Question #12530

1 Answer
Apr 10, 2017

The answer is c) 6.02 * 10^(24)

Explanation:

The idea here is that you must use the density of water to convert the given volume to grams

18 color(red)(cancel(color(black)("mL"))) * "1 g"/(1color(red)(cancel(color(black)("mL")))) = "18 g"

Now, the molar mass of water is approximately equal to "18 g mol"^(-1), which implies that 1 mole of water has a mass of "18 g".

You can thus say that your sample of water is equivalent to 1 mole of water. As you know, 1 mole of water must contain 6.02 * 10^(23) molecules of water -> this is known as Avogadro's constant.

You can thus say that your sample contains 6.02 * 10^(23) molecules of water.

To find the number of electrons present in the sample, calculate the number of electrons present in 1 molecule of water. To do that, grab a Periodic Table and look for the 8atomic numbers* of the two elements that make up the water molecule

"For H: " Z = 1

"For O: " Z = 8

As you know, a neutral atom has equal numbers of protons inside its nucleus and electrons surrounding its nucleus. This implies that 1 molecule of water will have a total of

"no of e"^(-)color(white)(.)"in 1 molecule" = overbrace(2 xx "1 e"^(-))^(color(blue)("from 2 atoms of H")) + overbrace(1 xx "8 e"^(-))^(color(purple)("from 1 atom of O")) = "10 e"^(-)

Therefore, the total number of electrons present in your sample will be equal to

6.02 * 10^(23) color(red)(cancel(color(black)("molecules H"_2"O"))) * "10 e"^(-)/(1color(red)(cancel(color(black)("molecule H"_2"O")))) = 6.02 * 10^(24) "e"^(-)