11th Class Chemistry Chapter 4 Liquids and Solids Short Question Answer

Chemistry short QA

11th Class Chemistry Chapter 4 Liquids and Solids Short Question Answer

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1.What are dipole-induced dipole force?
These are those forces which are present among a molecule having a dipole and that molecule in which dipole has been induced.This induced dipole is due to the polar molecule which dipole molecule which collides with that.
2.London dispersion forces are weaker than dipole-dipole forces.Why?
London forces are short range forces.Dipoles are created due to the disturbance of electronic cloud momentarily.These forces only operate when dipoles are there.The dipole-dipole forces continue operating due to presence of permanent dipole and forces are strong.
3.Why the melting and boiling points of halogens and noble gas increase down the group?
The atomic sizes increase from fluorine to iodine.Same is the case with noble gases.The number of shells increase portability increase and the tendency of overlapping of loosely held electrons in orbitals increase in both groups.This makes the melting and boiling points high down the group.

4.Why inter molecular forces are weaker than intramuscular forces?
Inter molecular forces are present between two different molecules of the same kind or different kinds.Valence electrons are not responsible for these forces that is why they are weak forces.Hydrogen bonding and dipole-dipole forces are such forces.Intramuscular forces are present within the same molecule due to sharing of electrons and overlapping of the orbitals.In H2O the forces making bonds are intramuscular forces.

5.Is it true that polar compounds are soluble in polar solvents?
Polar compounds have separation of positive and negative charges.If the solvent has also separation of positive and negative charges than the interaction takes place between the opposite poles.These interactions are responsible to mix them with each other.

