Chemistry - October 2007

2007-10-19 21:12:33 · 3 answers · asked by ud_jeddah_83 1

The molar entropy of helium gas at 25°C and 1.00 atm is 126.1 J K-1 mol-1. Assuming ideal behavior, calculate the entropy of the following.

(a) 0.178 mol He(g) at 25°C and a volume of 4.61 L

(b) 2.37 mol He(g) at 25°C and a volume of 4219.3 L

2007-10-19 16:17:28 · 1 answers · asked by cuteeebabygirl 1

I was thinking of acid+copper+zinc=nigh everlasting electricty.
Is this true?

2007-10-19 15:51:41 · 5 answers · asked by taco 2

My teacher only ever gave us half life problems that worked out evenly and never bothered to teach us the formula or how it works. So now I some problems that I have to work out and I need to use the formula... please help! Here are the problems:

The first atomic explosion was detonated in the desert north of Alamogordo, New Mexico, on July 16, 1945. What percentage of the strontium-90 (t1/2 = 28.8 years) originally produced by that explosion still remained as of July 16, 2000?

A patient is administered 20 mg of iodine-131. How much of this isotope will remain in the body after 20 days if the half-life for iodine-131 is 8 days?

Thanks!

2007-10-19 15:28:14 · 2 answers · asked by Kai 2

Determine net ionic equations, if any, occuring when aqueous solutions of the following reactants are mixed.
Select "True" or "False" to indicate whether or not the stated reaction (or "no reaction") correctly corresponds to the expected observation in each case.


Sodium phosphate and potassium nitrate; No reaction occurs.

Magnesium chloride and sodium hydroxide; No reaction occurs.

Copper(II) sulfate and ammonium carbonate; No reaction occurs.

Sodium bromide and hydrochloric acid; Na+(aq) + Cl-(aq) --> NaCl(s)

Lead(II) nitrate and sodium chloride; No reaction occurs

2007-10-19 14:31:02 · 1 answers · asked by vivachappelle 2

2007-10-19 14:10:26 · 4 answers · asked by Anonymous

2007-10-19 14:08:31 · 2 answers · asked by tmb82 2

water is an excellent conducter of heat?
the inside of the paper is wet?
paper is a poor conducter of heat?
the paper cup cannot become appreciably hotter than the water it contains.

2007-10-19 12:54:59 · 9 answers · asked by Anonymous

The seven most abundant ions in seawater make up more than 99% by mass of the dissolved compounds. They are listed in units of mg ion/kg sea water: chloride 18,900; sodium 10,560; sulfate 2650; magnesium 1270; calcium 400; potassium 380; hydrogen carbonate 140.
(a) What is the mass % of each ion in seawater.
(b) What percent of the total mass of ions is sodium ion
(c) How does the total mass % of alkaline earth metals compare with the total mass % of alkali metal ions
(d) Which makes up the larger mass fraction of dissolved components, anions, and cations?

Could you just show me a quick set up please?
Also, what are the anions, and cations? (heard the terms last year)

Thanks a bunch!!

2007-10-19 11:57:23 · 2 answers · asked by Anonymous

2007-10-19 11:29:42 · 3 answers · asked by simranjit chera 1

Which of the following designations, polar or nonpolar, are correct for the given compounds below ?
a) HBr : polar
b) CF4 : polar
c) CH3CH2CH2OH : nonpolar
d) I3- : polar

There can be more than one answer.

2007-10-19 10:31:08 · 3 answers · asked by Anonymous

Anhydrous sodium carbonate was added to aspirin. I have the equation for this right I think, the R-COOH (of aspirin) --->R-COONa and H2O and CO2 are formed.
Then dilute HCl is added and effervescence is observed. What is the reaction occurring in this part?
Thanks

2007-10-19 10:28:05 · 2 answers · asked by lalala123 1

i'm stuck on a chem problem that i have been looking at for about 30 min. If anyone can help that would be greatly appreciated!(Please explain why too!)

Identify the hybridization of the carbon atom(s) in CO3-2

Also give the number of π bonds in the molecule or ion

2007-10-19 10:26:56 · 2 answers · asked by Anonymous

Which of the following compounds have a nonzero dipole moment?
a) SiBrH3 b) NH4+ c) GaH3 d) H2

must enter all tru statements

2007-10-19 10:22:02 · 3 answers · asked by physicsisgay 2

I saw this video on myspace videos and it had a person filling up a glass of water, then putting 2 batteries in the water for 40 minutes. He then lit a match to it and the water ignited.

Is this true or did he fake it?

