1

New Theories / Does Earth/Moon Model Show Cavendish Is Wrong?

« on: 26/09/2008 14:13:50 »

But how are you accomplishing that scale-down?  You should realize that the size of the earth and moon vary as the cube of their radii.  Meaning  that if you make the earth one millionth its normal size, the mass decreases by a factor of 10¹⁸.  Doing the same to the moon results in a similar effect.  So, while the distance between the moon and the earth has decreased by a factor of 10⁶, the force due to gravity has decreased by a factor of 10³⁶.  That's 1,000,000,000,000,000,000,000,000,000,000 times the change of the distance. 

Is it really any surprise that you might not see an effect?

2

Chemistry / What happens to ice when it can't expand?

« on: 24/09/2008 15:36:28 »

Actually, at a low enough temperature (below about -20 °C or -4 °F) it WILL freeze at normal or higher pressures.  Of course, if the pressure is low enough, you have the issue of the water preferring to be gaseous.

The freezing point of water stays roughly the same over a fairly broad pressure range.  Keep in mind that it takes roughly 2000 bar (that's 2000x normal atmospheric pressure) to lower the freezing point by 20 °C (36°F).  That's roughly 100 bar per °C.

3

Chemistry / Chemistry classes?

« on: 24/09/2008 15:29:59 »

As I mentioned, physical is a lot like general chemistry, but you go more in depth into the topics.  Physical chemistry is, as implied, a mix of physics and chemistry, and studies the forces and properties associated with matter.  To give a few examples of topics:
thermodynamics
kinetics
quantum mechanics
electrochemistry
atomic structure

Since you've taken general chemistry, you should recognize these topics.  In general chemistry, the coverage of the topics is rather superficial.  In p-chem, you dig deeper into these topics, which requires more math (meaning calculus, at least).  In my opinion, this was the most difficult of the chemistry courses that I took, but it was also one of the most intellectually rewarding.  I liked it so much I took three semesters of it, although I eventually went into the field of inorganic chemistry.

Just as physics and chemistry can combine into physical chemistry (or chemical physics), you can also combine physical chemistry with other chemical fields, to get things like physical organic chemistry, physical inorganic chemistry or bio-physical chemistry to name a few.

Dick

4

Physics, Astronomy & Cosmology / Why is the moon moving further away from the Earth?

« on: 23/09/2008 19:53:39 »

                    WHY IS THE MOON NOT SPINNING THEN??  []

The moon IS spinning, at a rate of approximately one rotation per month.

5

Chemistry / What determines the numbers of protons and neutrons in an atom?

« on: 22/09/2008 20:40:14 »

Thanks for the responses. We got John Law's question answered. I haven't figured out why some questions which I regard as silly and non-scientific get substanial responses while to-the-point scientific questions end up in limbo. (Actually I have figured it out, but I don't like the answer.)

So what's the answer?

6

Chemistry / What determines the numbers of protons and neutrons in an atom?

« on: 22/09/2008 19:55:27 »

I honestly don't know that much about nuclear physics/nuclear chemistry.  I kind of look at neutrons as being a buffer needed to shield the positive charges of the protons from each other. 

Hydrogen, with only one proton, doesn't need this buffer, so it's hard to find any atoms with any neutrons at all.  As soon as you add a second proton (helium), you need to add that buffer, so neutrons are necessary.  I know that there are certain "magic numbers" with respect to proton and neutron count, but I have no knowledge of the basis of those numbers.

I see most of chemistry arising from the number of electrons present, so I tend to look at all chemical problems from this point of view.  Of course, the number of electrons is intimately dependent on the number of protons, which is why we tend to organize the periodic table by atomic number.

I didn't focus much on neutrons because it didn't appear to have anything to do with the original question.

Dick

7

Chemistry / Chemistry classes?

« on: 22/09/2008 19:45:11 »

Dr. Dick , OMG chemistry easy?  I guess you're a born scientist!  Is that I heard some time ago that chemistry is hard at first, but then it's a piece of cake.  Hope so because Im making my last years of career working in a pharmaceutical company.  Hopefully, I'm just fulfilling my mid-life crisis.  9 years ago I decided to study science since I enjoyed them so much in school.  Just wanted a change in my boring life, something challenging.  I guess I found it. How many years of your life this you study?

I would definitely say that general chemistry (1st year in the states) is not the hardest class in the chemistry curriculum. 

Some people think organic is easier, some think it's harder.  It's just very different.

Physical chemistry is definitely harder.  General chemistry is kind of like P-chem lite. 

I didn't think inorganic chemistry was too bad, but descriptive inorganic is a lot of memorization (more so than organic).

How many years of schooling?  All-in-all, 11 years since high school, but I sometimes don't count my two years at Caltech, since I didn't get a degree from there.  I left to get a job, instead, then returned to grad school several years later for a second try.  Normally, it's 4 years for the bachelor's + 5 years for the Ph.D., although that can vary a bit from person to person.

