CHAPTER-05

CHEMISTRY SSC-I                        CHAPTER-05

physical states of matter

typical properties

  1. Diffusion: The movement of molecules from a higher concentration to a lower concentration is called diffusion.

Example: (i)spreading of smell of rotten eggs.

(ii)Spreading of smell of perfume from one corner to the other corner of room.

  1. Effusion: The escape of gas molecules through the hole one after the other without collision is called effusion.

e.g escape of gas through puncture in tube.

  1. Pressure: Force exerted by a gas on unit area of a container is called its pressure. All gases exert pressure. At any point a gas exerts an equal pressure in all directions.

At sea level at 0OC the atmospheric pressure is 760mm of Hg or 760 torr. This pressure is referred as one atmosphere.

So, 1atm = 760mm Hg = 760 torr

The SI unit of pressure is the pascal (Pa) which is very small unit, so that kilopascal (kPa) is used for atmospheric pressure under ordinary conditions. One pascal equals force of one Newton exerted on an area of one square meter.

1atm = 101.325kPa= 1.01325 x 105Pa.

  1. Compressibility

Gases are highly compressible. This is due to the presence of large empty spaces between the gas molecules. On applying pressure distances between the gas molecules decrease, therefore, its volume decreases.

  1. Mobility

Gas can flow and can be transported through pipes over long distances but it can also leak more rapidly out of small hole. This is due to tendency of a gas to expand and fill the entire available space.

  1. Density

Gases have relatively low densities under normal conditions. This is because the molecules are much farther apart in the gas. When a gas is cooled its density increases because its volume decreases. For example, density of oxygen at 20oC is 1.4g/dm3 and at 0OC is 1.5g/dm3.

Effect on the volume of a gas by a change in pressure and temperature

EFFECT OF PRESSURE: According to the kinetic molecular theory, gas molecules are in constant random motion. They move in straight line until they collide with another molecule or the walls of the container. The pressure a gas exerts in a container is due to the force exerted on the walls of the container. On increasing pressure on the gas, the distance between molecules decreases. So the volume of the gas decreases. On decreasing pressure empty spaces between molecules increases , that results in increasing the volume of gas.

EFFECT OF TEMPERATURE:The average kinetic energy of gas molecules is directly proportional to the Kelvin temperature. when pressure of the gas is kept constant and temperature is increased, the average kinetic energy of gas molecules increases. So, the molecules of the gas hit the wall of container more frequently and energetically. This increases internal pressure. As a result, volume of the gas increases to restore constant pressure.

Laws related to gases: A sample of a gas can be characterised by four variables:

  1. Pressure (P)
  2. Volume (V)
  3. Temperature (T)
  4. The number of moles of gas (n)

The relationship that expresses the influence of one variable on another with the two variable constant are called gas laws.

 Boyle’s Law

In 1662 Robert Boyle studied the relationship between the volume and pressure of a gas at constant temperature. He observed that volume of a given mass of a gas is inversely proportional to its pressure provided the temperature remains constant.

Mathematically, it can be written as:

Where ‘k’ is proportionality constant. The value of k is same for the same amount of a given gas.

If P1V1 = k Then P2V2 = k

where P1 = Initial Pressure P2 = Final Pressure

V1 = Initial Volume V2 = Final Volume

As both equations have same constant therefore, their variables are also equal to each other.

P1V1 = P2V2

 

NUMERICALS

  1. Ethene is used as anaesthetic gas. The pressure on 2.5dm3 of ethene changes from 1.05 to 2.10 atm. The volume of ethene becomes 1.25dm3 if the temperature remains constant. Explain this change using Boyle’s law.

Ans:

P1 x V1 before change = 1.05 x atm x 2.5 dm3

= 2.625 atm. dm3

P2 x V2 after change = 2.1 atm x 1.25 dm3

= 2.625 atm. dm3

P1V1 = P2V2

Thus the calculated result agrees with the pressure-volume relationship according to the Boyle’s Law.

