2010 - JAMB Chemistry Past Questions and Answers - page 1

A mixture is a substance made by mixing other substances together, and these substances are not chemically combined.

• A. Common salt (Sodium Chloride - NaCl) is a pure compound.
• B. Blood is a mixture of various components, including red blood cells, white blood cells, platelets, and plasma.
• C. Sand (Silicon dioxide - SiO2) is a pure compound.
• D. Washing soda (Sodium carbonate - Na2CO3) is a pure compound.

1. Determine the formula of calcium trioxonitrate (V): The formula is Ca(NO₃)₂.

2. Calculate the molar mass of Ca(NO₃)₂:

   • Ca: 1 x 40 = 40 g/mol
   • N: 2 x 14 = 28 g/mol
   • O: 6 x 16 = 96 g/mol
   • Total molar mass = 40 + 28 + 96 = 164 g/mol

3. Calculate the mass of nitrogen in Ca(NO₃)₂:

   • Mass of N = 2 x 14 = 28 g/mol

Nitrogen has an atomic number of 7. The electronic configuration is 1s²2s²2p³.

• The 1s and 2s orbitals are completely filled (each holding 2 electrons, paired).
• The 2p subshell has three orbitals (2px, 2py, and 2pz), each of which can hold up to 2 electrons. Hund's rule states that electrons will individually occupy each orbital within a subshell before pairing up in any one orbital.
• Therefore, the three electrons in the 2p subshell will each occupy one of the three p orbitals singly. This results in 3 unpaired electrons.