6.Why dipole-dipole forces are much stronger than dipole-induced dipole forces?
In dipole-dipole forces the atoms have sufficient partial positive and partial negative charges to attract each other.In dipole-induced dipole forces one of the atoms and molecules in non-polar and dipoles has to be induced in that.This induced dipole is temporary and that is why the attraction between a dipole and the induced dipole is comparatively less strong.
7.What are London dispersion forces?
In London dispersion forces there are no polarities before the collisions.Due to collision the electronic clouds in outermost orbitals of atoms or molecules are dispersed.Temporary dipoles are created and these temporary dipoles are responsible for attractive forces.These forces are very weak.
8.What is polarizability?How its increase down the group in noble gases is responsible for increase in melting and boiling points?
The polarizability is the capability of an atom molecule or an ion to be distorted for its electronic cloud.From upper to the downward direction in a group the atomic sizes increase in noble gases.Their outermost electronic clouds are disturded due to collisions.Temporary dipoles are developed and forces of attractions are created hence melting and boiling points increase down the group.
9.Why the melting and boiling points of alkalies increase with increase in molar masses and are less than that of H2O?
Alkalies are saturated hydrocarbons.Greater the length of carbon chain greater the interaction of one molecule with the other.Higher alkalies are zig -zag in structure and they are called macro-molecules  as well.These features are responsible for the forces of interaction and cause the increase of M.P and B.P.of alkalies.H2O is a polar liquids but alkalies are non-polar.
10.In the hydrogen bonded structure of HF which is the stronger bond;the shorter coalescent bond or the longer hydrogen bond between different molecules?
The covenant bond between H and F is stronger because it is produced by the overlapping of orbitals and two electrons are shared to give a sigma bond.The bond which is shown by the dotted lines is the hydrogen bond due to electrostatic forces of attraction.So it is a weaker bond.
11.What is the origin of the inter-molecular forces in water?
Due to difference of electromagnetically between hydrogen and oxygen in water polarity is developed.This causes hydrogen bonding among oxygen and hydrogen atoms in water molecules.
12.Water is a liquid at room temperature but H2S is a gas.Give reason?
This is due to high electromagnetically of oxygen as compared to sulphur.Water has hydrogen bonding but H2S  does not have.Due to absence of  hydrogen bonding in H2S at room temperature it is a gas.
13.Lower alcohols are water soluble but corresponding alkalies are insoluble in water.Why?
Alcohols have- OH group which is a polar and makes hydrogen bonds with water.This hydrogen bonding develops solubility.Hydrocarbons are non-polar molecules.They do not have any functional grou.So no hydrogen bonding and hence no solubility in water.
14.Water and ethanol can mix easily in all proportions.Why?
Water and ethanol have both OH groups.So they can do the hydrogen bonding extensively.That is why they can mix with each other in all proportions
15.How do you justify that the structure of ice is just like that of diamond?
The oxygen of water molecule is sp3 hybridized just like the carbon of diamond.Oxygen of water molecules makes two covalent bonds and two hydrogen bonds.So the hydrogen bonded water molecule in ice is just like the carbon of a diamond.
16.Briefly consider some of the effects on our lives if water has only a very weak hydrogen bonding present among its molecules?
Due to the expected weak hydrogen bonding in water the freezing point of water would be less than 0ᵒC.This would have its own problem for human being.Moreover the density of ice would not have been less than liquid water.So the sea animals would have different patter of living.
17.How in a very cold water fish in garden ponds owe their lives to hydrogen bonding?
When water is frozen at 0ᵒC than it expands. The hydrogen bonding in the solid state of H2O adjust the molecules of water in such a way that empty spaces are left behind.In this way the density of water in the solid state becomes less.So ice  floats on water.
18.H-bonding is present i chloroform and acetone.Justify it?
Chloroform is a polar compound.Acetone is also a polar compound.When chloroform and acetone are mixed with each other then create the forces of attractions due to hydrogen bonding.
19.Give the reason for low boiling point of HF(19.5ᵒC)as compared to H2O(100ᵒC) although the hydrogen in HF is stronger than that of water.
In water each molecule can make 2 hydrogen bonds with two neighboring water molecules.In this way the links of H2o molecule are greater.In case of HF these is only one partial positive  hydrogen which can make only one H-bord with another fluorine atom.
20.How the cleaning action of soaps and detergents is partially due to the hydrogen bonding?
Soaps and detergents are the sodium salts of long chain carboxylic acids and benzene sulphonates.The COONA– + group of soaps and SO3N+a group of detergents have a negative charge on oxygen atom and create hydrogen bonding with water.The rest of the portion of the soaps and detergents remain outside water.In this way water can do the cleaning action and removes the dirt and greasy material from the fabric.
21.Ice floats on water.justify it?
Ice is solid water.Water expands when it is solidified.This expansion is due to empty  spaces which are left behind due etc the hydrogen bonding.The density of ice is close to 0.91 g cm-3 as compared to that of liquid water which is 1.00 g cm-3 at 4ᵒC.For this reason ice floats on water.
22.In a very cold winter fish in garden ponds owe their lives to hydrogen bonding?
The hydrogen bonding in the solid  state  of H2O adjust the molecules of water in such a way that empty spaces are left behind.So the density of water in the solid state being less floats on water.The liquid water  at 4 ᵒC underneath ice accommodates fish in winter.
23.Why the heat of vaporization of water is greater than that of CH4?
Water is a polar liquid and due to strong hydrogen bonding high energy is required to separate the molecules from each other at its boiling point.CH4 is a non-polar and has weak London dispersion forces.
24.How the rate of evaporation depends on the surface area?
Evaporation is a surface phenomenon.Greater the surface area greater the number of molecules present on the surface;greater the chances to leave the surface and greater the evaporating tendency.
25.Steam causes more severe burns than does the boiling water.Give reason?
No doubt the temperature of boiling water and steam are same but the heat content of steam is greater that of boiling water.Te latent heat of vaporization is responsible for severe burns.
26.What is cleavage plane?
Crystalline substances have definite planes along which the crystals can be broken.This is an-isotropic behavior of the crystals.This property is associated with crytalline substances.
27.Solid sodium is a good conductor of electricity but solid sodium chloride is not.Give reason?
Sodium is an alkaline metal and free electrons are available in the crystal lattice.These free electrons are responsible for the passage of electrical current.Free electrons are not available in the NaCI crystal.
28.Sodium is softer than copper but both are very good electrical conductors?