 

 

P(atm) V(dm3)
0.350 0.707
0.551 0.450
0.762 0.325
0.951 0.261
1.210 0.205
  1. A student obtained following data in an experiment at 20o Explain pressure-volume relationship using this data and the Boyle’s Law.

ANS:

Sr. P(atm) V(dm3) K=PV
1 0.350 0.707
2 0.551 0.450
3 0.762 0.325
4 0.951 0.261
5 1.210 0.205

 

  1. Ammonia gas is used as refrigerant 0.474 atm. pressure is required to change 2000cm3 sample of ammonia initially at 1.0 atm. to 4.22dm3 at constant temperature. Show that this data satisfies Boyle’s law.

Solution:

Initial pressure of ammonia=P1=  1 atm

Initial volume of ammonia = V1= 2000 cm3 = 2 dm3

After change volume = V2= 4.22 dm3

After change pressure= P2-= 0.474atm

According to Boyles Law

                P1 x V1 = P2 x V2

                1  x   2   = 0.474 x 4.22

                2.00 atm.dm3 = 2.00 atm .dm3

               

CHARLES LAW:

The law states that the volume of given mass of a gas varies directly with absolute temperature at constant pressure. Since the ratio of remains constant at constant pressure.

Mathematically                    V T

V= constant x T

= constant

This relationship is known as the Charles’s Law.

temperature as stated by the Charles’s law.

  1. A chemist obtained data shown in table in an experiment at 1 atm.
Temp. (C) Vol.(cm3) Tem (K) V/T
25 117.5
30 119.4
35 121.3
40 123.2

Explain volume-temperature relationship using Charles’s law.

  1. A bacterial culture isolated from sewage produces 36.4 cm3 of methane (CH4) gas at 27oC and 760mm Hg. This gas occupies 33.124 cm3 at 0oC and same pressure. Explain volume-temperature relationship from this data.
  2. A perfect elastic balloon filled with helium gas has a volume of 1.25×103dm3 at 1.00atm and 25oC on ascending to a certain altitude where temperature is 15oC the volume of balloon becomes 1.208×103dm3. Show that this data satisfies the Charles’s law.

Liquid State

It is a state of matter in which the constituent particles are loosely bound by intermolecular forces. Liquid change their shape with a fixed volume.

Typical Properties of Liquids

Some typical properties of liquids are given below:

1)            Evaporation                           2)           Boiling Point

3)            Vapour Pressure                  4)            Surface Tension

5)            Freezing Point                      6)            Density etc.

7)            Viscosity                                 8)            Diffusion

9)            Mobility

 

Define and Explain Evaporation Experimentally.

 

Evaporation

It refers to the conversion of a liquid to a gas or vapour at all temperatures but less than the Boiling point of the liquid is called Evaporation or vaporization.

Experimental Verification

In evaporation, we have to examine the movement of molecules in liquid. The molecules of a liquid are not motionless. The molecules which have low kinetic Energy move slowly, while others with high K.E move faster. This is clearly observed in an open container of Ether or Acetone. The volume of the liquid gradually decreases and finally no more liquid is left behind. This is because of Evaporation. Thus this spontaneous change of liquid into its vapours is called Evaporation and it continues at all temperatures.

 

  1. Evaporation is a Cooling Process?
  2. Liquids Evaporate faster when heated?

 

  1. Evaporation Causes Cooling

Evaporation Causes Cooling reason is that when high energy molecules leave the liquid and low energy molecules are left behind, the temperature of the liquid falls and heat moves from surrounding to liquid as a result temperature of surrounding also decreases. Hence- Evaporation is a cooling process and lower the temperature process of liquid.

 

CHEM: 9th                                              CHAPTER-5

LEC # 03                 STATES OF MATTER

 

  1. ii) Liquids Evaporate faster

Higher the temperature, faster is the rate of evaporation and vice versa. This is because added heat increases the Kinetic Energy of the molecules. Hence liquids evaporate faster when heated.

 

Vapour Pressure

The pressure exerted by the vapours of a liquid in equilibrium with its liquid at a given temperature is called vapour Pressure.

