- The best method to determine the melting point is by using a machine that is called “DSC” that stands for “Differential Scanning Calorimetry”. - DSC machine is a simple furnace, this furnace it heats up what is inside from a low temperature (e.g. 50) to a high temperature like 300. This machine can be programmed to heat from one heat to other that you can determine. Inside this furnace we have 2 chambers; one we call it the reference & the other we call it the sample. Reference chamber is left empty (only air). Sample chamber is where we place the solid material to be analyzed ( we can use here small quantities like 5-10 mgs). 2 | P a g e
Techno1 Dr.Ahmed Bani Jaber Sheet#4 Done by: Noor Aswad - The two chambers are connected by sensors that have a software of a PC to analyze the data & this software makes a plot between ▲ T (difference in temp. between the sample & the reference chambers) versus T of reference. - When no endothermic (spend energy) (e.g. melting) or exothermic (expel energy) (e.g. degradation) processes take place then the temperature of both the reference & the sample chambers they will increase in parallel in a way ▲ T = zero & the machine will give a plot like the following thermogram : - Reference will not be affected because already it has air (no melting or rxn), but the one who determines the difference is the sample, so if the sample doesn’t undergo any rxn then it will increase in the same manner of the reference & the machine will plot on zero. - If an endothermic process takes place then the temperature of the sample chamber will be held constant during this process and until the process is completed. 3 | P a g e
Techno1 Dr.Ahmed Bani Jaber Sheet#4 Done by: Noor Aswad - Till the end of the melting, the temperature of the sample chamber id held constant, the reason is that when melting happens then the heat input from the furnace into the sample chamber will be consumed as “ latent heat of fusion ” → the heat absorbed by 1 mole of the substance in order to be converted from the solid state to the liquid state. - Example on this, when you bring ice from freezer & put the ice outside →it’s temperature will remain zero until all the ice disappears (melting ends) then the temperature of water will start to rise above zero.
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- Spring '18
- Glass, Noor Aswad, Bani Jaber