Energy changes
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How would I plan to measure the concentration of sodium hydroxide if I didn't know it using calorimetry (thermochemistry)? Even if I did the experiment and found the enthalpy change of neutralisation when 2 mol dm-3 NaOH is mixed against HCl, how can I calculate and prove the concentration of NaOH? What are the calculations and equations I need to to this?
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Corrie writes ...
You will find in books that the enthalpy (heat) change for the neutrailisation of a strong acid, like HCl, with a strong alkali, like NaOH, is more or less constant at -57 kJ per mole of water formed, i.e. neutralising 1 mole of NaOH produces 57 kJ of heat energy.
So, if you neutralise a known volume of your NaOH solution, say 50 cm3, with a slight excess of HCl (you'll need to do some preliminary experiments to find out how much HCl is needed) in an insulated cup experiment, and measure the temperature change, you can work out the amount of energy released by the neutralisation, using the familiar q = m x C x temp. change formula. Let's say it works out to be Z kJ.
Since neutralising 1 mole of NaOH will release 57 kJ of energy, the amount ot NaOH in your cup must have been Z/57 moles of NaOH. As you know the volume of NaOH you used, you can now work out the concentration.
Risk assessment
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updated: 14 April 2008
