Nitrogen and Sulfur

Sample questions

Showing 10 of 70 questions from this chapter. The full bank is in the chapter test below.

1. 1

   What is the electronic configuration of a nitrogen atom?

   • A.✓ 1s2 2s2 2p3 (correct answer)
   • B.1s2 2s2 2p4
   • C.1s2 2s2 2p5
   • D.1s2 2s2 2p6

   Why: Nitrogen has atomic number 7 and five valence electrons, giving 1s2 2s2 2p3. It needs three more electrons to complete its octet.
2. 2

   Nitrogen is unreactive at room temperature mainly because:

   • A.Its molecule is nonpolar, so it cannot approach other molecules
   • B.✓ Its triple bond has a bond enthalpy of 944 kJ/mol (correct answer)
   • C.It has the highest first ionization energy of all the elements
   • D.Its molecules are heavier than oxygen molecules in air

   Why: Breaking the nitrogen triple bond needs 944 kJ/mol, so a large amount of energy must be supplied before nitrogen can form new bonds. Lack of polarity adds to the inertness but is not the main reason.
3. 3

   The bond enthalpy of the nitrogen triple bond is 944 kJ/mol. How much energy is required to break all the bonds in 0.25 mol of $\ce{N2}$ molecules?

   • A.118 kJ
   • B.189 kJ
   • C.✓ 236 kJ (correct answer)
   • D.944 kJ

   Why: Energy = 0.25 mol x 944 kJ/mol = 236 kJ. Taking the inverse ratio (944 / 0.25) wrongly gives 3776 kJ.
4. 4

   In the laboratory, a small quantity of nitrogen gas is obtained by gently heating an aqueous solution of:

   • A.ammonium chloride
   • B.ammonium sulfate
   • C.sodium nitrite
   • D.✓ ammonium nitrite (correct answer)

   Why: $\ce{NH4NO2(aq)}$ gives $\ce{N2(g)}$ + 2H2O(l). The other ammonium salts do not decompose in this way, and heating a nitrite alone gives oxides of nitrogen rather than $\ce{N2}$.
5. 5

   Liquid nitrogen is preferred for rapid cooling in food transport and in medicine because it:

   • A.Dissolves grease and other fats very quickly
   • B.✓ Boils at -195.8 °C and is chemically inert (correct answer)
   • C.Freezes water without coming into contact with it
   • D.Releases nitrogen gas that displaces oxygen

   Why: Nitrogen boils at -195.8 °C, so liquid nitrogen takes up heat very rapidly, and being inert it does not react with the material being cooled.
6. 6

   When ammonium nitrite decomposes according to $\ce{NH4NO2(aq) -> N2(g) + 2H2O(l)}$, how many moles of water are produced from 3.0 mol of ammonium nitrite?

   • A.1.5 mol
   • B.3.0 mol
   • C.✓ 6.0 mol (correct answer)
   • D.12.0 mol

   Why: The equation gives 2 mol of water for every mole of $\ce{NH4NO2}$, so 3.0 mol x 2 = 6.0 mol. Dividing by 2 instead of multiplying gives the wrong 1.5 mol.
7. 7

   Which equation represents the industrial manufacture of ammonia by the Haber-Bosch process?

   • A.$\ce{N2(g) + 2H2(g) -> N2H4(g)}$
   • B.$\ce{2N2(g) + 3H2(g) -> 2NH3(g)}$
   • C.$\ce{N2(g) + 3H2O(g) -> 2NH3(g) + O2(g)}$
   • D.✓ $\ce{N2(g) + 3H2(g) <=> 2NH3(g)}$ (correct answer)

   Why: Ammonia is made by the reversible combination of nitrogen and hydrogen in the ratio 1:3. The other equations are either unbalanced or not the Haber-Bosch reaction.
8. 8

   Ammonia is described as a Bronsted-Lowry base because it:

   • A.✓ Accepts a proton from an acid using the lone pair on nitrogen (correct answer)
   • B.Releases hydroxide ions when it dissolves in water
   • C.Donates a proton to any acid present in the solution
   • D.Accepts an electron pair from the acid molecule

   Why: A Bronsted-Lowry base is a proton acceptor, and ammonia uses the lone pair of its nitrogen atom to take up $\ce{H+}$ and form $\ce{NH4+}$. Hydroxide ions appear only as a result of this proton transfer.
9. 9

   The base ionization constant of ammonia in water is $K_{b}$ = $1.8 \times 10^{-5}$. What does this value show about ammonia?

   • A.It is fully ionized and behaves as a strong base
   • B.The equilibrium lies to the right, so it is a strong base
   • C.✓ The equilibrium lies far to the left, so it is a weak base (correct answer)
   • D.It is a weaker base than water itself

   Why: A small $K_{b}$ shows that only a small fraction of the ammonia molecules accept protons, so the equilibrium lies far to the left and ammonia is a weak base.
10. 10

    What is the shape of the ammonium ion, $\ce{NH4+}$?

    • A.Linear
    • B.Pyramidal
    • C.Triangular planar
    • D.✓ Tetrahedral (correct answer)

    Why: In $\ce{NH4+}$ the lone pair of nitrogen is used to form a fourth bond, so the four $\ce{N-H}$ bonds are equal in length and point towards the corners of a tetrahedron.