hermanntrude

From what I remember from physics lessons at school if you look carefully at steam issuing from a boiling kettle the steam will seem to appear to form a little distance away from the spout. Therefore it cannot be seen until it starts to condense. That was in the days when kettles were boiled on a gas ring and could be kept boiling for the observation. These days with electric kettles which automatically shut off it's not so easy! (Not to mention 'elf an safety)

however, steam has a different refractive index to air so it'd be visible by the way objects behind it would appear distorted. transparent, yes, invisible, i'd say not.

you might be able to make a polyatomic ion out of xenon atoms minus a few electrons, or even maybe just one. I think [Ne2]+ is predicted to be stable

maybe the hydrogen is getting diluted by air thats in the headspace of the first conical flask. if you reduce the headspace(prefferably eliminate it entirely) then it could work.

this is one of the things i tried. it failed horribly. i think the headspace is necessary to allow cooling of the water vapor. i did notice that with a smallish headspace was best, and gave heavy bubbles which after a few minutes became lighter.

i'm going to buy a cylinder and be done with it, but i've also decided to get rid of the horribly rusty chlorine cylinder first

I tried all the above suggestions and also a few more.

I managed to get floating bubbles by using zinc and fairly concentrated H2SO4 (created by putting zinc in water and adding swigs of conc acid as needed), but it wasn't reproducible... the bubbles floated sometimes and sometimes not. And i could never get the bubbles to break off of the larger mass, they just made snakes which stood up

your bubbles are too much water, not enough hydrogen.

 

probably due to small bubbles.

 

a quick fix for this(if it is indeed to cause) would be to put a small cap over the metal shavings to catch the bubbles and allow them to form larger bubbles before getting to the surface. although i'm not sure how that will be affected by the soap, they might not join as easily.

the bubbles are already doing that. I have a side-arm conical flask which has the acid and metal in, with a stopper in it, a tube running from th side arm to another conical which has an inlet tub below the surface of some soapy water and an outlet leading to a small glass funnel. the bubbles are probably a centimeter or so in diameter on average

What about the size of your bubbles? If your bubbles are too small, the weight of the bubble will hold it down. Are you trying to generate the hydrogen in the soap water, or in a separate reaction bubbled into the soap water? In either case, your rate of hydrogen generation can't really compete with a hydrogen cylinder.

The bubbles are smallish but should be big enough. i've tried a number of setups but all involving an acid and a metal (i've settled on 1M HCl and Mg for speed of delivery without getting dangerously hot), and in each case i've run the hydrogen through a separate bubbler. I'm thinking about this a lot and i'm thinking the only thing it can be is water vapor weighing down the bubbles. The bubbles are of comparable size to those in videos ive seen. I found only one video involving floating bubbles which didn't use a cylinder, and that used aluminum, which I will try tomorrow. i'm thinking perhaps aluminum has a lower enthalpy change for the reaction with HCl and so less water gets vaporised. I'll also try running it through a longer tube before bubbling it and if i get desperate i'll try a drying tube

I've been attempting to recreate this experiment (link), but without using a hydrogen cylinder. The only problem is, that no matter which acid or metal i use, no matter how fast i generate the gas, my bubbles don't float. They burst into flame nicely but they don't float. I'm not sure what's causing the bubbles to be so heavy... is it gaseous water?

OK this is a volumetric analysis question, which always goes like this

step 1: calculate number of moles of known substance used

step 2: use stoichiometry to find number of moles of unknown substance used

step 3: use information from step 2 to find whatever it was you were asked for

step 1 is simple. find the number of moles of HCl. This involves the equation c = n/V

step 2 requires you to write a balanced equation for the reaction of [ce]Na2CO3[/ce] with HCl (remember that the waters of crystallization will not be involved in this reaction so you can leave them out).

step 3 involves using the number of moles of [ce]Na2CO3[/ce] from step 2, along with the original mass of the solid with the waters of crystallization to calculate the value of x in [ce]Na2CO3.xH2O[/ce]

most carcinogens work in small quantities over long periods of time. A single dose just once is probably not going to be trouble.

This ended up on the BBC!!!

 

http://news.bbc.co.uk/1/hi/world/africa/10301713.stm

 

Original video at

awesomeness

there's no harm in stating the obvious, as well, in nice clean scientific terms. Physiology is a science too, after all.

technically, a guy making moonshine is several things.

A biochemist, a sythetic chemist, a brewer, a criminal, and in many cases, foolhardy.

A real help in understanding stereochemistry is to use a molecular modelling kit. If you dont have one or can't afford one, many institutions (schools, colleges, universities) will allow you to borrow one for a while. If that isn't true, try using cocktail sticks and pieces of sticky tack. Use coloured markers to distinguish between cocktail sticks

my advice to students who are concerned about organic chemistry is do some review

the basics are vital for understanding organic chemistry. here's a short list of stuff you'll find useful to remember

- skeletal diagrams

- aromatic rings

- isomerism

- formal charges

- electronegativity

- chatelier's principle

remember to ask lots of questions, and be prepared to spend a lot of time working on assignments and review your notes while you study the course (not just before the exam!).

There are some really good chemists here who will be able to help if you're getting stuck, but remember they usually take their time in answering, so study early!

