Question

extension questions

1. it is often useful to separate matter. physical methods of separation (filtering, distillation) do not require a chemical change. in other words, no chemical bonds are broken or formed during the separation. chemical methods of separation (decomposition, electrolysis) require a chemical change. in other words, chemical bonds are broken and/or formed during the separation.

a. is straining cooked pasta from water a physical or chemical separation?
b. is using a fuel cell to separate water into hydrogen and oxygen a physical or chemical separation?
c. which type(s) of matter (mixtures/compounds/elements) could be separated by physical methods?
d. which type(s) of matter (mixtures/compounds/elements) would need to be separated by chemical methods?

1. students in a chemistry course were asked the following question on a unit exam: \draw a diagram representing an element using circles as atoms.\

a. the following diagrams represent two typical answers given by students. which drawing is the best representation of an element? explain.
b. imagine that the atom in drawing b had been removed by physical separation from one of the substances in model 1. what substances could have been the source of the atom in drawing b?

Explanation:

Step1: Analyze straining pasta from water

Straining cooked pasta from water is like filtering. No new substances are formed, and no chemical - bonds are broken or formed. So it is a physical separation.

Step2: Analyze fuel - cell separation of water

Using a fuel cell to separate water into hydrogen and oxygen involves a chemical reaction where water molecules are broken down into hydrogen and oxygen molecules. Chemical bonds in water are broken, so it is a chemical separation.

Step3: Determine matter separable by physical methods

Mixtures are made up of different substances that are not chemically combined. Physical methods can be used to separate the components of a mixture based on differences in physical properties like size, solubility, boiling point etc. Compounds and elements, on the other hand, require chemical changes to be separated into their constituent parts. So mixtures can be separated by physical methods.

Step4: Determine matter separable by chemical methods

Compounds are substances made up of two or more elements chemically combined. To separate the elements in a compound, chemical bonds must be broken, which requires a chemical change. Elements are the simplest form of matter and cannot be separated into simpler substances by chemical or physical means. So compounds need to be separated by chemical methods.

Step5: Analyze element representation

An element is a pure substance made up of only one type of atom. Drawing A shows multiple atoms of the same type, which is a better representation of an element since elements are composed of many identical atoms in nature. Drawing B shows only one atom, which is not a typical representation of how elements exist in bulk.

Step6: Analyze source of atom in Drawing B

If the atom in Drawing B was removed by physical separation, the source could be a mixture containing that single - type of atom. For example, a mixture of noble - gas atoms (like a sample of argon gas) where the atoms are not chemically bonded to other atoms and can be separated by physical means such as condensation or diffusion.

Answer:

a. Physical separation
b. Chemical separation
c. Mixtures
d. Compounds
16a. Drawing A is the best representation of an element because elements are composed of many identical atoms in nature, and Drawing A shows multiple atoms of the same type.
16b. A mixture containing single - type atoms (such as a noble - gas mixture) could be the source.