Question

Based on the information given, classify each of the pure substances as elements or compounds, or indicate that no such classification is possible because of insufficient information. Analysis with an elaborate instrument indicates that substance A contains two elements. substance B and substance C react to give a new substance D. substance E decomposes upon heating to give substance F and substance G. heating substance H to 1000 ∘C causes no change. substance I cannot be broken down into simpler substances by chemical means. substance J cannot be broken down into simpler substances by physical means. heating substance K to 500 ∘C causes it to change from a solid to a liquid.

Answer 1

Answer:

Analysis with an elaborate instrument indicates that:

• Substance A contains two elements.

   

               Compound

• Substance B and substance C react to give a new substance D.

              Insufficient information

• Substance E decomposes upon heating to give substance F and substance G.

            Compound

• Heating substance H to 1000 °C causes no change.

          Insufficient information

• Substance I cannot be broken down into simpler substances by chemical means.

               Element

• Substance J cannot be broken down into simpler substances by physical means

              Insufficient information

Explanation:

Important background:

• Pure substances are elements or compounds.

• Elements are formed by only one kind of atoms. They cannot be broken down into another substance by chemical or physical means. There are only 118 known elements; they are all listed in the periodic table.

• Compounds have fixed chemical composition and are formed by two or more kind of atoms, chemically bonded. They can be broken down into different pure substances, either elements or other substances, only by chemical changes.

With tha information let's see every statement about the pure substances that should be classified as elements or compounds.

• Substance A contains two elements: compound

   

               Since, the pure substance contains two elements, it is not just and element by a compound. This is because a compound is a pure substance composed of two or more elements.

• Substance B and substance C react to give a new substance D.: Insufficient information

        Either two elements, one element and one compound, or two compounds may react to give a new substance, so you cannot assure what kind of pure substance B and C are.

For instance:

    - two elements like hydrogen and oxygen reacto to give water (a compound)

  - a compound like CH₂=CH₂ react with an element like Cl₂ to give CH₂Cl-CH₂Cl

• Substance E decomposes upon heating to give substance F and substance G. : Compound

An element cannot be decomposed into two different substances, since the elements are composed by just one kind of atoms.

So, if the substance E decomposes into two different substances, F and G, E necessarily has to be a compound.

• Heating substance H to 1000 ∘C causes no change. Insufficient information

The mere fact that a substance has not changed by heating at such extreme temperature cannot assure whether the substance is a compound or an element.

Some compounds are stable at very high temperatures. For instace, magnesium oxide, MgO, has a melting point of 2852°C, meaning that it will remain a a solid substance way beyond 1,000°C

• Substance I cannot be broken down into simpler substances by chemical means. Element

Since an element is formed by one single kind of atoms, it cannot be broken down into simpler substances by chemical means; but a compose does, because it is formed by two or more different elements chemically bonded.

• Substance J cannot be broken down into simpler substances by physical means: Insufficient information

The distintion between compounds and elements is based on chemical changes; the fact that physical changes do not change the substance does not tell anything about the fact that the substance is composed by one kind of elements or several elements chemical boonded.

Hence, physical means do not provide sufficient information to conclude about whether a substance is an element or a compound.