Salad dressing separates into layers after standing is that a chemical change?

No, the separation of salad dressing into layers after standing is not a chemical change; it is a physical change. This separation occurs because the oil and vinegar (or other components) do not mix uniformly, leading to the formation of distinct layers. When stirred or shaken, the dressing can be re-emulsified, indicating that the individual components maintain their original properties.