Cu+ has an annoying tendency to oxidize to Cu2+. i don't know if that might be trouble in the suggested reaction...

i'm sorry, i don't know the naming systems well enough to help you. I could guess, but i suspect that it's all about priorities, and as such the hydroxy compounds might be named in a different order to the acetyl compounds. You could try using chemdraw... it can name compounds once you've drawn them

these are nonsensical compounds. You can't have a (C≡C) group 4 times. Carbon only bonds 4 times, and in the compound shown, many of the carbons would have 6 carbons. Perhaps it's supposed to be (-C≡C)4?

Here is a way to compute the number of ways to generate all possible sums of m tosses of a die with n faces. Use the generating function, which for a fair die of n faces is [math]g(z) = z+z^2+\cdots+z^n[/math]. Next compute [math]g(z)^m[/math], where m is the number of tosses. Finally, read off the polynomial coefficients. For example, the number of ways to get a total of three is the coefficient of [math]z^3[/math] in [math]g(z)^m[/math].

 

Here is a perl script that computes and prints this:

#!/usr/bin/perl -w
use strict;
sub mult_poly($$);
my ($tosses,  # Number of tosses of the die
   $faces,   # Number of faces on the die
   $gen,     # Generating polynomial g(z)
   $pow);    # g(z)^m

# Get command line arguments. Usage is <script_name> [#tosses [#faces]]
$tosses = scalar @ARGV ? shift : 2;
$faces  = scalar @ARGV ? shift : 6;

# Construct the generating function, g(z)=z+z^2+...i+z^n, n=#faces.
$gen = [0, (1) x $faces];

# Compute g(z)^m, m=#tosses
$pow = [1];
$pow = mult_poly $pow, $gen foreach (1 .. $tosses);

# Print results.
printf "%3s %9s\n", qw(N Count);
printf +("%3d %9d\n", $_, $pow->[$_]) foreach ($tosses .. $#$pow);

# Sanity check; the printed sum should be n^m.
my $s = 0;
map {$s += $_} @$pow;
printf "Sum %9d\n", $s; 


# Multiply two polynomials.
sub mult_poly ($$) {
  my ($p, $q) = @_; 
  my $prod = [(0) x ($#$p + $#$q + 1)];
  for (my $ip = 0; $ip <= $#$p; $ip++) {
     for (my $iq = 0; $iq <= $#$q; $iq++) {
        $prod->[$ip+$iq] += $p->[$ip] * $q->[$iq];
     }   
  }   
  return $prod;
}

---

Merged post follows:

Consecutive posts merged

The above might overkill if you don't want all possible combos. If all you want the number of ways to achieve a specific sum s given t tosses of a die with f faces,

 

Ooops. What I posted for this individual problem doesn't work. Deleted.

 

For now use the algorithm in the first half of this multi-post.

I'm fairly sure your method will work, but i'm not sure if excel can handle it. Basically I have developed an excel spreadsheet which generates 256 random integers between 1 and 6. It then takes the sum of however many dice you want to throw (user input), and plots the result on a frequency graph. I have written/recorded some macros which allow me to throw the dice multiple times (up to 10,000), although i don't understand visual basic at all. What i want to do is compile a list of possible totals for a specific number of dice (perhaps not as many as 256, but a large amount) and the number of ways of throwing each possible total.

Can it be done in excel?

i'm impressed at how much effort you put into telling me you didn't know.

The function I need is one which calculates the number of permutations which add to "n", using "l" six sided dice.

for example if i was using a single die (l=1), and i wanted to know how many ways there were to get a 4 (n=4), the function would return 1. If i were using 2 dice (l = 2) and i wanted to know how many ways there were to get a 7 (n = 7), the function would return 6 (1,6; 6,1; 5,2; 2,5;4,3; 3,4).

I know it's going to be based on the old nPr function but it's more complex than that i think.

I intend to incorporate it into an excel spreadsheet to demonstrate entropy and numbers of microstates.

2,2-dimethylpropane (aka neopentane, sometimes it's just called dimethylpropane). But if you're naming it systemically, you have to include the 2,2- part so it's unambiguous about exactly where those methyl groups are situated.

actually the 2,2 part isn't necessary because if the methyl groups were on the 1- or the 3- positions, the parent chain would be longer and there'd be an entirely different name.

from wikipedia:

IUPAC nomenclature retains the trivial name neopentane. The systematic name is 2,2-dimethylpropane, but the substituent numbers are unnecessary because it is the only possible "dimethylpropane".

this is a smallish forum, it takes a while to get answers. sometimes u won't get them at all, especially if the question doesn't interest people.

In ammonium, the positive charge is considered to be mostly on the nitrogen (it has what we call a formal charge of +1. Formal charges are best learned by reading. try google). Ammonium is entirely symmetrical and none of the bonds is any different to the others, although one is formed by the donation of the lone pair on ammonia to an empty s-orbital in an H+ ion.

dative bonds form for the same reason any bond forms: because it can. the positive-negative-positive arrangement of nucleus-electrons-nucleus is quite stable.

u can potassium chkoride as oxdiser to make good burn

you mean potassium chlorate

If you don't know the difference between a chlorate and a chloride, please stop giving people chemistry advice before you kill someone.

Ive never used it. I imagine the main danger other than it's corrosiveness would be the possibility of accidentally releasing large amounts of Br2 and other noxious bromine compounds

you are assuming all of the water is gaseous. If it is all gaseous, then yes, you will want 2378.3L to contain that much steam at that temperature and pressure. However, the pressure will change as the water boils. Boiling anything inside a closed container can be extremely dangerous because of the high pressures built up. I hope you know what you're doing.