Let's start with question 2, since you asked about that first. An element is the simplest form of matter and can't be broken down chemically into other substances. A compound is a pure substance made of two or more elements combined in a fixed ratio. A mixture is not a pure substance. It can be homogeneous, which means it's evenly distributed, but its composition can vary.
Now we'll use the information given to decide how each substance fits these definitions:
A: This is a compound because upon heating it produced two other substances.
B: This is a compound because it can be formed by the chemical reaction of two other substances.
C: This is most likely an element. It's used, along with D, to form a new chemical compound. However it could also be a compound because compounds can be reactants in chemical reactions.
D. This is most likely an element, but could be a compound, as it forms a new compound when reacted with C.
E. This is a compound. It's broken down into its elements by electrolysis.
G: This is an element as we're told that it can't be further decomposed.
Based on the type of initial reaction (thermal decomposition) and the mass and mole ratios of substances involved, the initial compound could be calcium carbonate:
`CaCO_3 -> CaO + CO_2`
`C + O_2 -> CO_2`
`CaO -> 2 Ca + O_2`
`CaO + H_2O -> Ca(OH)_2`
The amounts given work becasue:
10 g CaCO3 = 0.1 mol
5.6 g CaO = 0.1 mol
4.4 g CO2 = 0.1 mol
1.6 g O2 = 0.05 mol
1.3g/.0.3 g is the mass ratio of CaO to Ca(OH)2
So if A is calcium carbonate (a compound), then the other substances are:
B: carbon dioxide, CO2, compound
C: carbon, element
D. oxygen, element
E. calcium oxide, CaO, compound
G: oxygen gas, O2, compound
L. Calcium hydroxide, Ca(OH)2, compound
Some physical properties that might be used to distinguish between substances are:
- state - solid, liquid or gas
- solubility in water
- magnetic properties
Here are some examples for each pair of substances given:
Steel and aluminum: Steel is more dense than aluminum and steel is attracted to a magnet while aluminum is not.
Water and sodium chloride solution: Water is less dense than NaCl solution, NaCl solution conducts electricity and water does not, and evaporation of NaCl solution will leave a residue of solid NaCl.
Water and motor oil: motor oil is less dense than water and will float on top of it when the two are combined. Motor oil is more viscous (thicker) than water.
FeS and a mixture of FeS: FeS is a compound and will be uniform in appearance and all one color. A mixture of Fe and S will have both black and yellow particles. These particles can be separated with a magnet while FeS can't be separated by physical means.