrate	NO3-	nitrite	NO2-
phosphate	PO43-	cyanide	CN-
fluoride	F-	chloride	Cl-
bromide	Br-	iodide	I-
chromate	CrO42-	peroxide	O2-
dichromate	Cr2O72-	permanganate	MnO4-
hydride	H-	thiosulphate	S2O32-
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)₃                                         g. NaAlO₂                   k. Hg₂O

d.      SO₃                                                            h_. (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 CH₂ and 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⁺²                          d. [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)₂              d.  Ca₃N₂

20.   The molecular formula of silver chromate is

a.       AgCrO₄                 b. Ag₂CrO₄                c. Ag₂CrO₆            d. Ag₂CrO₇

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

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

b.       AgCl₂, Fe₂CO₃, CuNO₃                                c. 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

2. Cu                                           ii. 63.4
3. Zn                                           iii. 65.5
4. 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. ***