 

Explanation

Let us consider a liquid enclosed in a container. Air is evacuated and the vessel is sealed. The liquid then starts evaporating and its molecules collide with each other. Some of the molecules are recaptured by the liquid phase. This process is called Condensation. When two opposing process proceed exactly the same rate then the system is said to be in a dynamic state of equilibrium and the number of molecules in the vapour phase exerts a definite pressure which is called the vapour pressure of the liquid as shown in the figures.

Boiling Point

DEF: The temperature at which vapour Pressure of a liquid becomes equal to the external or atmospheric Pressure i.e 760mm Hg or 101.325 KPa at sea level is called Boiling Point.

The B.Point of some of the liquids are given below

Liquid Water Chloroform Ether Acetone Ethanol Ethanoic acid
B. Point (C) 100 61 35 56 78 119
B.Point (K) 373 334 308 329 351 392

Graphical Explanation

When a liquid is heated in an open container, average K.E of the molecules, increases and atmosphere exerts pressure on the liquid surface. Therefore, the temperature of the liquid gradually increases. This heating process overcome the attractive forces and increases the V.P of the liquids. At a certain temp, the V.P of the liquid becomes equal to the external or atmospheric Pressure. At this stage, bubbles of vapours from throughout the liquid, rise to surface and escape into the air and liquid starts boiling. This is called B.P of the liquids. The Graph clearly shows the variation in vapour Pressures at 101.325 KPa of four liquids with Boiling Points.

 

 

Variation in vapour pressures with temperature of four liquids.

Effect of External Pressure on Boiling Point

Liquids boil when their vapour pressure is equal to the pressure exerted on the liquid by its surroundings. The normal boiling point of water is 100oC.

  • In the mountains the atmospheric pressure is less than 1 atm. so water boils below 100o
  • In a pressure cooker at 2atm, water does not boil until the temperature reaches 120o

REASON:                To understand why water boils at 70oC on the top of Mount Everest and 120oC in a pressure cooker, although the normal boiling point of water is 100oC.

  • When the pressure of atmosphere is 1atm or 101.325 kPa water boils at 100oC at sea level. This is because at this temperature vapour pressure of water is 1atm or 101.325 kPa.
  • At Mount Everest at about 8850m above sea level atmospheric pressure is only 34kPa. So water boils at this height above sea level, when its vapour pressure is 34kPa at 70o So water boils at 70oC.
  • Pressure cooker is equipped with a valve that controls the pressure inside the pot. This valve generally exerts a pressure of 2 atm. Therefore, the valve does not allow water vapours to escape until the pressure inside the pot reaches 2 atm. Because vapour pressure of water becomes 2atm when the temperature reaches 1200 So water boils at 120oC in a pressure cooker.
  1. The boiling point of water on the top of Mount Everest is 70oC, while at Murree 98o Explain this difference.

Ans:

  1. If you try to cook an egg in boiling water while camping at an elevation of 0.5km in the mountain, you will find that it takes longer than it does at home. Explain? why

A process called distillation is used to purify liquids. Distillation is the process in which a liquid is heated to vapourize it and the vapours are cooled to condense them back to the liquid in a different container.

Solid State

In Solid State atoms, molecules or ions are very closely packed having definite shape and volume. They are in compressible and do not flow but vibrate about their fixed positions as shown in the figure.

The typical properties of solids are:

  1. Melting point/melting
  2. Freezing Point/Freezing
  • Sublimation etc.

Melting and Freezing

During heating, the particles of a solid start vibrating with greater Kinetic Energy. This makes the molecules a little bit apart from each other. This process increases the volume of solids. On future heating a stage reaches when the particles leave their fixed positions and start moving in the form of a liquid state as shown in the figure. This is called melting.

The temperature at which a solid turns into a liquid is called melting point.

On cooling, the liquid freezes. Thus freezing of a liquid is the reverse of melting. So the temperature at which a liquid changes into the solid is called Freezing Point.

Themelting and freezing of substances occurs at the same temperature. At this

temperature, the liquid and solid substances are in equilibrium each other.

Solid                                                       liquid

The Melting Point of a solid depends on the strength of attractive forces that hold particles together in the fixed positions. Stronger the forces higher will be the melting point. Ionic solids comparatively having high M.P than covalent solids.

