Welcome to DU!
The truly grassroots left-of-center political community where regular people, not algorithms, drive the discussions and set the standards.
Join the community:
Create a free account
Support DU (and get rid of ads!):
Become a Star Member
Latest Breaking News
General Discussion
The DU Lounge
All Forums
Issue Forums
Culture Forums
Alliance Forums
Region Forums
Support Forums
Help & Search
Science
Related: About this forumMore precise estimate of Avogadro's number to help redefine kilogram
From phys.org:
An ongoing international effort to redefine the kilogram by 2018 has been helped by recent efforts from a team researchers from Italy, Japan and Germany to correlate two of the most precise measurements of Avogadro's number and obtain one averaged value that can be used for future calculations. Their results are published this week in the Journal of Physical and Chemical Reference Data.
Avogadro's number is approximately 6.022x10^23an almost unfathomably large quantity, greater than the number of grains of sand on earth or even the number of stars in the universe. But the number, which represents the number of discrete particles like atoms or molecules in a "mole" of a substance, is a useful way to wrangle these tiny particles into more meaningful quantities. A mole of water molecules, for instance, is only a few teaspoons of liquid. Because Avogadro's number is linked to a number of other physical constants, its value can be used to express other units, such as the kilogram.
The team has calculated Avogadro's number several times in the past. Each time, they obtained a value for Avogadro's number by counting the number of atoms in a one kilogram sphere of highly pure Si-28. When silicon crystalizes, it forms cubic cells of eight atoms each. Thus, it is possible to calculate the number of atoms in such a sphere by examining the ratio between the total crystal volume and the volume occupied by each silicon atom, which can in turn be calculated by measuring the cubic cell.
Earlier this year, the group obtained a new value for Avogadro's number with an uncertainty of less than 20 atoms per billiondown from a 30-atom uncertainty in their 2011 value. But because both numbers have some degree of uncertainty, albeit a tiny one, it is more accurate to correlate them and then average them into one more neutral value: 6.02214082(11)x10^23. The number in parentheses represents the uncertainty of the last digit in the result.
more ...
Avogadro's number is approximately 6.022x10^23an almost unfathomably large quantity, greater than the number of grains of sand on earth or even the number of stars in the universe. But the number, which represents the number of discrete particles like atoms or molecules in a "mole" of a substance, is a useful way to wrangle these tiny particles into more meaningful quantities. A mole of water molecules, for instance, is only a few teaspoons of liquid. Because Avogadro's number is linked to a number of other physical constants, its value can be used to express other units, such as the kilogram.
The team has calculated Avogadro's number several times in the past. Each time, they obtained a value for Avogadro's number by counting the number of atoms in a one kilogram sphere of highly pure Si-28. When silicon crystalizes, it forms cubic cells of eight atoms each. Thus, it is possible to calculate the number of atoms in such a sphere by examining the ratio between the total crystal volume and the volume occupied by each silicon atom, which can in turn be calculated by measuring the cubic cell.
Earlier this year, the group obtained a new value for Avogadro's number with an uncertainty of less than 20 atoms per billiondown from a 30-atom uncertainty in their 2011 value. But because both numbers have some degree of uncertainty, albeit a tiny one, it is more accurate to correlate them and then average them into one more neutral value: 6.02214082(11)x10^23. The number in parentheses represents the uncertainty of the last digit in the result.
more ...
InfoView thread info, including edit history
TrashPut this thread in your Trash Can (My DU » Trash Can)
BookmarkAdd this thread to your Bookmarks (My DU » Bookmarks)
2 replies, 584 views
ShareGet links to this post and/or share on social media
AlertAlert this post for a rule violation
PowersThere are no powers you can use on this post
EditCannot edit other people's posts
ReplyReply to this post
EditCannot edit other people's posts
Rec (3)
ReplyReply to this post
2 replies
= new reply since forum marked as read
Highlight:
NoneDon't highlight anything
5 newestHighlight 5 most recent replies
More precise estimate of Avogadro's number to help redefine kilogram (Original Post)
Jim__
Jul 2015
OP
DetlefK
(16,423 posts)1. Avogadro's number is the ratio between the weight of a C12-atom and 12 gram.
We need it to calculate how much of a given substance is in a given weight.
Ghost Dog
(16,881 posts)2. Succinctly and appositely expressed, thanks. n/t