# What is the molar mass of helium gas?

Nathalie

The molar mass of helium gas is 4.002602 u.

Helium is a chemical element with symbol He and atomic number 2. It is a colorless, odorless, tasteless, non-toxic, inert, monatomic gas, the first in the noble gas group in the periodic table. Its boiling point is the lowest among all the elements. helium has several isotopes (different forms of the same element with an equal number of protons and electrons, but not neutrons), but generally has a molar mass of 4 grams/mole.

Molar mass is the mass of a given substance divided by the amount of that substance, measured in g/mol. For example, the atomic mass of titanium is 47.88 amu or 47.88 g/mol. In 47.88 grams of titanium, there is one mole, or 6.022 x 1023 titanium atoms.

The characteristic molar mass of an element is simply the atomic mass in g/mol. However, molar mass can also be calculated by multiplying the atomic mass in amu by the molar mass constant (1 g/mol). To calculate the molar mass of a compound with multiple atoms, sum all the atomic mass of the constituent atoms.

For example, the molar mass of NaCl can be calculated for finding the atomic mass of sodium (22.99 g/mol) and the atomic mass of chlorine (35.45 g/mol) and combining them. The molar mass of NaCl is 58.44 g/mol.

Example 1

What is the molar mass of sodium hydroxide?

Solution

The molar mass of sodium hydroxide NaOH is 39.997 g/mol

(23×1 Na) + (16×1 O)+ (0.997×1) = 39.997 g/mol

Example 2

What is the molar mass of Sodium Oxide ?

Solution

Molar mass of sodium oxide NaO is 61.9789 g/mol

(23×1 Na) + (16×1 O) = 61.9789 g/mol

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Related Questions
##### 2. (11 marks) a) At 400 °C, ammonium iodide decomposes in the following endothermic reaction: NH41(s) + NH3(g) + HI(g) Kp = 0.215 at 400 °C. Write the equilibrium expression for this reaction. 15.0 g of NH4I was placed in an empty 3.0 L flask and heated to 400 °C. What is the partial pressure of NH3 in the flask once the reaction has reached equilibrium? How would the following changes to the equilibrium mixture affect the number of moles of NH3 in the flask and the value of K, once equilibrium is re-established? (Use increase, decrease or stay the same.) Change Effect on moles of NH3 Ke value Increase temperature Increase volume of flask Remove half of HI gas
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