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Concentration of Solutions - Introduction

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oncentration of Solutions - Introduction Some measure of the amount of solute dissolved in a solvent is needed when dealing with solutions (particularly aqueous solutions). e.fg. mass per unit volume : g cm-3, kg m-3 or g dm-3 amount per unit volume : mol m-3 or mol dm-3 N.B.: 1 dm3 = 1000 cm3 The amount concentration equation given above can be manipulated to give another useful equation : This equation must be used when dealing with volumes and solutions and must not be confused with another equation giving the amount of substance : back to top Concentration of Solutions - Calculations (1) Question : Sulphuric acid of concentration 0.1 mol dm-3 reacts exactly with 10 cm3 of 0.2 mol dm-3 sodium carbonate(aq). What volume of sulphuric acid is needed? ...read more.


Therefore, the amount of A used = Va � Ca Therefore, the amount of B used = Vb � Cb Since na mol of A reacts with nb mol of B these two equations may be combined to give, nb � Va � Ca = na � Vb � Cb In an examination question you will be given five out of the six pieces of information above and by rearrangement of the mathematical expression the sixth value can be worked out. e.g. in the above worked example between sulphuric acid and sodium carbonate, na = 1 nb = 1 Va = unknown Vb = 10 cm3 Ca = 0.1 mol dm-3 Cb = 0.2 mol dm-3 => Va = 20 cm3 or 0.02 dm3 back to top Titration N.B. ...read more.


The acid can now be added quickly until 1 or 2 cm3 under the volume needed the first time. After that the acid should be added one drop at a time until the just the addition of one drop causes the indicator to change colour. That will be the precise end-point of the reaction. Results sample of results table : titration number final burette reading, cm3 initial burette reading, cm3 volume used, cm3 1 ( rough ) 11.10 0.00 11.10 2 11.10 0.00 11.10 3 10.30 0.00 10.30 4 10.10 0.00 10.10 5 10.05 0.00 10.05 back to top Standard Solution A standard solution is a solution of precisely known concentration. It is generally prepared by dissolving an accurately known mass of solute in an accurately known volume of water. A volumetric flask is used to measure the exact volume of water. A volumetric flask : back to top ...read more.

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