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### Topic: Would this weight ratio work?  (Read 10813 times)

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#### Questionguy

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« on: January 22, 2009, 07:28:01 PM »
In the laboratory, another method involves hydrolysis of PI3, the iodine equivalent of PBr3. In this method, I2 reacts with phosphorus to create phosphorus triiodide, which then reacts with water to form HI and phosphorous acid.

3 I2 + 2 P + 6 H2O = 2 PI3 + 6 H2O = 6 HI + 2 H3PO3

That's taken from wiki

I want to know if the follow weights would work according to that equation

7.3 grams totals weights

2 gram of iodine + 1.3 Gram of P + 4 grams of water (4mls of water) = 3.3 grams of PI3 + 4 given said of grams of H2O

1 part being 0.66 of a gram for the scale of weighing out the below formula, as I only have 2 grams of Iodine(I2). The other precursors aren't in shortage.

#### macman104

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« Reply #1 on: January 22, 2009, 08:06:12 PM »
You can't use weight ratios.  You need to convert your grams of iodine into moles, and then use molar ratios to find how many moles of each reactant you need, and then convert the moles back into grams.

#### Questionguy

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« Reply #2 on: January 22, 2009, 11:29:39 PM »
1 gram of Iodine has 0.007879943078443178 Iodine moles, double that to two grams and I get 0.015759886156886355 Iodine moles is what I got from googling a converter. Do you think you could help me out by explaining how the equation works relating to moles and ratios?

#### Borek ##### Re: Would this weight ratio work?
« Reply #3 on: January 23, 2009, 04:15:27 AM »
ChemBuddy chemical calculators - stoichiometry, pH, concentration, buffer preparation, titrations.info, pH-meter.info

#### Arkcon ##### Re: Would this weight ratio work?
« Reply #4 on: January 23, 2009, 06:43:49 AM »
1 gram of Iodine has 0.007879943078443178 Iodine moles,

Like Borek: said, you can't weigh anything out to 10 decimal places, so you can just chop them off, at a point where you can measure.  Or, you can just stop typing wherever.  It's all cool.

Quote
Do you think you could help me out by explaining how the equation works relating to moles and ratios?

Sure.  The units of a chemical formula are moles.  Nobody, (mostly*,) picks up 3 diatomic iodine molecules, goes to the shelf and takes 2 phosphorus atoms out of the jar, and stirs it together with the 6 molecules of water. What you want to do is start with the moles, from your reaction, and convert that to grams.  Gram you can measure, that is, to determine what you need for the reaction to go forward.

*Work continues in chemistry on the visualization and analysis of single trapped atoms, but that is far outside O.P.'s application.
Hey, I'm not judging.  I just like to shoot straight.  I'm a man of science.

#### Questionguy

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« Reply #5 on: January 23, 2009, 02:40:34 PM »
Ok, so I tried this

1 Iodine mole = 126.90447 grams

1 Phosphorus mole = 30.973761 grams

2 grams of Iodine = 0.015759886156886355 Iodine moles  (2 grams being all I have of Iodine)

1 gram of Phosphorus = 0.03228539149637011 P moles

1 gram of Iodine = 0.007879943078443178 I moles

3 I2 + 2 P + is all I'm focused on right now.

3 moles I2 = 380.71341 grams.

2 moles P = 61.947522 grams.

I then divide the above 380 by 61 and get 6 and by using the very top weights and the fraction of 1/6th I get from my 2 grams of Iodine, .3 grams of Phosphorus to balance the weight from the given moles I tried to balance, is this correct? Can anybody check this for me?

I'm using http://www.convertunits.com/from/moles+Phosphorus/to/grams
And http://www.convertunits.com/from/moles+Iodine/to/grams to convert
« Last Edit: January 23, 2009, 02:50:55 PM by Questionguy »

#### macman104

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« Reply #6 on: January 23, 2009, 06:15:19 PM »
I'm not entirely sure I followed what you did.  So I'll explain this way:

Calculate the number of moles of I2 in 2 grams.  Iodine does not exist as I, but I2.  Without a calculator, can you convert between moles and grams?  If not, here's a link to show you:

http://dbhs.wvusd.k12.ca.us/webdocs/Mole/Grams-to-Moles.html

Now you set up a ratio, 3 moles of I2: 2 moles of P = moles of I2 from above : x moles of P

Solve for x.  This is your moles of P that you need, then convert the moles to grams.

#### Questionguy

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« Reply #7 on: January 23, 2009, 06:49:19 PM »
I'm still confused could you do it for me?

#### macman104

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« Reply #8 on: January 23, 2009, 10:37:15 PM »
Let's go question by question:

What is the molecular weight of I2?
If you want to convert grams to moles, you divide __________ by ___________?  Read that link I gave you in my last post!!
Now use the above formula, and find how many moles of I2 are in 2 grams of Iodine!

Post the answer to each of those questions, and we'll go from there.

#### Questionguy

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« Reply #9 on: January 24, 2009, 01:21:03 PM »
2 grams of I2           0.0157598861 Iodine moles
-------------    =    --------------
126.90447 grams              1 mole

#### DrCMS

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« Reply #10 on: January 24, 2009, 01:28:33 PM »
Try again with macman104's 1st question

What is the molecular weight of I2?

#### Questionguy

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« Reply #11 on: January 24, 2009, 04:11:58 PM »
I give up, I've been toying with this s#*\$ for 2-3 days already, Thanks for the help guys

#### Questionguy

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« Reply #12 on: January 24, 2009, 10:08:31 PM »