Sciencemadness Discussion Board

Density

tom haggen - 30-11-2003 at 11:03

is density always measured in the units of grams/cubic centimeters (g/cm3)? because on this website www.roguesci.org/megalomania/synthesis3.html#nitric it doesn't specify the units. also if all i have is a measuring container that measures liquid in milliliters and I need to know how much that is in cubic centimeters could someone remind me of the simple conversion between these 2 units of measurement, sorry about the elementry math questions but better safe than sorry

-tom

Blind Angel - 30-11-2003 at 11:15

1 ml = 1cm<sup>3</sup>

[Edited on 30-11-2003 by Blind Angel]

thx

tom haggen - 30-11-2003 at 12:07

that what my hypothesis was thanks for clearing that up. as for the website I read farther and found water, and saw the density for that was 1 so i know what units hes using now.

P.S. im starting to like the metric system a little more now

-tom

[Edited on 30-11-2003 by tom haggen]

[Edited on 30-11-2003 by tom haggen]

axehandle - 14-2-2004 at 02:57

The metric system is superior in every way.

For example, if I say that my penis is 18cm long, it sounds better than 7 inches.... =)

Edit: I'm drunk now.


[Edited on 2004-2-14 by axehandle]

hodges - 14-2-2004 at 05:17

Isn't density measured relative to water? I don't think the units (metric or other) matter.

thunderfvck - 14-2-2004 at 11:10

Yeah, denstiy is measured relative to water. We say that 1 gram of water is 1 ml. I guess it doesn't matter about the units because the geenral idea is derived with respect to water, but metric is so much easier!

Hermes_Trismegistus - 14-2-2004 at 13:02

Quote:
Originally posted by Blind Angel
1 ml = 1cm<sup>3</sup>

[Edited on 30-11-2003 by Blind Angel]


Yes, But only of pure water at standard temperature and pressure!

and if something has a quoted density of say 1.816 it refers to 1.816 grams per cubic centimeter (at standard temperature and pressure).


(just wanted to make one final clarifying statement.)

vulture - 14-2-2004 at 13:13

For water it's not at the standard temperature; it's the density measured at 4C or 277,15K.

density vs specific gravity

Magpie - 14-2-2004 at 20:48

Density is in absolute units, e.g. g/ml, g/cm3, etc. Density of water at room temperature would be slightly less than 1 g/cm3.

Specific gravity is a number without units that is referenced to some standard material at some standard condition, normally H2O at 1 atm and 4 deg C. Specific gravity of mercury at room temperature would be about 13, IIRC.

Hermes_Trismegistus - 14-2-2004 at 21:28

Quote:
Originally posted by vulture
For water it's not at the standard temperature; it's the density measured at 4C or 277,15K.


Is that because, it is at that temperature that liquid water is at its most dense?

jimwig - 15-2-2004 at 16:35

there is a neat device for measuring the density of solids.

its a container with a spill way on it to catch all the liquid displaced from placing a solid in the liquid.

weigh the solid
weigh the water it displaces

ration equals density ratio

gold = 19 something

t_Pyro - 16-2-2004 at 02:00

Quote:
Originally posted by jimwig
there is a neat device for measuring the density of solids.


It's called a "eureka can", after Archimede's exclamation.

unionised - 22-2-2004 at 07:23

The SI unit of density is the Kg/m^3 Beware of this when looking at data from physics books (They think the density of water is about a thousand).
Strictly the density of water isn't 1 g/ cm^3 but it is 1 g/ ml. The difference is about 27 parts in a million and I don't see that mattering much. (It's because they couldn't make the prototype kilogram agree with the prototype metre to better than that accuracy).

jimwig - 3-3-2004 at 13:31

are not a ml and cc^3 the same amount?

[Edited on 3-3-2004 by jimwig]

t_Pyro - 8-3-2004 at 02:53

There's no such thing as cc^3. If what you mean is 1<b>cm<sup>3</sup></b> or cc (cubic centimetre), the answer is yes.

