# Session 2: Mass ⚖️

It's difficult for me to set interactive puzzles for you, because there is no simple way for you to enter scientific notations, and you are not fluent enough with sig figs to get them right.

To work around this, use the "E" notation: enter 5.55 x 10³ as 5.55e3, and keep three sig fig for your answers.

How many neon atoms are in 0.500 mol of Ne atoms?

How many neon atoms are in 1000 mol of Ne atoms?

How many wheels are in 0.5 dozens of bicycles?

How many hydrogen atoms are in 0.500 mol of water molecules?

How many neutrons are in 0.500 mol ²H?

What is the alternative symbol for ²H?

How many neutrons are in 0.500 mol H₂?

One molecule can contain more than one atom, and one atom can contain more than one sub-atomic particle.

Unless specified, assume the most common isotope. ²H is also called deuterium, with the symbol D. This isotope gets its own symbol because it has so many important uses.

Identify the number of neutrons in ⁸¹Br.

The natural abundance of bromine is 51% ⁷⁹Br and 49% ⁸¹Br. What is the atomic mass of bromine?

Use your data booklet to find the atomic number of bromine.

Calculate the molar masses for each of the molecular formula you have done in the previous week. Round your answers to 3 or 4 sig fig. The answers are in the help section.

This is easy until the empirical formula is introduced. Then students get confused and calculate some meaningless number. To defend against that error, ask yourself the meaning of what you are trying to find, instead of memorizing a formula.