CEMISTRY:9Th                                       chapter -05

STATES OF MATTER                             LEC# 04

 

Sublimation

The vaporization of a solid substance into the vapour phase without passing through the liquid phase is called sublimation.

Example:

Iodine, Benzoic Acid, Ammonium, Chloride naphthalene etc.

Explanation

When impure sample of Iodine molecule is heated on sand bath. After some time dark violet black crystals of Iodine deposit the underside of the glass water placed on the top of a beaker containing Solid Iodine. The iodine vapour Sublimates from Iodine crystals in the bottom of the beaker and Condenses to form crystals on the glass.

Types of Solids

On the basis of structure the solids have been divided into two classes based on their macroscopic appearance.

  1. a) Amorphous Solids
  2. b) Crystalline Solids
  3. Amorphous Solids

Amorphous is derived from Greek and “Amorphos” which means without shape. Hence Amorphous Solids are those in which atoms, ions or molecules are not arranged in a definite pattern, e.g. glass, Plastics, rubber etc..

Amorphous solids do not melt at a definite temperature but gradually soften when heated.

  1. Crystalline Solids

The solids in which atoms, molecules or ions are arranged in a regular repeating three- dimensional well- ordered pattern are called as crystalline solids. Crystals have regular shape. Particles forming the crystals are packed in a very exact and ordered pattern as shown in figure below.

 

Allotropy

The phenomenon of the existence of an element in different forms which have different physical properties but same chemical properties is known as ALLOTROPY and different forms will be called ALLOTROPES or ALLOTROPIC FORMS.

Allotropes of Carbon

Carbon has many Allotropic forms which are divided into two classes.

  1. Crystalline Allotropic forms: Diamond Graphite and Bucky Ball
  2. Non-crystalline Allotropic forms e.g: coal, coke, charcoal,Lamp black etc

 

Crystalline Allotropes of Carbon

Carbon has three crystalline allotropes. The arrangements and properties are given below:

  1. Diamond

It is the hardest known Substance in diamond; each carbon atom is covalently bonded to four other C-atoms which are arranged in the form of tetrahedron. Diamond is used for cutting glass and polishing hard surface because of rigid compact array .

 

Graphite

In Graphite, Carbon atoms are arranged in layers of hexagonal arrays. In these layers, each C-atoms is joined covalently by weak each Vender Waal’s forces. These layers slip over each other and makes Graphite Soft. Graphite is used as electrodes, lubricant in machines, and black pigment.

  1. Bucky Ball

It is new allotropic form which consists of forty to hundred carbon atoms. These atoms are arranged in a hollow cage like structure. Simplest molecule of Bucky Ball is made up of sixty C-atoms. Carbon atoms are arranged in Pentagons (Five member ring) and Hexagons (six member ring) just like a soccer Balls shown in the structure with the formula C60.

 

Allotropes of Phosphorus

Phosphours can exist in at least six different solid allotropic forms, three are common i.e white, Red and black phosphorus Phosphorus is a non-metal but here two are given.

  1. White Phosphorus

It is a very reactive, poisonous, volatile, waxy allotrope which is soluble in benzene and carbon disulphide. It exist in the form of tetra atomic molecules (P4) and form a tetrahedral structure as shown below:

  1. Red Phosphorus

It is much less reactive and poisonous than white Phosphorus. The tetra atomic molecules of red Phosphorus combine to form macromolecules in long chains.

 

Allotropes of Sulphur

Sulphur consists of molecules that contain eight atoms, S8covalently bonded with each other. Sulphur exist two crystalline allotropes i,e. Rhombic and monoclinic sulphurs while one non crystalline (Amorphous) Sulphuri,e Plastic sulphur.

 

 

 

 

CEMISTRY:9Th                                       chapter -05

STATES OF MATTER                             LEC# 05

 

Compare the three Physical States of Matter.

