What is the molarity of a 5ml solution containing 0.7 micrograms of selenium?

Answer 1

The answer is

1.77 * 10-6 M.

Solution:

.7 ug * (1 g \ 106 ug) This converts our value from micrograms (ug) to grams (g).

* (1 mole Selenium \ 78.96 g Selenium) This gives out our # of moles Selenium by using Selenium's molar mass (78.96 g/mol).

= 8.87 * 10-9 moles Selenium

Divided by the volume in liters (.005 L)

= 1.77 * 10-6 moles Selenium \ 1 L (M)

Check:

.005 L * (1.77 * 10-6 moles Selenium\ 1 L)

= .00000177 moles Selenium

* (78.96 g Selenium \ 1 mole Selenium)

* (106 ug \ 1 g)

~= .7 ug.

- Mike

Answer 2

To calculate the molarity, you need the molecular weight of selenium. Selenium's atomic weight is 78.971 g/mol. First, convert 0.7 µg to grams (0.0000007 g). Then, calculate the number of moles (0.0000007 g / 78.971 g/mol). Finally, determine the molarity by dividing the moles by the volume in liters (5 ml = 0.005 L).