which of the following is a physical change?
Milk becomes sour
An iron nails rusts
All the water in a solution of salt water evaporates leaving a lot of crystals of salt in the bottom of the dish
A wooden log is burned leaving ash in the fireplace
To determine which of the following is a physical change, we need to understand the characteristics of physical change. In a physical change, the chemical composition of the substance remains the same, but there is a change in its physical properties such as shape, size, or state of matter.
Now, let's analyze each option:
1. Milk becomes sour: This is not a physical change as the sourness of milk indicates a chemical change caused by the presence of bacteria. The chemical composition of milk changes, making it an example of a chemical change.
2. An iron nail rusts: Rusting is a chemical reaction that involves the combination of iron, oxygen, and moisture. Therefore, this is not a physical change but a chemical change.
3. All the water in a solution of saltwater evaporates, leaving a lot of crystals of salt in the bottom of the dish: This is a physical change. Evaporation is a process that changes the state of matter from the liquid phase (water) to the gaseous phase (water vapor), leaving behind the dissolved salt as solid crystals. The chemical composition of salt remains the same, only its physical state changes.
4. A wooden log is burned, leaving ash in the fireplace: Burning a wooden log is a chemical change. The combustion of wood involves a chemical reaction that produces heat, light, and various gases, leaving behind solid residue or ash. The chemical composition of the wood is altered during the burning process.
Therefore, the correct answer is: All the water in a solution of saltwater evaporates, leaving a lot of crystals of salt in the bottom of the dish.