8

Chemistry / adressing two issues (fresh water and energy)

« on: 22/09/2008 19:37:58 »

You couldn't generate any net energy, since it takes a significant amount of energy to do this.

Dick

9

Chemistry / What happens to ice when it can't expand?

« on: 22/09/2008 19:36:32 »

Dry ice temperatures would certainly be enough to freeze the water.

In this instance, the freezing point would change.  As the temperatures cools from 4 °C, the water will try to expand.  Since it can't, the pressure will increase.  Higher pressures require lower temperatures to freeze water, but the difference in temperature is pretty small.  The absolute lowest that the freezing point can go is approximately -20 °C, which is the liquid/Ice(I)/Ice(III) triple point temperature, at a little over 2000 bar(1).  I don't know what pressure would ultimately be achieved, but if you go over that triple point pressure, the freezing point starts rising again.

Dick

(1) Greenwood & Earnshaw, Chemistry of the Elements, 2nd ed., p. 624.

10

Chemistry / Re: How do hydrogen and oxygen react to make water?

« on: 20/09/2008 03:56:32 »

The process you're talking about is not electrolysis, though.  Electrolysis is the process of using electricity to cause a non-spontaneous reaction to occur.  The reaction between H2 and O2 is spontaneous, and would lead to a voltaic (aka galvanic) cell, or a fuel cell, depending on the setup.

You could also use an inert metal (such as platinum) for your electrodes.

And I think the temperature of the boom would be high enough to ensure the water stayed gaseous.  

11

Chemistry / What determines the numbers of protons and neutrons in an atom?

« on: 20/09/2008 03:49:40 »

The charge is a whole number because we say it is.  The +1, -2, or whatever refers to the polarity and the number of net electronic charges present.  Charge is actually measured in coulombs, and an electron or proton has a charge of -/+ 1.60 x 10^-19 coulombs.  This is the smallest increment of charge that we can measure (supposedly the smallest increment that exists, but who knows what subatomic particles we may discover in the future).  If the charge is +3.20 x 10^-19, then we say the ion has a charge of +2.

As far as the atom "keeping track", it's actually quite simple.  It doesn't.  Electrons can adhere to an existing atom, creating an anion.  They can leave an existing atom, creating a cation.  The tendency towards this happening depends on electrostatics.  As an electron approaches an atom, it can feel repulsions caused by the electrons already present, and attractions caused by the protons present. 

If the attractive forces are stronger, as tends to be the case with the nonmetals (they're smaller, so the electron can get closer to the nucleus), the electron will adhere to the atom.  If the repulsive forces are stronger, the electron will tend to veer away.

Sometimes, an atom with strong attractive forces approaches an atom with weak attractive forces.  When this occurs, an electron will leave the weakly attractive atom and hop over to the strongly attractive atom.

Now, to comment on something that stevewillie said, most elements do not have an equal number of protons and neutrons.  That's really only partially true, even for elements from helium to calcium (less than a quarter of the stable elements).  After that (and even some elements before that), the atoms prefer to have more neutrons than protons.  By the time you get to bismuth (the last element with a stable isotope), the ratio of neutrons to protons is about 1.5 : 1.

12

Chemistry / Chemistry classes?

« on: 19/09/2008 15:15:11 »

I would like to know from all the chemist here, if the first class of chemistry the hardest or not?
somebody told me that the first & second chemistry classes were the hardest from all of the B.S. degree.  Is this true?
I would appreciate your answer and /or opinion on this.

Let me see if I understand your question, first.  Are you asking if the first year of a chemistry degree is harder than the first year of other degrees?  If so, I suppose that depends on the person.  Personally, I found the first year of chemistry pretty easy (I have a B.S. and Ph.D. in chemistry).  I found my humanities classes more difficult.

Dick

13

Chemistry / What are calories?

« on: 19/09/2008 14:56:55 »

the amount of energy required to raise 1 g of water to 1º Celsius

Sorry to be the pedant, but the calorie is
the amount of energy required to raise 1 g of water by 1º Celsius

To be even more pedantic, it's the amount of heat required to raise the temperature of 1 g of water from 14.5 °C to 15.5°C.  (The specific heat of water changes with temperature).

Dick

14

Chemistry / Alcohol Cooks Eggs ?....now c'mon ?.....really ?

« on: 23/01/2008 18:29:43 »

Technically, cooking does involve heat, so you wouldn't actually be cooking the eggs.  However, the process of cooking the egg results in denaturation of the proteins present.  Mixing them with alcohol could have the same effect, but I've never seen it done.
Denaturation is a process whereby the 3-d structure of the protein is changed.  Since this structure is dependent on the environment, adding a lot of alcohol where there's normally water would have the effect of changing this 3-d structure.  However, there's no guarantee that the change would be the same that you would see upon heating.

