Class 9th Chemistry Unit 5 Question And Answer
Class 9th Chemistry Unit 5 Question And Answer On Newsongoogle By Bilal Articles
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Unit 5
Q1: Define flatter.
Ans: For Everything which occupies some space and has mass is called matter Air, Wood, H2SO4 etc
Q2: Write down the names of different states of matter.
Ans: There are three states of matter i) Solid ii) Liquid iii) Gas
Q3: Describe gaseous state of matter.
Ans: Matter in gaseous state does not have definite shape and volume. Therefore, cases occupy all the available space. Gases have very weak intermolecular forces.
Q4: Define Diffusion. On what factor diffusion of gases depends?
Ans: Diffusion is spontaneous mixing up of molecules by random motion and collisions to form a homogeneous mixture. Factors: Rate of diffusion depends upon the molecular mass of the gas.
Q5: Define Effusion. On what factor it depends?
Ans: It is escaping of gas molecules through a tiny hole into a space with lesser pressure. Example: when a tyre gets punctured air effuses out. Factor: Effusion depends upon the molecular masses of gases.
Q6: Define Pressure. Writes down its Sl unit.
Ans: Pressure: The force (F) exerted per unit surface area (A) S.I unit of pressure: The SI unit of force is Newton and that of area is m². Hence pressure has Sl unit of Nm². It is also called Pascal (Pa):
Q7: Write down the name of instruments with the help of, we measure the pressure?
Ans: There are two instruments with the help of we measure the pressure: Barometer: Barometer is used to measure the atmosphere pressure ii) Manometer: It is used to measure the pressure in laboratory.
Q8: Define standard atmospheric pressure.
Ans: It is defined as the pressure exerted by mercury column of 760mm height of sea level. It is sufficient pressure to support a column of mercury in height at sea level.
Q9: How Cases are compressible?
Ans: Cases are highly compressible due to empty spaces een their molecules.
Q 10: Describe the mobility of gas molecules.
Ans: Gas molecules are always in state of continuous motion. They can move from one place to another because gas molecules possess very high kinetic energy. of continue
Q 11: Describe the density of gases.
Ans: Density is the ratio of mass and volume (m/v). Gases have low density than liquid and solids. Density of gases is expressed in grams per dm³
Q 12: Why the rate of diffusion of gases is rapid than that of liquid?
Ans: Because gas molecules have insignificant intermolecular forces as compared to liquid. So the rate of diffusion of gases is rapid than that of liquid.
Q 13: What do you mean by Pascal? How many Pascal are equal to 1-atm?
Ans: Pascal is the SI unit of pressure One Pascal=1 Nm-2
Q 14: Whether the density of a gas decrease on cooling.
Ans: The density of gases increases by cooling because their volume decreases. For example, at nominal atmospheric pressure the density of oxygen gas is 1.4 gdm³ at 20 deg * C mid 1.5 gdm³ at 0 deg * C
Q 15: Why is the density of gas measured in gmdm³, while that of a liquid is expressed in gcm³?
Ans: Gases have low densities due to light mass and more volume occupied by the gas molecules. That is why gas density is expressed in grams per d * m ^ 3 whereas liquid and solid densities are expressed in gram per c * m ^ 3 because liquids and solid are 1000 times denser than gases.
Q 17: Define Boyle’s law.
Ans: Volume of a given mass of a gas is inversely proportional to its pressure provided the temperature remains constant
Q18: Who was Robert Boyle?
Ans: Robert Boyle (1627-1691) was natural philosopher, chemist, physicist and inventor. He is famous for Boyle’s law of gases.
Q 19: Is the Boyle’s law applicable to liquids?
Ans: No, Boyle’s law only applicable on gas.
Q 20: Is the Boyle’s law valid at very high temperature?
Ans: No. it is only valid at constant temperature.
Q 21: What will happen if the pressure on a sample of gas is raised three times and its temperature is kept constant’?
Ans: If the pressure on a simple gas is raised three times s at constant temperature, the volume will also decrease three times of its original volume.
Q 22: Who was J. Charles?
Ans: J. Charles (1746-1823) was a French inventor, described in 1802, how gases tend to expand mathematician and balloonist. He heated.
Q 23: Define Charles law.
Ans: J. Charles in 1789 presented his law that “the volume of a given mass of a gas is directly proportional to the absolute temperature if the pressure is kept constant”.
