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Standard Solutions

Standard Solutions. Definition Choosing a Standard Solution Making the Solution. Standard Solutions. A standard solution one that we know the exact concentration of

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Standard Solutions

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  1. Standard Solutions Definition Choosing a Standard Solution Making the Solution

  2. Standard Solutions • A standard solution one that we know the exact concentration of • They are used in a volumetric analysis to help us calculate the concentration of another solution. Therefore we must be certain of the concentration of our standard • Only certain chemicals can be used in the production of a standard solution…

  3. Choosing a Standard • Before we make up a standard solution we must make sure of a few things first: • The standard must be chemically stable during storage (i.e. it can’t react with air or water or itself…) • It must have a known formula (i.e. CuSO4.5H2O) • It isn’t allowed to absorb water from the air (it can’t be hygroscopic) • We must be certain of the fast, complete, balanced reaction with the chemical of unknown concentration • It must be pure (analytical quality)

  4. Making Up The Solution - Calculations • First use c = n/v to calculate the amount and volume required to make your standard solution. • Then turn the amount into mass using m = Mrn Example: We want 250ml of 0.100molL-1 Na2CO3 • c = 0.100molL-1, v = 0.250L, n = ? • n = cv = 0.100 x 0.250 = 0.0250mol • n = 0.0250mol, Mr = (2x23 + 12 + 3x16) = 106gmol-1, m = ? • m = Mrn = 106 x 0.0250 = 2.65g • In other words we need to add 2.65g of the Na2CO3 to 250ml of water to make a 0.100molL-1 solution

  5. Making the Standard Solution – The Process • Each step of the process is design to ensure the right mass of the standard gets into the right volume of water • Accurately weigh the mass out with a balance onto a piece of filter paper. Write down the exact mass you used. • Use a funnel to transfer the mass to a clean, correct sized volumetric flask i.e. 250ml. Ensure that you do not drop anything. • Wash off the paper and funnel with distilled water from the wash bottle. All of the mass must end up in the flask. • Fill the flask ¾ full of water. Stopper and invert to mix until dissolved. • When dissolved, carefully fill up to the mark with distilled water. Invert to mix. • Calculate the concentration (based on the mass and volume you used) and write it onto the flask.

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