Heating up water with salt in a sealed container in a microwave can be dangerous and should be avoided. When water is heated in a sealed container, it can rapidly reach the boiling point without releasing steam. This can lead to a phenomenon called superheating, where the water becomes significantly hotter than its boiling point.
Adding salt to the water can exacerbate this effect. Salt can act as a nucleation site, providing a surface for steam bubbles to form. When the superheated water is disturbed or when an object, such as a spoon or the container itself, is introduced, it can trigger a sudden and violent release of steam. This rapid release of steam can cause the hot water to forcefully erupt from the container, potentially causing burns or other injuries.
To heat water with salt safely, it's important to use an open container that allows steam to escape and prevents pressure from building up. Additionally, it's advisable to add salt to the water after heating or to stir the water well after adding salt to facilitate the dissolving process.
Always follow the manufacturer's instructions and exercise caution when using a microwave to heat substances, especially when dealing with sealed containers or adding substances like salt to water.