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3 The human body contains around 0.025 g of iodine molecules, I2. Which of the
following shows the number of iodine atoms in 0.025 g of I2?
The Avogadro constant is 6.02 × 1023 mol–1.
A 0 025
---------
126 9 x. 6 02 1023
.
× . ×
B 0 025
---------
253 8 x. 6 02 1023
.
× . ×
C 253 8
-----------
0 025 x. 6 02 1023
.
× . ×
D 126 9
-------
0 025 x6 02 1023

The answer is A but im not sure why because i thought it was B. i thought it was B because if its Iodine, and its I2, surely you do 126.9 x 2? :| Help.

Original post by EffKayy

3 The human body contains around 0.025 g of iodine molecules, I2. Which of the
following shows the number of iodine atoms in 0.025 g of I2?
The Avogadro constant is 6.02 × 1023 mol–1.
A 0 025
---------
126 9 x. 6 02 1023
.
× . ×
B 0 025
---------
253 8 x. 6 02 1023
.
× . ×
C 253 8
-----------
0 025 x. 6 02 1023
.
× . ×
D 126 9
-------
0 025 x6 02 1023

The answer is A but im not sure why because i thought it was B. i thought it was B because if its Iodine, and its I2, surely you do 126.9 x 2? :| Help.

yeah, but the question asks you for iodine ATOMS

Reply 2

Maker

20

I think you are getting mass and volume mixed up. The number of atoms in 126.9g of iodine is 6.02 x 1023.

The number of atoms in 0.025g is 0.025/126.9 x 6.02 x 1023

Molecular mass is only relevant when its a gas and you are using its volume to determine number of moles or molecular weight.

Reply 3

azrah vakil

3

Original post by Maker

I think you are getting mass and volume mixed up. The number of atoms in 126.9g of iodine is 6.02 x 1023.

The number of atoms in 0.025g is 0.025/126.9 x 6.02 x 1023

Molecular mass is only relevant when its a gas and you are using its volume to determine number of moles or molecular weight.

sorry but i didnt understand
can u explain this again!

Reply 4

bleak_rage

11

Hi!

If you think a bit, you'll realize that the mass of iodine molecules is the same as the mass of iodine atoms. Since they are asking for number of atoms you're answer should be A, i.e. moles of iodine atoms x Avogradro constant.

Hope it helped!

Reply 5

username3110466

12

Im sure he needed the help 7 years later.....

Reply 6

bleak_rage

11

Original post by theoneandonlybob

Im sure he needed the help 7 years later.....

LOL just realized this post was 7 years old...

Reply 7

SAEYINA

8

Maybe this a very late to reply, but after asking my lecturer, the following working is like these:I2 = 2 x I atoms , Molar mass = 2(126.9 g mol -1 )No. of Atoms = 2 x (0.025 / 2 x 126.9) x 6.02 x 10^23 = 0.025/126.9 x 6.02 x 10^23 So yeah, the answer is A.

Reply 8

Pigster

20

Original post by SAEYINA

Maybe this a very late to reply, but after asking my lecturer, the following working is like these:I2 = 2 x I atoms , Molar mass = 2(126.9 g mol -1 )No. of Atoms = 2 x (0.025 / 2 x 126.9) x 6.02 x 10^23 = 0.025/126.9 x 6.02 x 10^23 So yeah, the answer is A.

Welcome to TSR and yes, you're right: there is little point finding such an old thread and replying to it. The OP will have finished university long ago and is highly unlikely to still visit here and I'm pretty sure no longer cares about how many atoms there are in 0.025 g of iodine.

Reply 9

SudiT

10

Original post by SAEYINA

Maybe this a very late to reply, but after asking my lecturer, the following working is like these:I2 = 2 x I atoms , Molar mass = 2(126.9 g mol -1 )No. of Atoms = 2 x (0.025 / 2 x 126.9) x 6.02 x 10^23 = 0.025/126.9 x 6.02 x 10^23 So yeah, the answer is A.

9 years later and I am struggling with the same question but that makes sense, thank you!

Reply 10

Murad Osman

2

I just want to keep this thread going

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