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Chemistry Forums for Students => High School Chemistry Forum => Topic started by: xstellarx on December 29, 2007, 02:23:53 PM

Title: chemistry scavenger hunt!! H E L P!
Post by: xstellarx on December 29, 2007, 02:23:53 PM
hi. i have a 25 item scavenger hunt for chemistry. i found most of the items accept a few. it would be great if you guys could help me out. thanks!!

3. the mass of sodium chloride that would be produced when 2.3 g of sodium reacts with .56 L of chlrine gas. Assume STP and 100% yield. Calculations and balanced equation required.

16. a hydrocarbon with molecular weight > 100. common name, chemical name, chemical formula.

18. an amount of water whose temperature would change 15 degrees C when it absorbed 630 calories of  heat energy. calculations required  (am i using a formula with vaporization? or something along those lines)


Title: Re: chemistry scavenger hunt!! *delete me*
Post by: Sev on December 30, 2007, 10:48:57 PM
Quote
3. the mass of sodium chloride that would be produced when 2.3 g of sodium reacts with .56 L of chlrine gas. Assume STP and 100% yield.

Start with balanced eqn - then consider limiting reagents
Title: Re: chemistry scavenger hunt!! *delete me*
Post by: IITian on December 31, 2007, 11:37:19 AM
Paper chromatography is an analytical technique (however, not used that often these days) for separating and identifying mixtures that are often coloured, especially pigments. The solvent front carries the solutes depending on their molecular weights. Thus, lighter material is carried further as opposed to heavier fractions

Title: Re: chemistry scavenger hunt!! *delete me*
Post by: xstellarx on December 31, 2007, 04:54:52 PM
Quote from: Sev on December 30, 2007, 10:48:57 PM
Quote
3. the mass of sodium chloride that would be produced when 2.3 g of sodium reacts with .56 L of chlrine gas. Assume STP and 100% yield.

Start with balanced eqn - then consider limiting reagents







we havent learned how to balance equations yet.. ive looked it up in my textbook and review but its so confusing. i cant quite understand it
Title: Re: chemistry scavenger hunt!! H E L P!
Post by: Sev on December 31, 2007, 06:47:53 PM
1. So called skeletal equation is: Na + Cl2 → NaCl.  Note Cl is not balanced.
2Na + Cl2 → 2NaCl - Now it is balanced  :)

You need to work out how many moles of Na and Cl2 you have (for Cl2 this will involve using gas law).
Title: Re: chemistry scavenger hunt!! H E L P!
Post by: xstellarx on January 01, 2008, 02:24:33 PM
ok so to figure out a mole of something i would do a ratio right? i learned about moles in september so its kinda fuzzy lol. n then after i convert them what do i do next?
Title: Re: chemistry scavenger hunt!! H E L P!
Post by: Sev on January 01, 2008, 07:44:22 PM
mNa = 2.3g.  MNa(molar mass) = 22.99gmol-1 - so you have 2.3/22.99 = 0.1mol

At STP 0.56L Cl2 is 0.0246mol.

2Na + Cl2 → 2NaCl

Cl2 is the limiting reagent...looking at numbers only ~half of Na will react.  Now use ratios.  If 1 mol Cl2 gives 2 mol NaCl (as shown in rxn eqn), how many will 0.0246 mol give?
Title: Re: chemistry scavenger hunt!! H E L P!
Post by: Alpha-Omega on January 01, 2008, 08:45:54 PM
HINT:  The formula for you hydrocarbon =  100g is C7H16  from the CnH2n + 2 ruleor C(7) + H2(7) + 2 = C7H16
7(12) = 84
16(1) = 16
84 + 16 = 100

Now figure out the structure and the name
Title: Re: chemistry scavenger hunt!! H E L P!
Post by: Alpha-Omega on January 01, 2008, 08:59:46 PM
MY BAD...question states hydrocarbon greater than 100....tht is easier...

CnH2n+2  is even easier....just use C8H18...and that is an easy one let me knw what name and weight you get.

Think I need a break making mistakes now....LOL
Title: Re: chemistry scavenger hunt!! H E L P!
Post by: yosh on January 02, 2008, 12:30:11 AM
For 18. just use the equation Q=MC(delta T)
Title: Re: chemistry scavenger hunt!! H E L P!
Post by: Alpha-Omega on January 02, 2008, 12:40:25 AM
Yes you sure are and you are solving for m.  You can check your answer in this calculator:  http://hyperphysics.phy-astr.gsu.edu/hbase/thermo/spht.html