Question

Water has a mass per mole of 18.0 g/mol, and each water molecule (H2O) has 10 electrons. (a) How many electrons are there in 2.82 liters of water? (1 liter is equivalent to 1.00 × 10-3 m3) (b) What is the net charge of all these electrons?

Answer 1

A) Need to know besides whats given: Avogadro's number (6.022x10^23 molecules/mole) and density of water (1.00x10^3 kg/m^3) and convert kg to g so everything cancels:

2.82 L x (1.00x10^-3)m^3/L x (1.00x 10^6)g/m^3 x (1/18) mol/g x (6.022 x 10^23) molecules/mol x (10) electrons/molecule = (9.434x10^26)electrons!

B) q= ?C q=Ne (e=1.602x10^-19)

q= (9.434x10^26) x (1.602x10^-19)= - 1.51x10^8C

Don't forget to add your - sign because you are talking about electrons!