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Topic: SOS Chem test!!  (Read 7742 times)

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Offline RydbergConstant

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SOS Chem test!!
« on: October 19, 2007, 02:36:32 AM »
I'm doing a practice test to review for a major test tomorrow and I need help on the following problems por favor! We're learning about concentration, dilution, molarity, thermochemistry, electromagnetic spectrum, quantum numbers, and anything else i've forgotten in that general range.

A 5.00 sample of sodium chloride was dissolved in water to form 250. mL of solution. What is the molar concentration of the solution?

Answer: 0.342 M

Which of the following photons carries the SMALLEST amount of energy?
a)a photon with the wavelegnth of 656 nm
b) a photon with the frequency of 1.4E14 s^-1
c) a photon of UV light
d) a photon of yellow light
e) a photon with the energy of 2.04E-18 J

Answer: B


Thanks!!

Offline Borek

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Re: SOS Chem test!!
« Reply #1 on: October 19, 2007, 03:13:51 AM »
Assuming you meant 5.00 g answer to 1st question is OK.
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Offline RydbergConstant

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Re: SOS Chem test!!
« Reply #2 on: October 19, 2007, 03:27:44 AM »
Yea I was trying to figure out if my professor had mistyped it because it made no sense at all. At first I thought it was 5.00 mol, but I worked it out with grams like you said and it makes sense! So you know how to work out the second problem??

Offline Sev

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Re: SOS Chem test!!
« Reply #3 on: October 19, 2007, 03:46:23 AM »
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So you know how to work out the second problem??

Use the fact that E = hf = hc/lambda.

Offline RydbergConstant

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Re: SOS Chem test!!
« Reply #4 on: October 19, 2007, 03:48:44 AM »
Ahh!! Actually what about this problem:


Acids and bases undergo a neutralization reaction in which a salt and water are formed. What is the molar concentration(molarity) of the hydrochloric acid solution, if 36.0 mL of it requires 18.9 mL of 0.213 M of the calcium hydroxide solution to get neutralized:

Ca(OH)2(aq) + 2HCl(aq) --> CaCl2(aq) + 2H2O(l)

Answer: 0.224 M


What equation do I use for this??

Offline RydbergConstant

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Re: SOS Chem test!!
« Reply #5 on: October 19, 2007, 03:49:49 AM »
Quote
So you know how to work out the second problem??

Use the fact that E = hf = hc/lambda.


Thank you!

Offline Sev

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Re: SOS Chem test!!
« Reply #6 on: October 19, 2007, 04:03:53 AM »
Quote
Acids and bases undergo a neutralization reaction in which a salt and water are formed. What is the molar concentration(molarity) of the hydrochloric acid solution, if 36.0 mL of it requires 18.9 mL of 0.213 M of the calcium hydroxide solution to get neutralized:

Ca(OH)2(aq) + 2HCl(aq) --> CaCl2(aq) + 2H2O(l)

Answer: 0.224 M


What equation do I use for this??

n=cv
Find moles of Calcium hydroxide.  How many moles of HCl are needed to neutralise this?


Offline RydbergConstant

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Re: SOS Chem test!!
« Reply #7 on: October 19, 2007, 04:08:06 AM »
Quote
Acids and bases undergo a neutralization reaction in which a salt and water are formed. What is the molar concentration(molarity) of the hydrochloric acid solution, if 36.0 mL of it requires 18.9 mL of 0.213 M of the calcium hydroxide solution to get neutralized:

Ca(OH)2(aq) + 2HCl(aq) --> CaCl2(aq) + 2H2O(l)

Answer: 0.224 M


What equation do I use for this??

n=cv
Find moles of Calcium hydroxide.  How many moles of HCl are needed to neutralise this?



It doesn't say how many moles of HCl are needed to neutralize it

Offline Sev

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Re: SOS Chem test!!
« Reply #8 on: October 19, 2007, 04:13:46 AM »
Quote
Quote
Acids and bases undergo a neutralization reaction in which a salt and water are formed. What is the molar concentration(molarity) of the hydrochloric acid solution, if 36.0 mL of it requires 18.9 mL of 0.213 M of the calcium hydroxide solution to get neutralized:

Ca(OH)2(aq) + 2HCl(aq) --> CaCl2(aq) + 2H2O(l)

Answer: 0.224 M


What equation do I use for this??

n=cv
Find moles of Calcium hydroxide.  How many moles of HCl are needed to neutralise this?



It doesn't say how many moles of HCl are needed to neutralize it

It does.  Your rxn eqn gives you this info.  It will be twice number of mole of Ca(OH)2.

Offline RydbergConstant

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Re: SOS Chem test!!
« Reply #9 on: October 19, 2007, 04:22:16 AM »
I get it now! Thanks!! You were a major help

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