Question

. Chromium 6, that is compounds/ions where chromium has a +6 chargeare known to be human...

. Chromium 6, that is compounds/ions where chromium has a +6 chargeare known to be human carcinogens. The legal limit for chromium 6 indrinking water is established as 10 ppb in California. If a glass of water(250 mL) contains 10 ppb chromium 6 how many chromium atoms arein the glass?

Homework Answers

Answer #1

ANS. 1 ppb is a unit of concentration and is defined as part per billion.

Formula is given as :

Concentration(ppb) = mass of solute(gm)/ mass of solvent * 109

Given that volume of water is 250mL.

Density of water is nearly 1gm/mL

So mass of 250mL = 250gm

We have to calculate mass of solute that is cromium ions.

So

10 = mass of solute/250gm * 109

MASS of solute = 10*250*10-9

= 2500 *10-9

= 2.5*10-6 gm

Atomic mass of chromium is 52.Charge does not affect the atomic mass of an element since neutrons and protons remain constant.So i will calculate for chromium only for convenience.

52 gm of chromium contains = 6.626*1023 atoms (avogadro number)

1 gm of chromium will contain = 6.626/52 *1023 atoms

2.5 *10-6gm of chromium will contain = 6.626/52 * 2.5 * 1017

= 0.318 *1017

= 3.2 *1016 atoms of chromium or chromium VI

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