Question

A sample contains 125 mg of NaCl and 45.0 mg of KCl. How many mmol of each ion are contained in the sample?

Answer 1

Number of moles of Nacl = weight in grams / Molar mass

Number of millimoles of Nacl = weight of Nacl in mg / molar mass

= 125mg / 58.5 g_/mol

= 2.1367 mmol

1 mmol of Nacl contains 1 mmol Na⁺ + 1 mmol of Cl^-

2.1367 mmol of Nacl contains

2.1367 mmol Na⁺   + 2.1367 mmol Cl^-

Number of millimoles of Kcl = weight of Kcl in mg / Molar mass

= 45 mg / 74.5513 g_/mol

= 0.603611 mmol.

0.603611 mmol of Kcl contains

0.603611 mmol K⁺   + 0.603611 mmol Cl^-

Cl^- = 0.603611 + 2.1367 = 2.740311 mmol

K⁺ = 0.603611 mmol

Na⁺ = 2.1367 mmol.