EasyChemistryHigh School (11–12)Atoms and Molecules › The Mole Concept Atoms and Molecules › Molecules, Ions and FormulaeNumericalBoard Exam

Urea, CO(NH₂)₂, is a fertiliser. Find its molecular mass, with C = 12.01 u, O = 16.00 u, N = 14.01…

Contributed by StemPy Lab

Try it on paper first. A hint, the key idea and the worked solution are here when you need them.

Urea, $\text{CO(NH}_2)_2$ , is a fertiliser. Find its molecular mass, with $\text{C} = 12.01$ u, $\text{O} = 16.00$ u, $\text{N} = 14.01$ u and $\text{H} = 1.008$ u.

Need a reminder? The key ideaShow

One atomic mass unit, $1\ \text{u}$ , is one twelfth of the mass of a carbon-12 atom. The average atomic mass of an element is $\bar{A} = \dfrac{\sum m_i p_i}{100}$ , where $m_i$ is the mass of each isotope and $p_i$ its share in percent. The molecular mass, or the formula mass of an ionic compound, is the sum of the atomic masses of all the atoms in the formula.

The worked solution

Have you tried it?

Work it out on paper first. It is fine to get stuck or make a mistake: that is how we learn. When you are ready, go through the solution one step at a time, and check each step against your own.

← All Problems

← At 110 °C and a fixed pressure, Meera sparks 50 mL of hydrogen with 20 mL of oxygen…Silicon has three isotopes: silicon-28 of mass 27.977 u (92.23%), silicon-29 of mass 28.976 u… →

More onAtoms and Molecules › The Mole Concept Atoms and Molecules › Molecules, Ions and Formulae

Discussion (0)

Loading…

Urea, CO(NH₂)₂, is a fertiliser. Find its molecular mass, with C = 12.01 u, O = 16.00 u, N = 14.01…

The worked solution

Discussion (0)

Want to go further in Atoms and Molecules › The Mole Concept?