Question

Choose the correct answer.

The molecular mass of Potassium dihydrogen phosphate is ________________ .

• A. 136
• B. 140
• C. 152
• D. 135

Answer 1

The correct option is A

136

Calculation of molecular mass of potassium dihydrogen phosphate

• Molecular formula =${\mathrm{K}}^{+}{\mathrm{H}}_2{{\mathrm{PO}}_4}^{-}={\mathrm{KH}}_2{\mathrm{PO}}_4$
• Number of potassium atoms = 1 $\times$atomic mass of potassium = 1 $\times$ 39.098 = 39.098
• Number of hydrogen atoms = 2 $\times$ atomic mass of hydrogen = 2 $\times$ 1.008 =2.016
• Number of phosphorous atoms = 1 $\times$ atomic mass of phosphorous = 1 $\times$ 30.974=30.974
• Number of oxygen atoms = 4 $\times$atomic mass of oxygen = 4 $\times$ 15.999 = 63.996
• Total molecular mass of potassium dihydrogen phosphate = 39.098 + 2.016+ 30.974 + 63.996 = 136.084 g/mol

Therefore option (a) 136 is correct.