Sodium is an alkali metal.It has one electrons in the outermost orbital.Copper is a transition element having ten electrons in outermost 3d orbitals.So there are greater chances for overlapping of orbitals in copper and hardness is developed.Well the availability of electrons to the applied potential difference is almost equal.SO they are equally good electrical conductor.
29.How does the solid maintain a definite volume and shape?
Since the particles of solids are closely packed so there are no empty spaces in the solid structure.For this reason they have definite volume.The shape of the solid depends upon the fixed arrangement of the constituency particles which gives them a definite shape.
30.Amorphous solid like glass is also called super cooled liquid.Why?
Amorphous solids like glass have random structures and their particles are disarranged just like liquids.So the amorphous solids are no doubt hard and rigid but look like liquids.That is why glass is called a super cooled liquid.
31.Define polymorpism and metamorphism.Give one example of each?
When a compound exists in more than one crystalline shape then the phenomena is called polymorphic.AgNO3 has rhomboidal and orthographic crystals.Isomorphic is a phenomenon in which two different substances exist in the same crystalline form.NaNO3 and KNO3 both show rhomboidal crystals.The atomic ratio in NaNO3 and KNO3 is 1:1:3.
32.The transition temperature is given by elements having allotropic forms and by compounds showing polymorphism.justify?
The elements having two or more than two crystalline forms have allot-ropes.Polymorphism is a property of a compound having two or more than two crystalline forms.At transition temperature one crystalline form changes to other.So transition is for all those elements which show allot-ropy and those compounds which show polymorphism.
33.How is that some of crystalline solid substances show anisotropy?
The variation of a certain physical property in different direction is known as anisotropy.Some of the crystalline substances are anisotropic for certain properties.Like electrical conductivity thermal conductivity passage of light and cleavage
34.Why graphite is an-isotropic in electrical conductivity?
Graphite has hexagonal plats structure.Electrical current can pass parallel to the layers but not perpendicular to the layers.The reason is that mobile electrons are available parallel to the layers.
35.Cleavage of crystals is anisotropic behaviour?
Anisotropy is the property of a crystal to obey a certain property better in one direction than the other.Cleavage is the breakage of a crystal along definite planes.Since cleavage of the crystals can take place only in particular directions so it is an-isotropic behavior.
36.Symmetry is one of the properties of a crystalline solid.Justify it?
Symmetry is the repetition of faces and angles of a crystal.when rotated by 360ᵒ along its axis.There are many types of elements of symmetry i,e.Center of symmetry plane of symmetry axis of symmetry and inverse axis of symmetry.
37.Crystals have their own habits.Justify it?
The shape of a crystal which usually grows is called the habit of crystal.A crystal grown in various directions.The shape of the crystal remains the same if the conditions remain the same.
38.What are crystallographic elements?
The complete description of the unit cell is given by six parameters.These are three edge lengths i.e. a,b,c and three inter facial angles i.e.These are called crystallographic elements.
39.What is reason for low lattice energy of NaCI as compared to MgCI2?
The charge density of Mg+2 is much greater than Na+. The forces of attraction between Mg+2 and CI.The close packing of MgCI2 results in higher lattice energy.
40.Naphthalene can be purified by sublimation process.why?
NaCI is an ionic compound and gives Na+ and CI in aqueous solutions.There ions allow the electrical current to pass through it.Glucose is a covenant compound and is not ionized in water.It is not able to conduct in solutions state.
41.Solid and liquid sodium is a good conductor of electricity but NaCI is only in molten state.Give reasons?
In ionic crystals each ion is surrounded by oppositely charged ions.If the size of the central ion is greater then the number of opposite ions surrounding it is also greater.It increases coordination number of central ion.The structure depends upon the coordination number.
42.Why the ionic crystalline solids have high melting points?
In the ionic crystalline solids the strong electrostatic forces of attraction are present in the crystal structure.The positively charged ion is surrounded by many negatively charged ions and vice versa.So the ionic solids have tightly packed structures and have high melting points.
43.Ionic crystals don’t conduct electricity in the solid state.Why?
In ionic crystals ions are tightly packed in a three dimensional way.They don’t have translatory motion.So they don’t become responsible for carrying of current.
44.Why the ionic crystals are highly brittle?
In ionic crystals the boundaries of similarly charged ions touch each other in the crystal lattice.So when a crystal is broken under stress they become loosely held then similar ions repel each other.This repulsion causes brittleness.
45.Why the lattice energy of NaCI is greater than that of KCI which is greater than KBr?
Smaller the size of positive and negative ions better the packing.In case of NaCI and KCI the size of Na+ is smaller than k+.So the lattice energy of NaCI is 788 Kj mol-1 while that of KCI is 690 kj mol-1.The size of Br is greater than CI.The packing of KBr is less tight than KCI.So the lattice energy of KBr is-665 kj mol-1.
46.Diamond an allot-rope of graphite is hard and an electrical insulator.Why?
There is sp3-sp3 effective overlapping of the carbon atoms in diamond.Tetrahedral angles are produced around each carbon atom.The bond length of 1.54 is most suitable for effective packing.That is why diamond has a hard structure.These are no electrons so it is insulator.
47.Diamond and graphite which are allot-ropes are covalent solids.Graphite can be used as a lubricant but diamond cannot be?
The electrons of the sigma bond in diamond due t sp3– sp3 overlapping are tightly held and are not available for decimalization in diamond.In graphite weak bonds are produced with the bond length of 3.4. Aᵒ due to p-p head-on overlapping between the layers.These electrons of p-orbitals make weak bonds between adjacent layers which can be broken.The layers can easily slip past each other.
48.Why most of the molecular solids have low melting and boiling points?
In these solids the molecules are connected with each other through inter-molecular forces.These forces are much weaker than normal bonds.So the melting and boiling points of the molecular solids are very low.Ice and solid CO2 are molecular solids.
49.Molecular solids are soft and easily compressible.why?
The molecules in such crytals are present at the lattice points.There are van der waal’s forces among the molecules of such solids.There forces are weak.So there solids are soft and easily compressible.
50.Metals are good conductors of heat and electricity.The conduction of electrical current decreases with the increase of temperature.Why?
This is due to the availability of free electron.The particles at the lattice points have to and fro motions.With the increase of temperature the extensions and compression’s are enhanced.So the probability of electrons to more freely becomes less.

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