Using molar mass to relate amount in moles and mass
4He atoms are one-third as heavy as 12C atoms so 1 mole of 4He atoms must weigh 4.0 g.
Molar mass (M) is the mass in grams per mole of an entity. This quantity has the unit g mol–1.
The magnitude of the molar mass for an atom equals the mass number.
The mass number is the larger of the two numbers in the element symbol box in the periodic table.
The molar mass (M) of helium is 4.0 g mol-1.
m = n × M
g = mol × g mol-1
A balloon contains 0.60 mol of helium. What is the mass of helium in the balloon?
m(He) = 0.60 mol × 4.0 g mol-1 = 2.4 g
To help remember how to combine amount in moles (n) and molar mass (M ) to give mass (m), note that multiplying the units of n and M gives the unit of mass.
m(He) = 0.60 mol × 4.0 g mol-1 = 2.4 g
To help remember how to combine amount in moles (n) and molar mass (M ) to give mass (m), note that multiplying the units of n and M gives the unit of mass.
Molar mass is VERY important because it can be used to relate a measureable property of a sample (mass) to the number of atoms, ions, or molecules present in a sample.
For substances that exist as entities containing more than one atom, the molar mass is equal to the sum of the molar masses of the component atoms.
Elemental hydrogen is also used to fill balloons.
M(H2) = 2 × M(H) = 2×1.0 g mol–1
Note that hydrogen is an exception to the guideline that the mass number is larger than the atomic number. In this one case, the mass number and the atomic number are equal because the most abundant isotope hydrogen has no neutrons.
The particles in elemental hydrogen are H2.
M(H2) = 2 × M(H) = 2×1.0 g mol–1
Note that hydrogen is an exception to the guideline that the mass number is larger than the atomic number. In this one case, the mass number and the atomic number are equal because the most abundant isotope hydrogen has no neutrons.