1m is defined as the path traveled by light in vacuum in 1/299,792,458 of a second.
1Kg is equal to the mass of the international prototype of the kilogram, a certain platinum-iridium cylinder.

For more details, see <a href="http://physics.nist.gov/cuu/Units/current.html">this</a>.

[Edited on 8-3-2004 by t_Pyro]

I am a fish - 8-3-2004 at 03:24

Quote:
Originally posted by t_Pyro
There's no such thing as cc^3.


#include &lt;pedantry.h&gt;

There is in 9-dimensional or higher space.

t_Pyro - 10-3-2004 at 02:12

PEDANTRY

n : a ostentatious and inappropriate display of learning

From dictionary.com.

Forgive me, because I'm still one of the lesser mortals limited to a paltry 3 dimensions. You're absolutely right, though.

tom haggen - 11-3-2004 at 17:34

So if I have some 35% NaOH that weighs somewhere around 1.41g/cm3. does that mean that it is 35% NaOH by weight or does it mean that it is 35% NaOH by volume. I used a density chart to calculate concentration.

t_Pyro - 12-3-2004 at 09:41

35% NaOH could be w/w (weight per weight) , or w/v (weight per volume) .

If it's w/v, that means there is 35 gms of pure NaOH per 100 ml of the solution. That amounts to a molarity of 35/40*10= 8.75 M

If it's w/w, that means that there is 35 gm of pure NaOH per 100 gm of the solution. If the density is 1.41g/cm<sup>3</sup>, that amounts to a molarity of (35/40)/(100/1.41)*1000 = 12.3375 M. Note the difference in the two values.

If the concentration was written on a laboratory reagent bottle, it most probably refers to w/w composition. If that's the case, the relative density will also be printed on the label.

concentration expressed in %

Magpie - 12-3-2004 at 19:16

Tom, I'd say that if you have what is normally a solid dissolved in a liquid then it will be wt%. However, if you have a liquid dissolved in a liquid then it will likely be vol%, like alcohol in water for alcoholic beverages or food flavorings.

Chemists are pretty good about giving you the basis, but consumer products are notoriously poor.

Gas in gas is normally vol%, which is also mole %.

[Edited on 13-3-2004 by Magpie]

tom haggen - 12-3-2004 at 19:53

well i think i'm going with weight because after all I weighed 100ml of this solution and it weighed 141grams. So i determined that it was like 35% sodium hydroxide. Thats were it fell on the density chart if I remember correctly. so if I have 141grams of 35% NaOH than I have 49grams of pure NaOH.

axehandle - 15-3-2004 at 17:01

I'm so very grateful that I've grown up using the SI metric system... :)

amen

Magpie - 15-3-2004 at 19:35

Somewhat off topic, but yes, what a pain it is to have to be able to work between 2 or more systems of units. As a chemical engineering student and as a practicing engineer I have had to be able to convert constantly between metric and English. What a colossal waste of time. The US government periodically issues mandates about going metric but the English system is so entrenched that it is going slowly. I have to keep 2 complete wrench sets to be able to keep stuff repaired around the house, cars, etc.

axehandle - 16-3-2004 at 04:25

Like someone once said: "You approach the metric system inch by inch". :)

12AX7 - 2-4-2005 at 06:57

Quote:
Originally posted by Magpie
I have had to be able to convert constantly between metric and English.


Fuck the French and their system. :D

sparkgap - 2-4-2005 at 07:04

I take it to mean that you are, shall I say, "anti-metric", Tim. Why?

Titan, WTF are you on to????

sparky (^_^)

12AX7 - 2-4-2005 at 19:20

Quote:
Originally posted by sparkgap
I take it to mean that you are, shall I say, "anti-metric", Tim.


I just love making comments that:
1. Offend group "A"
2. Make group "B" laugh at group "A"

:P

Seriously, I don't mind conversion factors...keeps 'ya sharp :D

Tim