2007-10-19 10:21:29 · 7 answers · asked by Chris Stewart 5

1) The energy of the electron in the lowest level of the hydrogen atom (n=1) is -2.179×10-18 J.
What is the energy of the electron in level n=5?

2) The electron in a hydrogen atom moves from level n=1 to level n=2. (a) Is a photon emitted or absorbed? (b) What is the wavelength of the photon?

3) An excited hydrogen atom emits a photon with a wavelength of 486.2 nm. (a) In what region of the spectrum is this photon? (b) What is the frequency of this photon?

4 A hydrogen atom in the ground state absorbs a photon of wavelength 97.2 nm. (a) What energy level does the electron reach? (b) This excited atom then emits a photon of wavelength 486.2 nm. What energy level does the electron fall to?

2007-10-19 10:16:55 · 3 answers · asked by KC 1

Platinol is an anticancer drug with molecular formula Pt(NH3)2Cl2. Platinum is a precious metal, and the cost of making platinol is determined by the cost of the platinum, which is $19.00 per gram. One dose of the drug contains 11.9 mg of platinol. How many doses of platinol could be produced for 71.8 dollars?

2007-10-19 09:51:04 · 2 answers · asked by cory c 1

I would like to melt down old necklaces, coins, jewlery and just have bars of precious metals if it is possible. Anyone know how to do this

2007-10-19 09:50:25 · 1 answers · asked by davetemp60067 1

Does anyone know how can I synthesis cyclopentane from molecules that doesn't have more than two carbon atoms?
Thanx for your help!

2007-10-19 09:35:49 · 2 answers · asked by Andreja K 3

How do you make fog come out like over liquid like this,
http://www.handbook.unsw.edu.au/images/userimages/SCI/ChemistryI.jpg
without all the funky chemicals?

2007-10-19 09:19:14 · 4 answers · asked by Mr.AwEsOmE555 1

Diamagnetic is defined as atoms or ions in which all the electrons are paired in filled shells so their magnetic fields effectively cancel each other. Now, I know N2 is diamagnetic because it was the answer to a question on a practice test that I took but O2 was also a choice and it seems to me that there are no unpaired electrons when oxygen is bonded to itself through a double bond. Am I wrong about this? Why is oxygen not diamagnetic?

2007-10-19 09:13:20 · 1 answers · asked by Anonymous

How do you know whether an element's atom type is an isotope, ion, or neutral atom?

For instance, if Al (Aluminum) has the following properties, is it an isotope, ion, or neutral?:
Atomic #: 13
Mass #: 27
Protons: 13
Neutrons: 14
Electrons: 13

2007-10-19 08:20:41 · 5 answers · asked by Anonymous

how do i find the OH?

2007-10-19 07:50:51 · 4 answers · asked by Dirty S 1

a) Sodium and cesium
b) Potassium and bromine

2007-10-19 07:44:56 · 3 answers · asked by Kristyn 1

Why are some elements more reactive than others?

2007-10-19 07:41:28 · 3 answers · asked by Kristyn 1

An electron has a de Broglie wavelength of 240nm, What is the speed of the electron? I dont get how to do this sompel please help.

2007-10-19 07:10:54 · 2 answers · asked by Cannot Think of Name 2

A 10.0-g sample of a mixture of CH4 and C2H4 reacts with oxygen at 25.0oC and 1.00 atm to produce CO2(g) and H2O(l). If the reaction produces 545 kJ of heat, what is the mass percentage of CH4 in the mixture?

I would appreciate any help, I have tried this so many times...

2007-10-19 07:07:00 · 4 answers · asked by Anonymous

2007-10-19 07:05:52 · 6 answers · asked by Anonymous

1) A infrared photon has a frequency of 9,469 GHz. What is its wavelength in centimeters (cm)?

2) Which of the following transitions of a single electron would require the absorption of a photon of light with the shortest wavelength?
Answer choices:
a) n = 3 to n = 2
b) n = 1 to n = 4
c) n = 2 to n = 4
d) n = 5 to n = 1
e) n = 3 to n = 5

3) Which is not a possible ml value for an orbital that has the following:
n = 6, l = 2
Ans choices:
a) -1
b) +1
c) -2
d) -3

2007-10-19 06:59:35 · 1 answers · asked by hey there! 1

a lot of swords nowadays are being made out of stainless steel and high carbon steel, but what would be an extremely tough metal to make a sword out of so it would be tough enough to slice through concrete, trees, and metal without marring the blade?

2007-10-19 06:58:53 · 5 answers · asked by Jonny Mick 2