Question: On first glance, both table salt, \[NaCl\] and ordinary table sugar, sucrose, \[{{C}_{12}}{{H}_{22}}...

Question

On first glance, both table salt, $NaCl$ and ordinary table sugar, sucrose, ${{C}_{12}}{{H}_{22}}{{O}_{11}}$ appear very similar; both are white, crystalline solids. Of the four possibilities listed below, which one would be a useful test to distinguish between table salt and sucrose? Tasting of chemicals in the laboratory is never an option, so it has not been included.
a.) Test electrical conductivity in solid state
b.) Test to see if the solid is water soluble or not
c.) Test electrical conductivity in aqueous solution
d.) Test the pH of an aqueous solution of the substance.

Answer 1

Solution

To solve this, remember that $NaCl$ is an electrolyte whereas ordinary table sugar, sucrose, ${{C}_{12}}{{H}_{22}}{{O}_{11}}$ is a nonelectrolyte. Try to recall the property that makes an electrolyte different from a non-electrolyte in a solution. Using this you can easily find the correct option from the given options.

Complete step by step answer:
It is known to you that table salt, $NaCl$ is a white crystalline ionic compound which is made up of $N{{a}^{+}}$ and $C{{l}^{-}}$ ions, which is obtained when $NaCl$ is either melted or dissolved in water to make aqueous solution.
However, ordinary table sugar, sucrose, ${{C}_{12}}{{H}_{22}}{{O}_{11}}$ is an example of a type of sugar which is known as disaccharide. This means it consists of two simpler forms of sugar (monosaccharide) and it is soluble in water and remains as it is without any association or dissociation.
Now, the test which would be useful to distinguish between table sugar and sucrose can be easily found by inspecting each of the given options:

Option A: In solid state, both ordinary salt and sucrose do not show electrical conductivity as ions in ordinary salt cannot move and sucrose does not contain any ions. So, option A is not correct.

Option B: Both ordinary salt and sucrose are white crystalline solid and are soluble in water. So, option B is also not correct.

Option C: In aqueous solution, ordinary salt shows electrical conductivity due to the presence of mobile ions whereas sucrose does not show electric conductivity as no ions are present in it. So, option C is the correct option.

Option D: Both have some pH of their aqueous solution. So, option D is also not correct.
Therefore, from above we can conclude that option C. test electrical conductivity in aqueous solution is the correct option.So, the correct answer is “Option C”.

Note: Electrolytes conduct electricity due to presence of ions in them. They are able to conduct electricity due to the mobility of free anions and cations in them. Nonelectrolytes do not conduct electricity.
Generally, all ionic compounds are electrolytes and non-ionic compounds are not. In the given question, the table salt is an ionic compound i.e. the anion and cation are bonded through an ionic bond which is a strong electrostatic force of attraction between the two oppositely charged ions. In sugar, the atoms are covalently bonded which do not give electrolytes upon solvation.