Q 24: What is absolute temperature scale?
Ans: Lord Kelvin introduced absolute temperature scale or Kelvin scale. This scale of temperature starts from O-K (-273.15°C) which is given the name of absolute zero. It is the temperature at which an ideal gas would have zero volume.
Q 25: Which parameters are kept constant in Charles’s Law?
Ans: In Charles law pressure remains constant.
Q 26: Why volume of gas decreases with increase of pressure?
Ans: The volume of gas decreases with increase of pressure because pressure and volume both are inversely proportional to each other so when we increase pressure, volume will decrease and when volume increases, pressure decreases.
Q 27: Does Kelvin scale show a negative temperature?
Ans: The Kelvin scale does not show negative value as O-K = -273°C
Q 28: When a gas, is allowed to expand, what will be its effect on its temperature?
Ans: Temperature will be increased because volume and temperature is directly proportional to each other.
Q 29: Can you cool a gas by increasing its volume?
Ans: Yes, by sudden increasing the volume of a gas, it gives the cooling effect.
Q 30: In which units body temperature is measured?
Ans: Body temperature is measured in Fahrenheit and is equivalent to 37°C. This temperatu temperature. Normal body temperature is 98.6F. close to average normal atmospheric
Q 31: What is meant by liquid.
Ans: Matter that has indefinite shape but a definite volume is called liquid. For example, Water, milk etc.
Q 32: Define evaporation. On which factors it depends.
Ans: The Process of escaping molecules spontaneously mom the surface of a liquid is called evaporation. It depends upon following factors. 1.Temperature 2.Surface tension 3.intermolecular forces
Q 33: Explain evaporation causes cooling.
Ans: When the high kinetic energy molecules vaporize the temperature of remaining molecules falls down. To compensate this deficiency of energy, the molecules of liquid absorb energy from the surrounding. As a result, the temperature of surrounding decreases and we feel cooling.
Q 34: Define vapour pressure.
Ans: The pressure exerted by the vapour of a liquid at equilibrium with the liquid at a particular temperature is called vapour pressure of a liquid.
Q 35: Write down the names of factors on which vapour pressure depends.
Ans: There are following factors: i) Nature of liquid ii) Size of molecule iii) Temperature
Q 36: Define boiling point.
Ans: The temperature at which the vapour pressure on its surface is called boiling point. dis equal to atmospheric pressure
Q 37: Write down the names of factors which boiling point depends.
Ans: The factors on which boiling point depends are: Nature of liquid Intermuscular forces External pressure.
Q 38: Define freezing point.
Ans: Freezing point of a liquid is that temperature at which vapour pressure of liquid phase is equal to the vapour pressure of the solid phase. At this temperature liquid and solid coexist in dynamic equilibrium with one another.
Q 39: Define diffusion. In which factors diffusion of liquid depends?
Ans: “The spontaneous movement of molecules from the region tit higher concentration of the region of lower concentration is called diffusion” Factors: diffusion depends upon following factors. 1.intermolecular forces 2.Size of molecules 3.Shape of molecules
Q 40: Describe density of liquid.
Ans: The density of liquid depends upon its mass and volume. Liquid are denser than gases because molecules of liquids are closely packed anal spaces between their molecules all negligible. The density of liquid is expressed in the gram per cm³.
Q 41: Why does evaporation increase with increase in temperature?
Ans: the evaporation increases with increase in temperature because kinetic energy of the molecules increases with increase in temperature. This K.E is so high that they overcome the intermolecular forces and evaporation rapidly.
Q 42: What do you mean by condensation?
Ans: The process of moving the molecules from the is called condensation. pours phase back into the liquid phase
Q 43: Why the vapour pressure eis higher at high temperature?
Ans: At high temperature the vapour pressure is higher than aa low temperature. When temperature increases the kinetic energy of the molecules increases enough to enable them to vaporize and exerts pressure so the vapour pressure increases at high temperature
Q 44: Why the boiling point of water is higher than of alcohol?
Ans: The boiling Point of water is higher than of alcohol because water has stronger inter molecular forces.
Q 45: What do you mean by dynamic equilibrium?
Ans: When the rate of evaporation becomes equal to rate of condensation at stage, the number of molecules evaporating will be equal to the number of molecules coming back to liquid. This state is called dynamic equilibrium.
Q 46: Why arc the rate of diffusion in liquid slower than that of gas?
