JIPMER Entrance Chemistry Flashcards

24 sample cards from the Chemistry deck

Sampled from the end of the deck, so these are different cards from the ones shown on the syllabus page.

1. State Raoult's law for a solution of a non-volatile solute.

   The relative lowering of the vapour pressure of a solvent is equal to the mole fraction of the non-volatile solute. (p0 - p)/p0 = mole fraction of solute.

2. How do atomic radius and ionisation energy vary across a period and down a group?

   Across a period (left to right): atomic radius decreases, ionisation energy increases. Down a group: atomic radius increases, ionisation energy decreases.

3. Define electronegativity and name the most electronegative element.

   Electronegativity is the tendency of an atom to attract the shared pair of electrons in a covalent bond towards itself. Fluorine is the most electronegative element (4.0 on the Pauling scale).

4. What is the cause of the lanthanide contraction and one consequence?

   Lanthanide contraction is the steady decrease in atomic and ionic size across the lanthanide series due to poor shielding by 4f electrons. A consequence is that the second and third transition series elements (e.g. Zr and Hf) have nearly identical sizes.

5. State VSEPR theory and predict the shape of methane (CH4).

   VSEPR (Valence Shell Electron Pair Repulsion) theory states that electron pairs around a central atom arrange themselves to minimise repulsion. CH4 has four bonding pairs and no lone pairs, giving a tetrahedral shape with bond angles of 109.5 degrees.

6. Differentiate between sigma and pi bonds.

   A sigma bond forms by head-on (axial) overlap of orbitals and is stronger; a pi bond forms by sidewise (lateral) overlap of p orbitals and is weaker. A single bond is one sigma; a double bond is one sigma + one pi; a triple bond is one sigma + two pi.

7. What types of hybridisation correspond to linear, trigonal planar, and tetrahedral geometries?

   sp hybridisation gives linear (180 degrees), sp2 gives trigonal planar (120 degrees), and sp3 gives tetrahedral (109.5 degrees) geometry.

8. Why does ice float on water (in terms of bonding)?

   In ice, hydrogen bonding arranges water molecules in an open, cage-like crystalline structure with more empty space, making ice less dense than liquid water, so ice floats.

9. Why are alkali metals strong reducing agents and stored under kerosene?

   Alkali metals (Group 1) have low ionisation energies and readily lose their single valence electron, making them strong reducing agents. They are highly reactive with air and water, so they are stored under kerosene to prevent reaction with moisture and oxygen.

10. What is the diagonal relationship and give one example pair.

    The diagonal relationship is the similarity in properties between an element of one group and the element diagonally placed to it in the next group and period, due to similar charge/size ratios. Example: lithium resembles magnesium (also beryllium-aluminium, boron-silicon).

11. Why is the +1 oxidation state more stable than +3 for thallium (inert pair effect)?

    Down Group 13, the inert pair effect causes the two ns electrons to be reluctant to participate in bonding because of poor shielding by d and f electrons. So for heavy elements like Tl, the +1 state (retaining the ns2 pair) is more stable than +3.

12. Why do transition metals exhibit variable oxidation states and form coloured compounds?

    They show variable oxidation states because the energies of the (n-1)d and ns electrons are close, so both can be involved in bonding. Their compounds are coloured due to d-d electronic transitions that absorb visible light.

13. State Werner's coordination theory in brief and define coordination number.

    Werner's theory says metals have two valencies: primary (ionisable, satisfied by negative ions) and secondary (non-ionisable, satisfied by ligands, fixed and directional, giving geometry). Coordination number is the number of ligand donor atoms directly bonded to the central metal ion.

14. What is a chelate and why are chelate complexes more stable (chelate effect)?

    A chelate is a complex formed when a polydentate ligand binds to a central metal ion through two or more donor atoms, forming a ring. Chelate complexes are more stable than those with comparable monodentate ligands due to the favourable entropy increase, known as the chelate effect.

15. What is the difference between roasting and calcination in metallurgy?

    Roasting is heating an ore (usually a sulphide) strongly in the presence of air to convert it to oxide. Calcination is heating an ore (usually a carbonate or hydroxide) in the absence or limited supply of air to drive off volatile matter and form the oxide.

16. What is the role of a flux and the slag formed in metallurgy?

    A flux is a substance added during smelting that combines with the infusible gangue (impurities) to form a fusible, easily removable product called slag. The slag, being lighter, floats on the molten metal and is removed.

17. What is the principle of froth flotation and which ores does it concentrate?

    Froth flotation concentrates sulphide ores by exploiting the difference in wettability: powdered ore is mixed with oil and water; sulphide particles cling to oil/air bubbles and rise as froth, while gangue settles down with water.

18. Why is hydrogen called a unique element and what are its three isotopes?

    Hydrogen is unique because it resembles both alkali metals (forms H+) and halogens (forms H-, needs one electron to fill its shell), so its position is anomalous. Its three isotopes are protium (1H), deuterium (2H), and tritium (3H).

19. Explain the difference between temporary and permanent hardness of water.

    Temporary hardness is due to dissolved bicarbonates of calcium and magnesium and can be removed by boiling. Permanent hardness is due to dissolved chlorides and sulphates of calcium and magnesium and cannot be removed by boiling; it requires methods like ion exchange or adding washing soda.

20. State Markovnikov's rule for addition to alkenes.

    When a protic acid HX adds to an unsymmetrical alkene, the hydrogen attaches to the carbon already bearing more hydrogen atoms, and the X (halogen) attaches to the carbon with fewer hydrogens. This is because the more stable carbocation forms.

21. What is the difference between an electrophile and a nucleophile?

    An electrophile is an electron-deficient, electron-pair-accepting species (e.g. H+, NO2+, carbocations). A nucleophile is an electron-rich, electron-pair-donating species (e.g. OH-, CN-, NH3).

22. What are the +I and -I inductive effects?

    The inductive effect is the permanent partial shift of sigma-bond electrons along a carbon chain. +I (electron-releasing) groups push electron density (e.g. alkyl groups). -I (electron-withdrawing) groups pull electron density (e.g. -NO2, -COOH, halogens).

23. Define structural isomerism and name its main types.

    Structural (constitutional) isomerism is when compounds have the same molecular formula but different arrangements of atoms. Main types: chain isomerism, position isomerism, functional group isomerism, metamerism, and tautomerism.

24. Name the reagent for distinguishing aldehydes from ketones and the observation for aldehydes.

    Tollens' reagent (ammoniacal silver nitrate) and Fehling's solution are used. Aldehydes give a positive test: Tollens' gives a silver mirror, and Fehling's gives a brick-red precipitate of Cu2O. Ketones (except alpha-hydroxy) do not react.

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