Chemistry 101 Term Test  #2

1. [5]  When heated, diaminoselenium, (NH₂)₂Se, decomposes  according to the equation

                (NH₂)₂Se(s)  -->  1/8Se₈(s)    +    N₂(g)    +   2H₂(g)

A sample of solid diaminoselenium, (NH₂)₂Se(s), was placed in an evacuated cylinder and heated to 300 degrees C, resulting in the formation of a mixture of molecular nitrogen, elemental selenium and molecular hydrogen gas. After twenty minutes of heating at 300 degrees C, the reaction reached equilibrium and the total pressure climbed to a maximum value of 8.44 atmospheres. Some solid diaminoselenium was still present in the cylinder at equilibrium. Use the information given to calculate K_p for the diaminoselenium decomposition reaction at 300 degrees C.

2. [6]   At elevated temperatures, potassium perchlorate decomposes to produce potassium hypochlorite and molecular oxygen gas. A 0.8988 g sample of  impure potassium perchlorate was heated until the production of molecular oxygen gas ceased.  A total 48.8 mL of molecular oxygen gas were collected in a buret over water at a temperature of 22.0 ^oC and a barometric pressure of 734 mm Hg. A water column 2.23 cm high was observed inside the buret.

a)      Write a balanced equation for the decomposition reaction.

b)      Calculate the mass percent of potassium perchlorate in the original sample.

3. [4]   A compressed gas cylinder contains 1.00 x 10³ grams of Ar and 8.20 x 10² grams of Ne. The pressure inside the cylinder is 148.8 atm. The internal volume for the cylinder is 17.8 L.

 a)    Calculate the partial pressure for the Ar gas in the cylinder.

b)  What is the temperature of the gaseous mixture in the cylinder?

4. [3]  Which of the following three p-block atoms, P, S or Cl , has

             a)  the smallest first ionization energy?

             b)  the smallest radius?

            c)  the largest effective nuclear charge. (Be sure to justify your answers)

5. [3]  Give the four quantum numbers for each electron in the valence shell

       of the N²⁺ ion.

6. [3]  Which transition-metal tri-cation has the electronic configuration [Xe]₅₄4f¹⁴5d⁸ ?  How many electrons are left unpaired in this ion?

7. [6]   Write down the complete electron configurations for the following neutral atoms.  Predict the three most stable ions/oxidation states for each atom (apart from the zerovalent state) and classify each ion/oxidation state according to its type. Lastly, give the abbreviated electronic configuration for each ion/oxidation state.

i)  Selenium

ii)  Antimony

8. [13]  Fill in each blank with the appropriate answer. 

i)  Which element has the higher first ionization energy:  N or O?

ii)  The anion with the smallest radius is _________________

iii)  The salt MnCl₂ is  _____________________ (diamagnetic/paramagnetic)

iv)  The Tc³⁺ ion has _______ unpaired electrons in its valence shell.

v)  Apart from Group 2 metals and transition metals, _______________ main-group metals can form stable 2+ ions. 

vi )  Hund’s rule states that the lowest energy electron configuration for an atom is the

vii)  As we go down a particular vertical group in the periodic table, the effective

         nuclear charge __________________________

viii)  What is the generalized valence shell electron configuration common to all of the

          halogens? 

  ix)  Identify the neutral element that is isoelectronic with the anion 

         As^3- 

x)      Provide the appropriate value for the missing quantum number :

n = 3, l = 0, m_l = _____?, m_s = -1/2. 

xi)   Max Planck found that energy can only be gained or lost in whole number multiples of _________________.

 xii)  The n = 3 shell of the hydrogen atom contains __________ f-orbitals.

xiii)  Which of the following isoelectronic ions has the largest radius?: 

            La³⁺, I^- or Te^{2- ?}

9. [3]   An unknown p-block element has the general valence shell electron configuration

            ns²np³.

a)      Would this element have a greater or smaller ionization energy than fluorine?

b)      What is the formula of the compound this element would form with Mg?

c)      Would this element have a larger or smaller radius than Ba?

Bonus Question (2 marks):

A beam of electrons and a beam of protons are moving with the same speed.  Which has the longer de Broglie wavelength?  Why?