Ans: The rate of diffusion in liquid slower than that of gas because liquid has stronger intermolecular forces, as compared to gases so the rate of diffusion is slower than that of gases.
Q 47: Why does the rate of diffusion increase with increase in temperature?
Ans: Diffusion increases by increasing temperature because at high temperature the intermolecular forces are weak, so rate of diffusion increases.
Q 48: Why liquids are mobile.
Ans: The ease of flow of liquid is called mobility. Because the ease of flow of liquid depends upon the strength of intermolecular attractive forces, the weaker the strength of these forces, the more mobile is the liquid and vice versa. Due to this mobility of molecules, liquid can be poured from one vessel in another ves
Q 49: What is meant by solid?
Ans: Matter that has a definite shape and plastic etc. is called solid. for example, wood, coal,
Q 50: Define melting point.
Ans: The temperature at which a solid substance is converted into a liquid is called melting point of the solid substance.
Q 51: Explain the rigidity of solid.
Ans: The particles of solids are not mobile. They have fixed positions. Therefore, solids are rigid in their structure.
Q 52: Explain density of solid.
Ans: Solids are denser than liquids and gases because solid particles are closely packed and do not have empty space between their particles. So, they have high density as compare to liquid and gases.
Q 53: Define amorphous solids. Give example.
Ans: Amorphous solids means shapeless solid in which the particles are not regularly arranged or their regular shapes are destroyed.
Q 54: Define crystalline solids. Give example.
Ans: Solids in which particles are arranged in a definite three dimensions pattern are called crystalline solids. Example: Diamond, sodium chloride etc.
Q 55: Define allotropy and give any two examples.
Ans: The Phenomenon in which an element exists in different forms having different physical properties but same chemical properties is called allotropy. Examples: (i) Carbon has three allotropic forms e.g., Diamond, Graphite and Bucky balls. (ii) Sulphur has two allotropic forms e.g. Rhombic sulphur and Monoclinic sulphur.
Q 56: Define transition temperature.
Ans: The temperature at which one allotrope changes into another is called transition temperature.
Q 57: In which form of sulphur exists at room temperature?
Ans: Rhombic Sulphur exists on room temperature.
Q 58: Why is white tin available at room temperature?
Ans: The transition temperature of two allotropic forms of tin is 18°C. So, this temperature indicates white tin is more stable above 18°C.
Q 59: Why the melting point of a solid is considered its identification characteristics?
Ans: Because the solid particle possess only vibrational kinetic energy. When solids are heated their vibrational energies increases and particles vibrate at their mean position with a high speed.
Q 60: Which is lightest one, aluminum or gold?
Ans: Aluminum is lighter than gold because the density of aluminum is lesser than gold. For example, density of aluminum is 2.70 gcm³ and gold is 9.3 gcm³.
Q 61: Write the molecular formula of a sulphur molecule?
Ans: Formula of sulphur molecule is Sg.
Q 62: Which allotropic form of carbon is stable at room temperature (25°C)?
Ans: Diamond, graphite and Bucky balls are Stable forms of carbon at room temperature. Among these allotropic forms, graphite is energetically slightly more stable than diamond.
Q 63: State whether allotropy is shown by elements or compounds or both.
Ans: Allotropy is shown by only elements because the existence of tin element in more than one forms in same physical state, tan the other hand compound do not show this property her hand
Q 64: What is diffusion? Explain with an example.
Ans: The spontaneous movement of molecules from the region of higher concentration to the region of lower concentration is called diffusion. Example: For example, when a few drops of ink are added in a beaker of water, ink molecules move around and after a while spread in whole of the beaker.
Q 65: Define standard atmospheric pressure. What are its units? How it is related to Pascal?
Ans: It is the pressure exerted by the atmosphere at the sea level. It is the pressure exerted by a mercury column of 760mm height at sea level.
Q 66: What do you mean by evaporation? How it is affected by surface area? Ans: The press of a liquid into a gas phase is called evaporation. Evaporation is a surface phenomenon. Greater is the surface area greater is evaporation and vice versa.
Q 67: In which form sulphur exists at 100°C
Ans: Sulphur exists in monoclinic form at 100°C.
Q 68: What is the relationship between evaporation and boiling point of a liquid?
Ans: A figured having higher boiling point will have slow evaporation due to stronger inter interlecular forces. A liquid having low boiling point will have faster evaporation.
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