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Molar mass of potassium iodide (KI)

The molar mass of potassium iodide (KI) is 166.00277 g/mol, summed from the IUPAC standard atomic weights of K, I.

mol
Molar mass
166.002 77g/mol
= Exact Molar mass of potassium iodide
Moles in the sample mass
0.060 239 959 mol
Mass of that amount of substance
166.002 77
Molecules in the sample mass
3.62774e+22
Show the working
  1. Mass of sample = 10
  2. Amount of substance = 1
  3. Molar mass = 39.0983 + 126.90447 = 166.003
  4. Moles in the sample mass = 10 / 166.003 = 0.060 24
  5. Mass of that amount of substance = 1 * 166.003 = 166.003
  6. Molecules in the sample mass = 0.060 24 * NA = 3.62774e+22

Values are shown to six significant figures here; the arithmetic itself runs on exact fractions and is only rounded where a number is printed.

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    The formula

    • Molar mass = sum over elements of (atomic weight x number of atoms)
    • For KI: 39.0983 + 126.90447 = 166.00277 g/mol
    • Moles = mass / molar mass; mass = moles x molar mass
    • Molecules = moles x 6.02214076 x 10^23 (the Avogadro constant, exact by definition)

    Molar mass in grams per mole is numerically equal to the molecular mass in daltons, so this figure doubles as the molecular weight.

    Atomic weights are the IUPAC 2021 standard values. Several elements have a range rather than a single value because isotope ratios vary between sources; the conventional single value is used here.

    Composition by mass

    Element Atoms Atomic weight Contribution (g/mol) Share of mass
    Iodine (I) 1126.90447126.9044776.447 %
    Potassium (K) 139.098339.098323.553 %

    Contributions add to the molar mass of 166.00277 g/mol. Atomic weights are the IUPAC 2021 standard values.

    Frequently asked

    What is the molar mass of potassium iodide?

    166.00277 g/mol, for the formula KI.

    How do you convert grams of potassium iodide to moles?

    Divide the mass in grams by 166.00277 g/mol. One gram of potassium iodide is 0.006024 mol.

    How many grams are in one mole of potassium iodide?

    166.00277 g, by definition of the molar mass.

    Is molar mass the same as molecular weight?

    Numerically yes, for the purposes of this calculation. Molecular weight is a dimensionless ratio and molar mass carries units of g/mol, but the digits are identical.

    Where the numbers come from

    • IUPAC 2021 standard atomic weights; Avogadro constant fixed by the 2019 SI.

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