Question

Which of the following is true about KCl?
A. Its melting point is 768 deg C and its boiling point is 1411 deg C
B. Its melting point is 50 deg C and its boiling point is 1411 deg C
C. Its melting point is 768 deg C and its boiling point is 4000 deg C
D. Its melting point is 50 deg C and its boiling point is 101 deg C

Answer 1

Hint: KCl is potassium chloride, which is an ionic compound and an electrolyte. When transfer of electrons occur from a metal to a non – metal then ionic bonds are formed. These ionic bonds are strong in nature and affect the boiling and melting points adversely.

Complete answer:
Potassium chloride, KCl is an ionic compound formed from potassium cation and chloride anion. Ionic compounds are formed by the transfer of electrons from one compound to another. Since, potassium is a metal that has one electron in its outer shell, and chloride is a non – metal that has only one electron missing from its valence shell, it will readily take up the electron from potassium to form ionic bonds. Ionic bonds are a result of electron transfer, and hence they are strong bonds that require high melting and boiling points to break the bonds.
Among the given melting and boiling points, KCl has a melting point of $768{}^\circ C$ and a boiling point of $1411{}^\circ C$. This is the highest melting and boiling point from the given options. The boiling point will not be 4000 deg C as this much boiling point is of a very high range that will not be feasible in ionic compounds.
Hence, KCl has a melting point of $768{}^\circ C$ and a boiling point of $1411{}^\circ C$.

So, option A is correct.

Note:
Melting points of compounds can be determined in the lab by capillary method. This method uses a capillary tube in which the substance is placed which is then attached with a thermometer and dipped in a water bath at high temperature. Thus a temperature is noted when the substance is observed to be melted.