Chemistry
Explain why grignard reagents should be prepared under anhydrous conditions ?
These are prepared under anhydrous conditions as they easily react with water to give following reaction :-
Explain why alkyl halides , though polar , are immiscible with water?
The alkyl halides are polar in nature , but the molecules in them are strongly held by the hydrogen bonds formed between H and X (halide = F, Cl, Br atoms). these bonds are not easily broken, a lot of energy is required to break this interaction. Even the heat released at the time of
Explain why the dipole moment of chlorobenzene is lower than cyclohexyl chloride ?
There are two major aspects that can explain this :- The C-Cl bond in case of chlorobenzene is having some double bond like character , which is indicated by its shorter bond length. thus it indicates the back-flow of electrons from the Chlorine to the Carbon. Thus the polarity decreases and it shows non polar
what are ambident nucleophiles ?
The nucleophiles which can attack from more than one sides (sites) or which have more than one elecron rich sites are called ambident nucleophiles .
Why are pantahalides more covalent than trihalides?
It can be easily learned by Fazan’s rule that ion with more charge/radius ratio has more polarizing power. Now in case of pentahalides +5 , the charge/radius ratio is higher than +3, thus pentahalides have more polarizing power , thus it shows covalent character.
What is meant by elementary step in a reaction ?
There are certain reactions that complete in a series of small steps , each complementary step is called an elementary step . and such reaction is called a complex reaction.
How does the value of rate constant vary with reaction concentration ?
the rate constant is a constant term , whose value does not change with change in concentration . thus the value of k doesn’t change.
How the alkaline medium prevents the rusting of iron ?
The Rate of rusting of iron depends upon the availability of H+ ions , more the ions more will be the rusting. But if we provide the alkaline medium , it will decrease the concentration of H+ ions. Thus the iron will not be oxidized from Fe to Fe2+ .
Why Aluminium metal cannot be produced by the electrolysis of aqueous solution of aluminium salt ?
The discharge potential of Al3+ ion is higher than that of H+ , thus if we are using the aqueous solution of aluminium salt the hydronium ions are preferably discharged giving H2 gas at cathode and Al will remain in the solution. Thus we can not get Aluminium metal by electrolysis.
Why rusting of iron is more in saline water than that of normal water ?
Rusting of iron is an electrochemical process , the presence of any ion facilitates the formation of rust. In saline water the presence of Na+ and Cl– ions increase the conductivity of the top layer of the iron , forming the Fe2+ ions . Thus the formation of Fe2O3 X H2O takes place quickly.
Arrange the following metals in order in which they displace each other from the solutions of their salts. Al, Cu, Fe, Mg and Zn.
A metal with lower electrode potential can easily displace the metal with higher electrode potential from its salt solution . here are the metals arranged in their increasing order :- Mg , Al , Zn , Fe , Cu
What do you mean by standard hydrogen electrode (S.H.E) ?
Standard hydrogen electrode is the hydrogen electrode whose electrode potential is zero. half cell equation for this is as given below :- Pt , H2 1(atm) / H+ (1M) ; E0 = 0
Why do the aquatic animals feel more comfortable in winter than in summer ?
This is due to a simple fact that the gasses dissolve in cold water, as the temperature of water rises the dissolution rate of gases in water decreases. Animals need oxygen gas for respiration . which is easily available at the time of winter but during summer less gas is available for the respiration .
What are the uses of reverse osmosis ?
reverse osmosis is used in water filteration. in desalination of salty water in the purification of blood at the condition of kidney failure
When a mixture of liquids show positive deviation from ideal behaviour ?
This happens due to the fact that the intermolecular forces between the particles of mixture are lower than that of the pure liquids. In this case the attractions between the A-B particles are lower than that of A-A interactions and B-B interactions.
When a mixture of of liquids shows negative deviation from ideal behaviour?
This happens due to the fact that the intermolecular forces between the particles of mixture are higher than that of the pure liquids. In this case the attractions between the A-B particles are higher than that of A-A interactions and B-B interactions.
Osmotic pressure is a colligative property ?
It is a colligative property because the osmotic pressure is directly proportional to the number of solute particles.
Define term solution . How many types of solutions are formed ? write briefly about each type with an example.
the homogeneous solution of two substances is called a solution. Solute and solvent are the two parts of a solution . Solvent :- it is the component of the solution which is present in large amount. Solute :- it is the component of the solution which is present in small amount. Classification on the basis
what is meant by the term peptisation ?
It is the process of conversion of freshly prepared peresipitate into colloidal state by the addition of proper electrolyte.
What happenes when an electric field is applied to a colloidal dispersion ?
The colloidal particles are charged in nature, thus on the application of electric field, the particles move towards the opposite pole and get neutralise and finally accumulate on the electrodes . This whole process is known as Electrophoresis .
What is the formula of Dichloridobis(ethane-1,2-diamine) platinum (IV)nitrate ?
Here is the formula :- [PtCl₂(en)₂](NO3)2
What is the formula of Amminebromidochloridonitrito-N-platinate (II) ?
Here is the formula :- [Pt(NH3)Br CI(NO₂)] ion
What is the formula of Tris(ethane-1,2-diamine) chromium (III) chloride (iv) ?
Here is the formula :- [Cr(en)3] Cl,
What is chemical equilibrium ?
In case of reversible reactions , if the products are allowed to stand undisturbed then they start the backward reaction. This process happens until we get 1:1 of products and reactants. The whole phenomenon is called chemical equilibrium.
Why is molality preferred over the molarity ?
In case of molarity the volume of solvent is taken but in case of molality the mass of solvent is taken. With change in temprature the volume can increase or decrease but the mass remains same . So molality is preferred over the molarity. The main reason for this is that the molarity is the
Benzene is soluble in toluene but not in water . Why ?
