Question

Calculate the molecular mass of caustic potash-
A. $K_2$OH = 95 $g{mol}^{-1}$
B. KOH = 56 $g{mol}^{-1}$
C. K(OH$)_2$ = 73 $g{mol}^{-1}$
D. KOH = 58 $g{mol}^{-1}$

Answer 1

: Hint: The molecular mass of caustic potash or potassium hydroxide (KOH) is found by knowing the molar masses of the elements.

Complete step-by-step solution -

From the periodic table we can find that the molar mass of potassium or K is 39.098 g/mole.
Similarly, the molar mass of O is found to be 15.999 g/mole from the periodic table.
And the molar mass of H is found to be 1.00784 g/mole.
We know the formula of caustic potash is KOH.
The molecular weight of caustic potash or KOH (potassium hydroxide) is = Molar mass of K + Molar mass of O + Molar mass of \[H{\text{ }} = {\text{ }}\left( {39.098{\text{ }} + {\text{ }}15.999{\text{ }} + {\text{ }}1.00784} \right){\text{ }}g/mole{\text{ }} = {\text{ }}56.10484{\text{ }}g/mole\]
$ \approx \;56{\text{ }}g/mole$
Therefore, we conclude that Option B is the correct answer.

Additional information:
Molar mass is defined as the mass in grams of one mole of a substance. The units of molar mass are grams per mole which is abbreviated as g/mole.
Molecular mass is a number which indicates how many times one molecule of a substance is heavier in comparison to 1/16th of the mass of oxygen atom or 1/12th mass of one atom of carbon-12.
M= Mass of one molecule of the substance/ 1/12th mass of one atom of carbon-12

Note: Potassium is the 19th element of the periodic table. It is located in period 4 and group 1. Oxygen is the 8th element of the periodic table. It is located in period 2, group 16. Hydrogen is placed above the periodic table as it has ns1 electronic configuration like the alkali metals, as well as it forms H-, which is hydride anion like the non-metals.