I just found something really useful - It balances equations

[Evan2468WDWA]

You can put the weight of a specific chemical into it and it will tell you all the other chemical weights needed to make it balance.
http://www.webqc.org/balance.php?reaction=SO2%2BAuCl3%2BH2O%3DSO3%2BHCl%2BAu

 

[dannlee]

And to get to the above...

http://www.webqc.org/balance.php?reaction=HNO3%2BHCl%2BAu%3DAuCl3%2BH2O%2BNO

 

[Evan2468WDWA]

Here is another online calculator I like. It can be used to convert most types of units.
http://www.convertunits.com/SI-units.php

 

[Wanwalai]

Thank you for all useful links :lol: