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Topic: Stoichiometry Problem  (Read 6261 times)

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BleedGreenTea

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Stoichiometry Problem
« on: June 08, 2005, 06:56:39 PM »
Hello, my final is coming up and I can't remember how to do this.

How many grams of sodium hydroxide are produced by the reaction of 45.0 grams of sodium with water?

My work:
45.0 g Na * (1mol / 22.99g Na) * (1mol NaOH / 1 mol Na) * (39.99g / 1 mol NaOH)

= 78.3 g NaOH

Now, How many liters of hydrogen are produced?. I don't know what to do.
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arnyk

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Re:Stoichiometry Problem
« Reply #1 on: June 08, 2005, 07:08:02 PM »
That looks good so far -- first I would write out the chemical reaction.  Use the molar ratios to determine the moles of H2(g).  As for the volume of hydrogen produced, unless they give you the conditions (like STP/SATP) I don't know how you would calculate volume using just the moles.  Granted, I'm not that advanced myself so there may be a better way.
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Offline DrCMS

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Re:Stoichiometry Problem
« Reply #2 on: June 09, 2005, 03:56:52 AM »
At room temperature 1 mole of gas is about 24 litres as a rough rule of thumb.

So calculate how many moles of hydrogen are produced and muliply by 24.

Show that in your workings and state that assumption.  

Alternatively use PV = nRT and pick a temperature and pressure say 25°C and 1 atms and state that in the workings.
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Offline Borek

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Re:Stoichiometry Problem
« Reply #3 on: June 09, 2005, 04:51:01 AM »
Quote from: DrCMS on June 09, 2005, 03:56:52 AM
At room temperature 1 mole of gas is about 24 litres as a rough rule of thumb.

In general you are right, but most teachers tend to expect calculations done for 22.4L as if every reaction was done at 0 deg C. No idea why ;)
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Offline xiankai

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Re:Stoichiometry Problem
« Reply #4 on: June 09, 2005, 06:16:32 AM »
shouldnt it be 24.5 L then?
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arnyk

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Re:Stoichiometry Problem
« Reply #5 on: June 09, 2005, 05:59:10 PM »
They don't tell you the conditions though.  At STP the molar volume would be 22.4 mol/L and at SATP it would be 24.8 mol/L.  So I guess if you were to 'assume' room temperature then you'd go with SATP.
« Last Edit: June 09, 2005, 05:59:56 PM by arnyk »
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Offline Donaldson Tan

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Re:Stoichiometry Problem
« Reply #6 on: June 11, 2005, 08:41:37 AM »
include the words "assuming RTP condition" in your answer
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