IIT-JEE 2008 · Paper 1 · Chemistry Q65

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ChemistrySingle correct+4 / -1Question 65 of 69

Passage

Paragraph for Question Nos. 64 to 66

There are some deposits of nitrates and phosphates in earth's crust. Nitrates are more soluble in water. Nitrates are difficult to reduce under the laboratory conditions but microbes do it easily. Ammonia forms large number of complexes with transition metal ions. Hybridization easily explains the ease of sigma donation capability of $\ce{NH3}$ and $\ce{PH3}$ . Phosphine is a flammable gas and is prepared from white phosphorous.

Among the following, the correct statement is

Between

\ce{NH3}

and

\ce{PH3}

\ce{NH3}

is a better electron donor because the lone pair of electrons occupies spherical 's' orbital and is less directional

Between

\ce{NH3}

and

\ce{PH3}

\ce{PH3}

is a better electron donor because the lone pair of electrons occupies

sp^3

orbital and is more directional

Between

\ce{NH3}

and

\ce{PH3}

\ce{NH3}

is a better electron donor because the lone pair of electrons occupies

sp^3

orbital and is more directional

Between

\ce{NH3}

and

\ce{PH3}

\ce{PH3}

is a better electron donor because the lone pair of electrons occupies spherical 's' orbital and is less directional

Answer and worked solution

Official answer: C

Lone pairs. In $\ce{NH3}$ the lone pair is in an $sp^3$ orbital, directional and well suited to σ donation. In $\ce{PH3}$ the bond angle is near 90°, so P uses almost pure p orbitals for bonding and the lone pair has largely s character: spherical, diffuse and a poor donor.

So $\ce{NH3}$ is the better electron donor because its lone pair is in a directional $sp^3$ orbital.

(C)

Topics:Group 15 Hybridisation

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IIT-JEE 2008 · Paper 1, Chemistry question 65