Sounds like a kitchen science experiment to me.  []

Dick

15

Chemistry / Calories ...what are they all about ?

« on: 23/01/2008 18:23:45 »

You can get a rough idea of the Calories contained in food with the following calculation:

  9.0 x (g of fat)             {each gram of fat contains about 9 Calories}
+ 4.0 x (g of carbohydrate)    {each gram of carbo contains about 4 Calories}
+ 4.0 x (g of protein)         {each gram of protein contains about 4 Calories}
------------------------
total Calories

As pointed out earlier, however, cellulose (technically, a carbohydrate) isn't converted to energy in the body, so "fiber" shouldn't be counted (I think it sometimes is, however).

Dick

16

Chemistry / Hybridization Help!

« on: 23/01/2008 18:13:55 »

It's actually pretty easy to calculate the hybridization of an atom.  Count the number of things (either atoms, lone pairs or unpaired electrons).  This will tell you the number of atomic orbitals that go into making the hybrid orbitals.

1 thing = irrelevant - not hybridized
2 things = 2 orbitals - s + p = sp-hybridized (e.g., C in CO2)
3 things = 3 orbitals - s + p + p = sp²-hybridized (e.g., C in C2H4, S in SO2)
4 things = 4 orbitals - s + p + p + p = sp³-hybridized (e.g., CH4, NH3, H2O)

It is my not-so-humble opinion that hybridization is a useful fiction espoused by organic chemists to explain the very small portion of the periodic table in which they are interested.  Hybridization and VSEPR theory tend to fall apart unless you're dealing with a specific set of circumstances that are almost always present in organic molecules, but are often not present in inorganic molecules.

17

Chemistry / Dilute acids

« on: 23/01/2008 17:54:26 »

Most hardware stores will carry some concentrated acids, such as hydrochloric (aka muriatic) acid or sulfuric acid.  Then you can dilute it yourself, as Wally mentioned.

Dick

18

Chemistry / What’s in your shampoo?

« on: 11/12/2007 18:40:28 »

By the way, was your shampoo a "conditioning shampoo"?

No, not specifically.
Thanks also for adding more specifics. The SLS/SLES concern me specifically as I’m finding that more and more people develop sensitivities to these. There are very few shampoos currently available without SLS/SLES and I’m still trying to find out why that is so and what alternatives there are.
I’ve found Sodium Coco-Sulfate mentioned but am still doing more research. Any help / pointers are most appreciated.

There's essentially no difference between sodium lauryl sulfate (SLS) and sodium cocosulfate (except for the name, of course). 

Technically, "lauryl" refers to a 12-carbon chain, but in the industry, this just means that the average chain length is approximately 12 carbons.  It's actually a mixture of materials (e.g., 8 C, 10 C, 12 C, 14 C, etc.).  When they get a weighted average, it might be, say, 12.1 carbons.  That makes it "lauryl".  The root "coco" means it comes from coconut oil, which just happens to have an average chain length of about 12 C.

Dick

19

Chemistry / Ag and NaOCl - or what happened to my silver spoons?

« on: 11/12/2007 18:29:00 »

The most likely answer is that you've oxidized Ag --> Ag+, and reduced the ClO- in the bleach into Cl- (chloride), resulting in the formation of insoluble AgCl on the silver surface.  There are several ways to dissolve AgCl:
 
1) use ~6+ M HCl solution - pool (muriatic) acid should be concentrated enough
2) use 2+ M ammonia solution - household ammonia should be concentrated enough
3) use sodium thiosulfate solution - often used in photographic developing solutions

None of these should harm the underlying silver.

Dick

20

Chemistry / Ionic Compounds In Water

« on: 16/11/2007 16:44:06 »

Regarding suspensions, you're correct.  A suspension is when solid particles are held within a fluid and don't settle out.  The solid particles have to be very small to do this, but not as small as isolated ions.

The bit about hydrogen bonding has some problems with it, however.  It's a common misconception that hydrogen bonding is stronger than other forms of intermolecular forces.  Each type (hydrogen bonding, dipole-dipole, London, etc.) has its own continuum.  Sometimes, the hydrogen bonding forces are stronger, sometimes the London forces are stronger.  Two examples:
  water
     - very strong hydrogen bonding
     - very strong dipole-dipole attractions
     - very weak London forces
  olive oil
     - extremely weak (essentially nonexistent) hydrogen bonding
     - very weak dipole-dipole attractions
     - very strong London forces

Boiling point is mostly dependent on the intermolecular forces present in the molecule.  Which has a higher boiling point?  It's olive oil (~300 °C).  In this case, the London forces present in olive oil are much stronger than all of the combined forces in water.

One last example:
  sucrose (table sugar)
     - very strong hydrogen bonding
     - strong dipole-dipole attractions
     - very strong London forces

net result = very strong intermolecular forces, which helps make sucrose a solid at room temperature

Dick