# Session 2: Mass ⚖️
Moles as a Unit for Counting
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?
Isotopes and Atomic Mass
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?
Molar Mass
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.
# Homework
Read Section 1.2 and do the exercises in there. Keep doing your Anki decks.
Since there is a long weekend, we'll move this set of homework to Monday. Upload both Session 1 and Session 2 homework by (Mon) 21:00. This should take no more than 45 minutes.