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### Topic: Ice Calorimetry question! Test tomorrow and very stuck:(  (Read 3376 times)

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#### flowerchild

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##### Ice Calorimetry question! Test tomorrow and very stuck:(
« on: March 05, 2010, 11:02:03 PM »
Hi there

I am very stuck with this question.
A 0.250 g piece of sodium metal is dropped into a mixture of 50.0 g of water (liquid) and 50.0 g of ice, both at 0 degrees celsius. The mixture is in a styrofoam container. The reaction is:

2 Na (s) + 2H20 (l) --> 2Na)H (aq) + H2 (g) delta H rxn = -368 KJ

The heat capacity of water and the resulting solution is 4.183 J/Kg. The enthalphy of fusion of ice is 333.4 J/g

a) How much heat is given off by the reaction of Na(s) with H20 (l)?

I'm guess that the answer is -368 KJ(2) = -736 KJ. Is this correct because there are 2 mol of Na reacting with water??

b) How much of the ice melts?

not sure for this question...i know heat of fusion = ice melted, but im not sure i understand the question

c) What is the final volume of the aqueous solution?

Im assuming it is 100 ml...

d) What is the final temperature of the aqueous solution?

no idea

e) after the reaction is complete, you add a drop of phenolphthalein indicator. What colour will the solution be?

I'm assuming pink?

Thanks for any *delete me*!!!

#### Borek

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##### Re: Ice Calorimetry question! Test tomorrow and very stuck:(
« Reply #1 on: March 06, 2010, 03:48:09 AM »
a) How much heat is given off by the reaction of Na(s) with H20 (l)?

I'm guess that the answer is -368 KJ(2) = -736 KJ. Is this correct because there are 2 mol of Na reacting with water??

0.0250 g is not 2 moles.

Quote
b) How much of the ice melts?

not sure for this question...i know heat of fusion = ice melted, but im not sure i understand the question

Whn sodium reacts heat is produced - that heat melts the ice.

Quote
c) What is the final volume of the aqueous solution?

Im assuming it is 100 ml...

No, it is sum of volumes of ice and water. That is, your answer would be (almost) correct if all ice melted, which is probably not the case.

Quote
d) What is the final temperature of the aqueous solution?

no idea

If not all ice melted, you have ice in water - there is only one temperature such mixture can have.

Quote
e) after the reaction is complete, you add a drop of phenolphthalein indicator. What colour will the solution be?

I'm assuming pink?

And that's the only correct answer... 1/5
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