Like dissolves like. Toluene is a non polar solvent and benzene is also non polar in nature, so it dissolves in toluene. But on the other hand water is a non polar solvent and due to this benzene do not dissolve in it.
what is the chemical symbol for gold ?
Au is the symbol used for gold metal. This symbol is taken from the Latin language and in Latin language gold is known as Aurum.
Why N2 (nitrogen molecule) is less reactive or show inert behavior ?
In case of Nitrogen molecule, the two atoms of Nitrogen are joined with each other by triple bond. And to break this bond we require large amount of energy. This makes the molecule nearly inert. As shown below.
Why halogens are coloured ?
In case of halogens the electrons present in outer shell absorb the energy in visible region and get excited to higher level . During these transitions the emissions are in visible region thus these compounds appear coloured.
what are emulsions ? write two examples of emulsification.
Emulsion is the type of colliodal mixture :- In which the dispersion medium is oil and dispersed phase is water. for example ‘Butter’ In which the dispersion medium is water and dispersed phase is oil. for example ‘milk’ . Applications or examples of emulsification In case of cleaning action of soap, the soap solution acts
What happens when an electric field is applied to a colloidal solution ? or what is electrophoresis ?
On the application of electric field , the colloidal particles move towards the oppositely charged electrode. on reaching at the electrode , the particles get discharged and they coagulate there. this process is also known as the Electrophoresis.
Give reason for why the enthalpy in case of chemisorption is usually higher than that of physisorption ?
In case of chemisorption there is a partial bond like interaction between the adsorbate and adsorbent . During such an interaction the higher amount of energy is required because bond formation and breaking will require more energy. but on the other hand in case of physisorption the adsorbate and adsorbent particles are simply held together
Give reason why the path of light becomes visible when it is passed through As2S3 solution in water ?
In case of As2S3 the colloidal particles scatter the light passing through solution and show Tyndall effect.
Give reason why enzyme catalysts are highly specific in their action.
In case of enzyme catalyst , they have specific sites for the attachment of substrate or the reactant. Any other molecule or substrate can not join with the catalyst. here is a diagram to show the phenomenon.
Give an example of each , differentiate between multimolecular and macromolecular colloids ?
Multimolecular colloids :- These kind of colloids are formed when many small molecules or atoms are forced to aggregate in the dispersion medium. Thses colliods are lyophobic (solvent hating) in nature. for example gold solution Macromolecular colloids :- These are colloids which are formed of such a molecules which are enough large to have colloidal
Why is freezing point depression of 0.1 M sodium chloride solution is nearly twice that of 0.1 M glucose solution ?
the depression in freezing point (which is a colligative property) depends upon the number of solute particles present in the solution. when sodium chloride is mixed in the water it dissociates into Na+ and Cl– ions thus this increases the number of particles . but glucose don’t dissociate and its freezing point is higher than
Of 0.1 molal solutions of glucose and sodium chloride respectively, which one will have a higher boiling point ?
The elevation in boiling point depends upon the number of solute particles present in the solution. when sodium chloride is mixed in the water it dissociates into Na+ and Cl– ions thus this increases the number of particles . but glucose don’t dissociate and its boiling point is lower than Sodium chloride.
A 0.1539 molal aqueous solution of cane sugar (molar mass = 342g ) has a freezing point of 271K while the freezing point of pure water is 273.15K . what will be the freezing point of an aqueous solution containing 5g of glucose (molar mass= 180g) per 100 g of solution?
Molality of the given solution = 0.1539m ∆Tf = 273.15 – 271 = 2.15 K Therefore ∆Tf = Kf .m Kf = ∆Tf / m Kf = 2.15/0.1539 Now mass of the solute W2 = 5g Molar mass of the solute M2 = 180g Mass of the solution W1 = 100g Now the mass of
An antifreeze solution is prepared from 222.6 g of ethylene glycol C2H4(OH)2 and 200g of water . Calculate the molality of the solution . If the density of the solution is 1.072 g per / ml -1 , then what shall be the molarity of the solution ?
Solution:- Mass of ethylene glycol (solute) = 222.6 g Molar mass of ethylene glycol ( C2H4(OH)2 = 62g Number of moles of the solute = 222.6 / 62 = 3.59 moles Mass of the solvent (water) in solution = 200g = 0.200Kg Volume of the solution = 422.6 / 1.072 = 394.2 ml =
Which of the 3-d series of the transition metals exhibit the largest number of oxidation states and why ?
In case of transition metals the Manganese exhibit large range of oxidation state from +2 to +7. This is due to the fact that it has the highest number of unpaired electrons in its outer shell. The configuration of Mn is [Ar] 3d5 4s2 thius it can use its 7 electrons to show the large
In the series Sc(Z=21) to Zn (Z= 30) the enthalpy of atomization of zinc is the lowest i.e. 126 Kj /mol. Why?
In case of zinc its outer d-subshell is fully filled. So it can not make interatomic bonds like the other elements of the same transition series. The other elements with partially filled d-subshell can undergo multiple metallic bonds . Thus the enthalpy of atomization in case of Zinc ix the lowest.
Silver atom has completely filled d-orbitals (4d10) in its ground state . how can you say that it is a transition metal ?
In case of silver , it involves the filling of outer 4d sub shell in its outer shell in its ground state. Moreover its ion is Ag+ . its outer configuration and its behavior matches with the d-block elements thus it is placed in transition metals.
Explain why molar conductivity for acetic acid can not be determined experimentally ?
Acetic acid is a weak electrolyte , and in case of weak electrolytes , their molar conductivity keeps on increasing on dilution . we can not achieve a constant value. Thus its is difficult to explain the molar conductivity of acetic acid.
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