 In the first part of Hess's law, we will measure the heat of solution of solid sodium hydroxide. You will mass out approximately one gram of solid sodium hydroxide. Then place 50 milliliters of water into your calorimeter. You will use your temperature probe to measure the initial temperature of the water. When the temperature reading has stabilized, you will then add the sodium hydroxide. You will stir the mixture and record the highest temperature reached. In the second part of our Hess's law lab, we are going to measure the heat of neutralization of an aqueous solution of sodium hydroxide with an aqueous solution of HCl. We place the HCl into the calorimeter. We put our temperature probe into the calorimeter and measure the initial temperature of the solution. We add the sodium hydroxide solution and stir the mixture and record the highest temperature reached.