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Monday, June 29, 2009

Chemistry: How were atomic masses measured before mass spectrometry?

How were atomic masses measured before mass spectrometry?

Before the mass spectrometer was invented, how did the earlier scientists determine the mass of an atom (what kind of experiment was performed) ? I realize they were able to find relative mass but I was hoping you would know how they determined actual mass.

Here's a dollar bill. Tell me how thick it is, and you can keep it.
It's too thin to measure with these crummy rulers you've given us, but it's about 0.1 mm.

Close, but not quite. Yes?
It's about 0.045 mm thick.

How did you come up with that?
I rolled it up as tight as I could, counting the number of turns, and then measured the diameter of the roll. I divided that by the number of bill-thicknesses in the roll.

That works. Now here's a five dollar bill. Tell me how to find the mass of a copper atom and you can keep it.
Weigh an atom with a very good scale.

We don't have a scale that good. Our scales won't read masses that are much less than a milligram.
Count out a million copper atoms, weigh them, and divide the weight by a million.

OK. But that would be like like measuring the thickness of a dollar bill with a crummy ruler, because a million atoms is still too light to register on an analytical balance.
All right, a million million.

How are you going to count them out? Are you sure that's going to be enough to give you more than, say, a milligram of material?
Avogadro's number of atoms, then.

How do you put Avogadro's number of atoms on a balance pan?
Put a mole of copper on the pan.

How do you do that?
A mole of copper weighs 63.54 g.

An atom of copper weighs 63.54 g divided by Avogadro's number. 63.54 divided by 6.02×1023 is 1.06×10-22 g per copper atom.

But suppose you didn't know the atomic weight, or Avogadro's number-
Now you're asking two related but different questions: How to find an atomic weight, and how to find Avogadro's number. Those will cost you extra. Pay up for the copper atom first.

You've learned well, grasshopper.


Sunday, June 21, 2009

To All Fathers

HAPPY FATHER'S DAY !!!!!!!!!!!!!!!!!!!!!!!!!!!!

Tuesday, June 16, 2009

Chemistry: Interesting educational videos

Here I found a useful website for students who learn chemistry:

This site introduces viewers to all(or many?) elements in the periodic table with tons of videos, each video for each element. It's a good way to get familiar to your periodic table, now you can watch instead of read to learn them.

The Periodic Table of Videos

In extra, the site below is another creation from University of Nottingham: Sixty Symbols--introducing the symbols used in physics, with videos, too. It's quite interesting and watching it is definitely worth the time.

Sixty Symbols

P/S: All these above are Youtube videos.

Monday, June 15, 2009

STPM Maths Paper 1 Past Year Question

IF u all want to have a look or more understands on past year question of Maths T, below are the link to download STPM maths paper 1 past year question.

*If there is any problems, just visit the website below to download the file*

@#$%-- Maths is FuN --@#$% . . .

Maths T syllabus

For all our information, lower six students will have 16 topics to learn.

STPM Mathematics T (also known as Pure Mathematics) Syllabus
  1. Numbers and Sets
    Real numbers
    Exponents and logarithms
    Complex numbers

  2. Polynomials
    Equations and inequalities
    Partial fractions

  3. Sequences and Series
    Binomial expansions

  4. Matrices
    Inverse matrices
    System of linear equations

  5. Coordinate Geometry
    Cartesian coordinates in a plane
    Straight lines

  6. Functions
    Functions and graphs
    Composite functions
    Inverse functions
    Limit and continuity of a function

  7. Differentiation
    Derivative of a function
    Rules for differentiation
    Derivative of a function defined implicitly or parametrically
    Applications of differentiation

  8. Integration
    Integral of a function
    Integration techniques
    Definite integrals
    Applications of integration

  9. Differential Equations
    Differential equations
    First order differential equations with separable variables
    First order homogeneous differential equations

  10. Trigonometry
    Solution of a triangle
    Trigonometric formulae
    Trigonometric equations and inequalities

  11. Deductive Geometry

  12. Vectors
    Applications of vectors

  13. Data Description
    Representation of data
    Measures of location
    Measures of dispersion

  14. Probability
    Techniques of counting
    Events and probabilities
    Mutually exclusive events
    Independent and conditional events

  15. Discrete Probability Distributions
    Discrete random variables
    Mathematical expectation
    The binomial distribution
    The Poisson distribution

  16. Continuous Probability Distributions
    Continuous random variable
    Probability density function
    Mathematical expectation
    The normal distribution

Saturday, June 6, 2009

Empty Class

haiz...tooo boring ady..duno wanna do wat..
so i'll juz post sum class pics ba... ^^

this is how our class looks like when its skul hoilday...hahaha


Friday, June 5, 2009

1st Post by ME~~~

finally can post on class blog...WAKAKAKA!!!!
anyway, HAPPY HOLIDAYS YA!!!!!!!!