Cut the carrots into quarters and remove the tough inner core. Cut the slices into 2” pieces.
Press the saute mode of your Instant Pot and melt the 1/2 cup of butter. Add the carrots and stir to coat with butter. Sprinkle over the salt and baking soda. Pour in the water. Stir.
Secure the lid and set the vent to sealing. Pressure cook on high for 20 minutes. Do a quick release of the pressure.
Add the chicken stock and puree the soup in the pot with an immersion blender (or in a blender or food processor) until smooth. Heat on saute mode, no longer than 3 minutes. Turn off saute mode.
Add the final 2 tbsp of butter and again puree with the immersion blender until the butter has melted and blended in.