Chemical Equations Quizzes
Podcasts on chemical equations, molar mass, and stoichiometry for review:
Some documents you might need:
- WebElements Periodic Table (I use the 5-figure version)
Polyatomic Ions
The values for the molar masses depend upon how many significant figures you use. For example, in my CHEM 1090 and CHEM 1100 classes (General Chemistry I and II), students add up the molar masses for each element in the chemical formula and then round to the appropriate number of decimal places based on the element which has the least number of decimal places. On the other hand, in my CHEM 1050 class (Chemistry and the Citizen) students round the molar mass for each element in the chemical formula to one decimal place and then add them up.
Using calcium hydroxide, Ca(OH)2, as an example:
Ca: 40.078 g/mol, O 15.999 g/mol, and H 1.008 g/mol.
For my CHEM 1090/1100 classes: 74.092 g/mol (summed and rounded to 3 decimal places because of calcium and oxygen).
For my CHEM 1050 class: 74.1 g/mol (each one arbitrarily rounded to 1 decimal place and then summed up).
It is also appropriate to use the complete, unrounded molar mass for any calculations like conversions between mass and moles. Until I alter the quizzes to allow for all of the decimal places, any molar mass used in a calculation will follow the previously stated decimal place rules.
Important: If you want or need to enter your answer using scientific notation, you’ll need to enter it a certain way. For example, 1.254 x 10-8 would be entered as 1.254e-8.
Remember that the e is computer lingo for x 10
When you balance a chemical equation, you need to use smallest whole numbers and no fractions or it will be marked incorrect. I will alter the quiz in the future to allow fractions.
As of 6/30/2014 all of the quizzes work except the one for Avogadro’s number.
