The Cultural Influence of Chemistry: Chemistry Definitions
1. Classify the following as either a chemical or physical change.
Burning wood – Chemical since once wood is burned, becomes a new substance. It is transformed from wood to carbon dioxide and water (what about ash? I tried to look up the chemical composition of ash online but didn’t find it easily. One thing I read that I’ve never thought about is that different types of wood are different compounds. Makes sense, but I had never thought about it before)
Crushing a rock – Physical change because the substance of the rock is not changed, it’s just in a different physical state.
Dissolving sugar in water – physical change. A new substance is not made because if the water evaporates, sugar remains.
The rusting of iron – chemical, because a new substance is created as the iron rusts.
2. Classify the following as to whether or not they are pure substances or mixtures.
Milk – is a mixture with ~87% water and the rest emulsions, colloids, molecular and ionic solutions. Depending on the type of milk, it will have varying physical and chemical properties based on where it is found, what the animal drank/ate, hormones it was given, etc. and can have a number of other chemical element or compound present.
Table salt – is a mixture as it may be iodized and have agents that prevent caking. Depending on the type of table salt, it could have different physical and chemical properties based on where it was found (i.e. fleur de sel from one ocean vs. another)
Sugar –The website says that sugar is generally a pure substance. But won’t the sugar have different physical / chemical properties in some situations: Different physical properties: Rock sugar, raw sugar, brown sugar, finely granulized sugar. And won’t sugar have different chemical properties based on how it is processed, such as refined/unrefined?
Steel – mixed. It is made up of a mixture of iron and carbon.
3. A cup of black coffee is considered to be non-homogeneous and a/an impure substance because it combines water and coffee. Also, there is a lot of physical and chemical variability in coffee.
4. The boiling of water is considered to be a physical change and the temperature at which water boils is considered to be a physical property. It is a physical change because the water is changing from one state to another and the temperature at which water boils is a physical property.