One molecule of water (H2 O) contains two atoms of hydrogen and one atom of oxygen. A hydrogen a

step 1 So in atomic unit mass, what is the mass of one water molecule? So we see that water molecule ha

One molecule of water (H2 O) contains two atoms of hydrogen...

One molecule of water $\left(\mathrm{H}_{2} \mathrm{O}\right)$ contains two atoms of hydrogen and one atom of oxygen. A hydrogen atom has a mass of 1.0 $\mathrm{u}$ and an atom of oxygen has a mass of 16 $\mathrm{u}$ , approximately. (a) What is the mass in kilograms of one molecule of water? (b) How many molecules of water are in the world's oceans, which have an estimated total mass of $1.4 \times 10^{21} \mathrm{kg} ?$

Key Concepts

Atomic Mass Unit (u)

The atomic mass unit is a standard unit of mass that is used to express the masses of atoms and molecules. It is defined as one-twelfth of the mass of a carbon-12 atom, and it provides a convenient scale for comparing atomic-level masses. Conversions from atomic mass units to kilograms are routinely used in calculations that bridge microscopic and macroscopic mass measurements.

Molecular Composition and Mass Calculation

Molecular composition involves identifying the types and numbers of atoms within a molecule, which is key to determining its overall mass. By summing the products of each atom's mass and the number of times it appears in the molecule, one can calculate the molecule's total mass. This process is essential for linking molecular-scale properties with measurable quantities in larger samples.

Avogadro's Number

Avogadro's number is a constant that defines the number of individual particles (such as atoms or molecules) in one mole of a substance, approximately 6.022 x 10^23. This concept is fundamental in chemistry for converting between the mass of a single molecule and the collective mass of a mole, facilitating a connection between microscopic properties and macroscopic amounts.

Scientific Notation and Unit Conversion

Scientific notation is a method of writing very large or very small numbers in a compact form that simplifies calculations and improves clarity in data representation. Unit conversion, especially from atomic scale units like the atomic mass unit to kilograms, is crucial for accurately relating molecular-scale measurements to the quantities encountered in everyday life and industry.

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