Chemistry
What is an alloy ?
It is a homogenous mixture of metals . sometime a small quantity of non metal is also added in it . for example steel , brass and bronze.
Which transition metal of 3-d series exhibits the largest number of oxidation states and why ?
Manganese exhibit largest number of oxidation states, because it has highest number of unpaired electrons. here is the example.
Explain why Cu ion is stable in aqueous solution ?
The enthalpy of hydration of Cu+2 is enough negative which can easily compensate the second ionisation energy of copper. That is why Cu+2 ions are more stable in the aqueous solution.
What are inner transition metals ?
The elements in which the last electron is filled in f-subshell are called inner transition metals. These are also known as f-block elements.
What are lanthanoids ?
These are the elements in which the outermost electron is filled in 5f-subshell.
What are actenoids?
The elements from atomic number 89 (Actinium) to 103 Lawrencium, involving the filling of 5f-subshell.
How many orbitals are incomplete in inner transition elements ?
In case of inner transition elements there are three incomplete orbitals. these are s, d , and f .
What is lanthanoid contraction ?
It the phenomenon in which the atomic radii of elements decrease from Lanthanum to Lutetium. Or more simply it is the decrease in atomic radii when we move from La to Lu .
The radii of 2nd second transition series and 3rd third transition series are very similar , why ?
This is because of the lanthanoid contraction as in case of 3rd transition series, the filling of f-subshell takes place. The screening effect of f-subshell is least . Due to this the effective nuclear charge experienced by 3rd transition series is quite high. The increase in size due to increase in shell numbers is overcame
Atomic radii of Zr(160pm) is identical with radii of Hf (159pm) why ?
It is due to the lanthanoid contraction.
Zr and Hf occur together in nature why ?
In case of Zr and Hf the lanthanoid contraction takes place which accounts for the similar atomic size and because of similar size they are found together.
Explain why the separation of Zr and Hf from a mixture is difficult ?
The atomic radii of both the elements is similar, due to which their physical properties also match. so these are very difficult to separate by physical methods.
The first two ionisation enthalpies of Lanthanoids are comparable to calcium Ca . Explain how.
The lanthenoids show the following configuration :- Ln – 4f 1-14 5 s2 5s6 6s2 And configuration of Calcium is :- Ca- [Ar] 4s2 In both of the cases there are 2 electrons in outer s-subshell. Thus ionisation enthalpies of lanthenoids are comparable to the Calcium.
Name the lanthanoids that show very low value of third ionisation enthalpy.
Europium is the element that shows very low value of third ionisation enthalpy.
What is mischmetal ?
Mischmetal is an alloy having the following components:- Lanthenoids 95% Iron 5% Traces of Sulphur , Carbon , Calcium and Aluminium
What are the uses of mischmetal ?
The uses of mischmetal are :- To produce bullets Lighter flint Shells
Which compound is used as phosphors in T.V. screens ?
Lanthanoid oxide is the compound used as phosphors in T.V. screen.
Give one use of mixed oxides of lanthanoids.
The mixed oxides of lanthanoids are used in the cracking of petrolium .
Name the actenoid element from which the electrons starts filling 5f sub shell.
Protactinium (Pa) is the element that starts the filling of 5f subshell.
What is actinoid contraction ?
It is the phenomenon of regular decrease in size as we move from Actinium to Lawrencium due the poor shielding effect of f- subshell.
What is the most common oxidation state shown by actinoids ?
The most common oxidation state shown by the actinoids is +3
What is the maximum oxidation state shown by actinoides ?
Maximum or highest oxidation state of actinoids is +4.
What is the minimum oxidation State Shown by lanthenoids ?
Minimum oxidation state shown by the lanthenoids is +2 .
Name the components of steel.
The components of steel are :- Iron = 95% Carbon = 5% Chromium Manganese Nickel
Name the transition metal compound used in pigment industry.
Titanium oxide (TiO) is the compound used in the pigment industry.
Which compound of transition metal is used in dry cell ?
The compound used in dry cell is manganese oxide (MnO2)
What is the highest oxidation state shown by lanthenoids ?
+4 is the highest oxidation state shown by the lanthenoids.
Name the transition metal used in battery industry.
Nickel and Cadmium are the two metals which are used in the large scale battery production.
What are the coinage metals ? Why they are called so?
Copper , Silver and Gold (elements of group 11) are known as the coinage metals as they were used in making coins in the older times.
Name the compound used in Wacker process of oxidation of ethyne to ethanol.
In Wacker’s process PdCl2 is used for oxidation of ethyne to ethanol .
In which industry silver bromide (AgBr) is used ?
Silver bromide is used in photography. This due to the fact that AgBr readily decomposes to Ag and Br on exposure to light.
Complexes of which transition metal are useful in the polymerisation of alkynes ?
Complexes of Nickel are useful in polymerisation of alkynes .
What is the lowest common oxidation state of transition metals ?
+2 is the lowest common oxidation state of transition metals.
why soda water and soft drinks are packed sealed under high pressure ?
The soft drinks and soda water are packed under high pressure.
Explain the term ‘Mole fraction’ .
It the ratio of number of moles of a perticular component to the total number of moles of components present in the mixture .
How does the molarity of solution changes with change in temperature ?
With change in temperature the volume of solvent increases ,due to this the molarity of the solution decreases.
Why is molality is preferred over molarity if the solution ?
Molarity : It decreases with increase in temperature. Molality : It remains constant . Doesn’t change. In the light of above points it is clear that any change in temperature can bring change in concentration of the solution.
Why does the molality remains unchanged unaffected with change in temperature ?
Because the mass do not vary with change in temperature. It remains the same.
Which concentration term remains unaffected by temperature ?
Molality remains unaffected with any change in temperature. This is due to the fact that it uses the mass of solvent in Kilograms instead of volume in litres.
NaCl is soluble in water but not in benzene . Why ?
Benzene is a non polar solvent and salt is polar in nature . Thus it is not soluble in benzene , whereas in case of water , water and salt both are polar in nature so it is soluble in water.
How is that alcohol and water are miscible in all proportions ?
It is because of the fact that the water and alcohol are polar in nature . Moreover they make Hydrogen bonds, which are a type of weak attraction which facilitates their mixing in all proportions. The following diagram depicts that :-
Oil and water don’t mix . why ?
It can be explained on the basis of simple fact that like dissolves like. Oil is non polar liquid where as water is polar liquid so these do not mix.
Is smoke a homogeneous solution ?
No , smoke is not a homogeneous solution . as the particle size of dispersed phase is larger it belongs to the colloidal mixture.
What is the formula of DDT and what are its uses ?
Dichlorodiphenyltrichloroethane is an insecticide. It is banned in various countries . It is useful in killing various insects especially malaria causing mosquito.
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
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