Sign in
12thPass logo
New chatPYQ LibraryDoubtsRank report
Sign in to see Recents

Your guest activity stays on this device

Sign in to save progress →
Sign in

P Block Elements question

2008 · Shift 1 · Q20
Guest · filters and generic practice availableBrowsing as a guest · PYQ filters and generic practice are available. Sign in only for personalised features and saved progress.
  1. PYQ Library
  2. /JEE Advanced
  3. /Chemistry
  4. /P Block Elements
  5. /2008 · Shift 1 · Q20

P Block Elements question

2008 · Shift 1 · Q20

JEE AdvancedChemistryP Block ElementsMCQ+3 / −1
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. Hybridisation easily explains the ease of sigma donation capability of NH 3{}_33​ and PH 3{}_33​. Phosphine is a flammable gas and is prepared from white phosphorus.White phosphorus on reaction with NaOH gives PH 3{}_33​ as one of the products. This is a:
  1. A
    dimerisation reaction
  2. B
    disproportionation reaction
  3. C
    condensation reaction
  4. D
    precipitation reaction
View written solutionFree

Correct answer: B

The user wants to identify the type of reaction when white phosphorus reacts with NaOH.

Step 1: Write the balanced chemical equation for the reaction.

The reaction of white phosphorus (P₄) with a hot concentrated solution of sodium hydroxide (NaOH) is a well-known preparation method for phosphine (PH₃).

The balanced chemical equation is: P4(s)+3NaOH(aq)+3H2O(l)→PH3(g)+3NaH2PO2(aq)P_4(s) + 3NaOH(aq) + 3H_2O(l) \rightarrow PH_3(g) + 3NaH_2PO_2(aq)P4​(s)+3NaOH(aq)+3H2​O(l)→PH3​(g)+3NaH2​PO2​(aq)

The products are phosphine (PH₃) and sodium hypophosphite (NaH₂PO₂).

Step 2: Determine the oxidation state of phosphorus in the reactant.

In the reactant, we have white phosphorus, which is an elemental form of phosphorus, denoted as P₄. In its elemental state, the oxidation number of any atom is 0.

  • Oxidation state of P in P₄ is 0.

Step 3: Determine the oxidation states of phosphorus in the products.

We have two products containing phosphorus: phosphine (PH₃) and sodium hypophosphite (NaH₂PO₂).

  • In phosphine (PH₃): The oxidation state of hydrogen is generally +1 when bonded to non-metals. Let the oxidation state of phosphorus be 'x'. x+3(+1)=0x + 3(+1) = 0x+3(+1)=0 x=−3x = -3x=−3 So, the oxidation state of P in PH₃ is -3.

  • In sodium hypophosphite (NaH₂PO₂): The oxidation state of Na is +1, H is +1, and O is -2. Let the oxidation state of phosphorus be 'y'. (+1)+2(+1)+y+2(−2)=0(+1) + 2(+1) + y + 2(-2) = 0(+1)+2(+1)+y+2(−2)=0 1+2+y−4=01 + 2 + y - 4 = 01+2+y−4=0 y−1=0y - 1 = 0y−1=0 y=+1y = +1y=+1 So, the oxidation state of P in NaH₂PO₂ is +1.

Step 4: Analyze the changes in oxidation state and classify the reaction.

We observe that the oxidation state of phosphorus changes from 0 in the reactant (P₄) to two different oxidation states in the products:

  • Reduction: The oxidation state of P decreases from 0 to -3 (in PH₃).
  • Oxidation: The oxidation state of P increases from 0 to +1 (in NaH₂PO₂).

A reaction in which a single element from a particular oxidation state is simultaneously oxidized and reduced is called a disproportionation reaction.

Step 5: Evaluate the given options.

  • A: Dimerisation reaction: This involves the combination of two identical molecules to form a single, larger molecule (a dimer). This is not happening here.
  • B: Disproportionation reaction: This matches our analysis perfectly. The phosphorus atom is both oxidized and reduced.
  • C: Condensation reaction: This typically involves the joining of two molecules with the elimination of a small molecule like water. This is not the case here.
  • D: Precipitation reaction: This involves the formation of an insoluble solid (precipitate). In this reaction, phosphine is a gas and sodium hypophosphite is soluble in water. No precipitate is formed.

Therefore, the reaction of white phosphorus with NaOH is a classic example of a disproportionation reaction.

PreviousNext

More from P Block Elements

  • Statement 1 : In water, orthoboric acid behaves as a weak monobasic acid. Statement 2 : In water, orthoboric acid acts as a proton donor.2007 · MCQ
  • The noble gases have closed-shell electronic configuration and are monoatomic gases under normal conditions. The low boiling points of the lighter noble gases are due to weak dispersion forces between the atoms and the absence of other…2007 · MCQ
  • The noble gases have closed-shell electronic configuration and are monoatomic gases under normal conditions. The low boiling points of the lighter noble gases are due to weak dispersion forces between the atoms and the absence of other…2007 · MCQ
  • The noble gases have closed-shell electronic configuration and are monoatomic gases under normal conditions. The low boiling points of the lighter noble gases are due to weak dispersion forces between the atoms and the absence of other…2007 · MCQ
  • The percentage of p-character in the orbitals forming P-P bonds in P 4 is2007 · MCQ
  • STATEMENT-1 : Band gap in germanium is small. STATEMENT-2 : The energy gap of each germanium atomic energy level is infinitesimally small.2007 · MCQ
  • The heating of NH4​NO2​ at 60–70 °C and NH4​NO3​ at 200–250 °C is associated with the formation of nitrogen containing compounds X and Y, respectively. X and Y, respectively, are2025 · MCQ
  • The complete hydrolysis of ICl, ClF3​ and BrF5​, respectively, gives :2025 · MCQ