 Or Distinction between the three states of matter on the basis of particle model

SOLID LIQUID GAS
Has a definite shape and volume Has indefinite shape but definite volume Has indefinite shape and volume
Particles are  closely packed together bt have strong intermolecular forces Particles are not closely packed together bt have strong intermolecular forces Particles are free to move and have negligible  intermolecular forces
Particles can vibrate only along their mean position but cannot move. Particles move about freely and randomly in all directions with in surface of liquid Particles move about freely and randomly in all directions

 

SOCIETY, TECHNOLOGY AND SCIENCE

  1. Scientists use the power of reasoning to explain their observation. For instance when a balloon is filled with air, it expands. A scientist would explain it by saying that air molecules are free to move inside their container. There is no attractive or repulsive force between the molecules. As a result gas expands until it takes the shape of its container. Therefore, air expands to fill the interior of the balloon evenly.
  2. In early 1600s, Galileo argued that suction pumps were able to draw water from a well because of the force of vacuum” inside the pump. In 1946 Torricelli invented a device called barometer. He measured atmospheric pressure is 760mm Hg..
  3. Freeze-dried foods are light-weight and conveniently re-constituted by adding water. When salt is applied on meat it draws out considerable amount of water from the meat. After this meat is frozen and placed in a chamber attached to a vacuum pump. By lowering the pressure below the vapour pressure of ice, the ice crystals sublimate and the meat is dried without the loss of its flavour. Dried meat needs no refrigerator because bacteria such as salmonella which cause food poisoning cannot grow on salt and in the absence of moisture. Thus curing with the salt helps preserve meat.

EXERCISE

SHORT ANSWERS

 

  • Explain why volume of a gas decreases on increasing pressure on it at constant temperature?

Answer  According to Boyles Law volume and pressure are inversely proportional to each other at constant temp. High pressure on gas molecules increases the intermolecular forces as a result of which volume of gas molecules decreases.

  • How does temperature effect vapour pressure of a liquid? [SEE LEC # 3]
  • Water boils at 120°C in a pressure cooker, why?

Answer

Pressure Cooker is a closed container in which on heating B.P of water increases which help to increase the external pressure. A liquid can be made to boil at any temperature by changing the external pressure. So water boils at 120°C in a pressure Cooker because inside the pressure Cooker, external pressure increases.

  • Is evaporation a cooling process?

Answer

Yes. evaporation is a cooling process. [SEE LEC# 3]

  • Can you make water boil at 70°C?

Answer

Yes. A liquid can be made to boil at any temperature by changing the external pressure. Lower the external pressure, lower, will be the boiling point of water. Water boils at 1000C with 532 mm Hg Pressure.

  • Express the pressure 400mm Hg in kPa?

Answer

760mmHg is  = 101.325 Kpa

1mmHg is =  101.325/760

 

400 mm Hg of pressure = = 53.33 KPa

 Hence 400 mmHg = 53.33Kpa

Q.7:        Differentiate between amorphous and crystalline solidsQ12. The air in a perfectly elastic balloon occupies 855cm3, during the fall when the temperature is 20°C. During the winter, the temperature on a .particular day is -10°C, the balloon occupies 794.39cm3. If the pressure remains constant. Show that the given data proves the volume temperature relation according to the Charles Law.

Answer

V1 = 885cm3

T1= 20°C + 273 = 293K

V2 = 794.39cm3

T2 =-10°C + 273 = 263K

According to Charles Law =            =

 

=

3.02 cm3K -1= 3.02 cm3K -1

Hence it proves Charles law

 

Q13. In the past, gas volume was used as a way to measure temperature using devices called gas thermometers. An experimenter obtains following data from gas thermometer.

Volume (dm3) Temperature (°C)
2.7 0°C
3.7 100°C
5.7 300°C

Solution

According to Charles Law =            =  =

 

V1= 2.7dm3                           T1 = 0°C + 273 = 273 K

V2 = 3.7dm3                           T2= 100°C + 273 =373K

V3 = 5.7dm3                           T3 = 300°C + 273 = 573K

by putting the values

 

= =

 

0.00989 dm3 K-1 = 0.00992dm3 K-1 = 0.00994 dm3 K-1

9.89 cm3 K-1 = 9.92cm3 K-1= 9.94 cm3 K-1

 

Q.14 In automobile engine the gaseous fuel-air mixture enters the cylinder and is compressed by a moving piston before it is ignited. If the initial cylinder volume is 990cm3. After the piston moves up the volume is 90cm3. The fuel- air mixture initially has a pressure of 1. 0 atm and final pressure 11.0 atm. Do you think this change occurs according to the Boyles law.

