Wednesday, December 14, 2011

Weight per Volume

Hari ni nak wat entry ilmiah sket. Kenapa?? Sebab tadi nak jumpe Sifu nak tunjuk calculation, tertibe diri menjadi konfius, weight kite measure in gram tapi camane ngan volume? mL ke L? ke kne pkai PPM??. Makanya Encik Google telah menolongku. Dan dengan itu aku rase berminat nak share sket info ni khas untuk chemist yang pelupa cam aku ni. How to calculate percent for weight per volume...

First of all, what is weight per volume itself??
Percent weight per volume is defined as the grams of solute in 100 milliliters of solution. The calculation provides information about the concentration of the solution. A percentage expresses the number of parts of a particular substance per 100 total parts. The solute is a substance present in the solution in an amount less than that of the solvent. This calculation is most useful when the solute is a solid while the overall solution is a liquid.

How to calculate??
  • 1 - Start with the amount of solute you know to be present in the solution, expressed in grams.

  • 2 - Determine the total volume in milliliters of the solution.
  • 3 - Divide the grams of solute by milliliters of solution (result of Step 1 divided by result of Step 2).
  • 4 - Multiply the resulting number (of Step 3) by 100 to get the percent weight per volume.
  • **
    Percent weight per volume should always be calculated using grams for the solute and milliliters for the solution. Be sure to convert to these units if they are not already in use.

    And, how to covert from percent to molarity??

  • 1

    Write down the chemical formula for the compound in your solution. This formula will specify the elements in the compound and how many atoms of each element are in a molecule of that compound. If you had a salt solution, for example, you would write out the chemical formula for sodium chloride; NaCl.

  • 2

    Look up the atomic weight for each element in the chemical formula. You can find these weights on a standard periodic table of the elements. In the case of the example, the atomic weight of sodium (Na) is 22.99 and that of chlorine (Cl) is 35.45.

  • 3

    Multiply each element's atomic weight by the number of atoms of that element per molecule of compound. Add together all the products of those multiplications. The value you obtain will be the gram molecular weight of that chemical, in units of grams per mole. For NaCl, there is only one sodium atom and one chlorine atom per molecule, so you would calculate:

    (1)(22.99) + (1)(35.45) = 58.44 grams per mole.

  • 4

    Multiply the value of percent concentration by 10. Since percent weight per volume is grams chemical per 100 milliliters solution, this calculation gives the grams of chemical in each liter of solution -- because there are 1,000 ml in a liter. If a solution of NaCl is 12 percent, you would multiply that value by 10 to determine there are 120 g of NaCl per liter.

  • 5

    Divide the value of grams you just calculated by the gram molecular weight of the chemical. This calculation provides the number of moles of chemical per liter of solution, which is the definition of molarity; at this point you have converted the original percent concentration into molarity. In the case of the NaCl solution, 120 g divided by 58.44 g per mole gives a molarity of 2.05.

    **Make sure your percent concentration is a percent weight per volume, since there are other types of percent concentrations.

    source: ehow
  • simple rite?? hehehe... enjoy your calculating!

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