In scientific terms, Italian salad dressing would best be described as a mixture. To understand why, we'd need to first understand the difference between elements, compounds, and mixtures.
What is an element?
- The main criteria in determining an element is that it consists of only one kind of atom, for example Carbon.
- An element is identified by the number of protons in its nucleus.
- An element cannot be broken down, but can exist as either a single atom (for example Helium) or as a molecule (two or more atoms held together by covalent bonds (i.e. Nitrogen).
What is a compound?
- A compound consists of two or more DIFFERENT types of elements bound together.
- This bond can be broken by chemical means, but not physical means.
- The properties of a compound are different from the properties of the individual elements that make it up.
What is a mixture?
- Is made up of two or more elements or compounds that are physically joined.
- The various components of a mixture can be separated by physical methods.
- A mixture often shares or retains the properties of its individual components.
Based on the rules determined above, Italian salad dressing would be considered a mixture because it is a combination of various components including vinegar, vegetable oil, bell peppers, sugar syrup and various herbs and spices that have been joined by physical means, and which can also be separated by physical means.
Not so Italian salad dressing
Interestingly, the idea of a pre-mixed vinaigrette based salad dressing would be decidedly foreign to most Italians, who usually dress their salads with olive oil, salt, vinegar and occasionally black pepper.
The type of 'Italian salad dressing' referred to in the question is actually more often used in North America, but is probably labelled 'Italian' due to its use of Mediterranean herbs including oregano, fennel, and dill.