Answer

V1 = 990cm3                         V2 = 90cm3

P1 = 1 .0atm                         P2 = 11 .0 atm

According to Boyles Law

P1 V1           =             P2V2

Putting the values

  • atm x 990cm3 =11.0 atm x 90cm3

990atm cm3 = 990 atm.cm3

Q15. A sample of neon that is used in a neon sign has a volume of 1500cm3 at a pressure of 636 torr. The volume of the gas after it is pumped into the glass tube of the sign is 1213.74cm3 when it shows a pressure of 786 torr. Show that this data obeys Boyle’s law?

Answer

V1= 1500cm3                                        P1= 636 torr

V2 = 1213.74cm3                                                   P2= 786 torr

According to Boyel’s Law

P1V1                                    =                              P2V2

636 torr x 1500cm3 =          786 torr x 1213.74 cm3

954000 torr cm3 = 954000 torr cm3

Q16. Instrumentation changes as science progresses, comment on it?

Answer

The search of man for collecting knowledge and integrating it is called Science. So true knowledge and its integration can be progressed more with the help of instruments. Some examples will prove the truth.

  • Exact heat changes during chemical reaction can be measured with the help of digital thermometer.
  • pH of solution, urine and blood can be measured exactly by pH-meter not by pH papers
  • Stethoscope uses doctor to listen heart beats and breathing
  • Barometer used for measuring air pressure easily
  • Mass spectrometer used to find out the atomic mass of an atom
  • Geologist easily detect the presence of oil and gas under earth with the help of instruments.
  • Micro organism easily seem by micro scope for better analysis
  • 1st date moon easily seen by powerful telescope
  • In medicine, use of instruments plays a vital role in the micro analysis of blood, urine, cancer, breaking bones etc. In short, Instrumentation changes as science progresses.

ELT ASSESSMENT EXERCISE 5.2

  1. At Mount Everest, the atmospheric pressure is 34 KPa which is about 8850 m above the sea level. While at Murree atmospheric pressure is 99.298 KPa which is comparative near to sea level. So at high altitude, the atoms pressure decreases, obviously B.P of water also decreases. Hence B.P of water at Mount Everest is 70°C while at Murree98°C.
  2. An egg in boiling water cooked longer while camping at an elevation of 0.5 Km in the mountain because at high altitude as compare 10*sea level, external pressure decreases which will decrease the Boiling point of the water. So it will take longer time than it does at home.

 

SELF ASSESSMENT EXERCISE 5.3

Give reason:

  1. When you put nail polish remover on you palm, you feel a sensation of coldness.
  2. Wet clothes dry quickly in summer than in winter.

Ans. 1

Nail Polish remover contains an organic solvent “Acetone”. It contains weak intermolecular forces and having high V.P. These high energy molecules escape from your palm and one feels sense of cooling. The other reason is that heat of body is used up to evaporate nail polish remover.

Ans.2

Greater the temperature of surrounding, greater the K.E possessed by the molecules and greater the escaping tendency from the surface of the liquids and Vice Versa. In summer, surrounding temperature is higher as compared to winter. So, wet clothes dry quickly in summer than in winter.

SELF ASSESSMENT EXERCISE 5.6

Sodium chloride, an ionic compound, has a high melting point of 801°C. Whereas molecular solid such as ice has relatively low melting point of 0°C. Explain this difference.

Ans.

In Sodium chloride, an ionic crystalline solid has strong electrostatic forces of attraction are present between positively charged ions with many negatively charged ions and Vice Versa while in molecular solids i.e ice, weaker intermolecular forces are present. So M.P of sodium chloride (801°C) is higher than molecular solids (0°C) that is ice.

 

 

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