Chemistry Homework Solutions

This document presents solutions to a chemistry homework assignment. The solutions cover several topics, including determining the number of protons in an element given its mass number and number of neutrons, identifying the type of bond (polar covalent, non-polar covalent, or ionic) based on electronegativity differences, and explaining the solubility of NaCl in water and methanol. The solutions provide detailed explanations and calculations for each problem.

Answer 1.
(a.)
We know that,
Mass number is the sum of the number of proton and the number of neutrons
Therefore,
Number of the protons = Mass number - Number of neutrons
= 25 - 13
= 12
The atomic number of the element is equal to the number of protons = 12.
(b.)
c.) There are only two electrons in the outer most shell therefore the atom would prefer to lose
two of its electron and become a cation rather than gaining six electrons.
2.
(a.) If the electronegativity difference is zero then the bond is non-polar covalent. If the
difference between the electro negativities is more than zero but less than 2, then the bond is
polar covalent and if the difference between the electro negativities is more 2, then the bond is
ionic.

 Az- Ca: 3.8-2.7= 1.1. Therefore, the bond is polar covalent.
 Or-Mt: 2.0-1.3= 0.7. Therefore, the bond is polar covalent.
 Nv- Ca: 3.9-3.8= 0.1. The electro negativities are almost the same. Therefore, non-polar
covalent.
 Co-Az: 2.7-0.2= Therefore, the bond is ionic in nature.
(b.)
The Az-Ca and Or-Mt form polar covalent.
Az would have partial negative charge and Ca will have partial positive charge.
Similarly, Or will have partial negative charge and MT will have partial positive charge.
Question 3.
Question 4.
NaCl will dissolve in the beaker containing water due to the fact that NaCl is an ionic compound
and water is polar in nature. The polarity of the water molecules leads to higher solubility of the
ionically bonded substances. Salt being ionic is made from the positive sodium and negative
chloride ions. The positive part of the water molecule will attract towards the negative chloride
ions and similarly the negative part of the water molecules will attract to the positive sodium
ions. Therefore, NaCl will readily dissolve in the water.
Similarly, salt will dissolve in methanol due to the liquid being polar in nature. However, sodium
chloride will not dissolve in methanol not as readily as it did in the water.

Salt (you probably mean table salt or NaCl) is soluble in polar liquids. Methanol is a polar liquid and so
salt is soluble. It is more soluble in water since water is more soluble. Some optics for infrared equipment
are made of NaCl, and they can be polished with methanol without dissolving them too quickly.