Answer:
<em />
- <em>19. C₂H₂, HF, and H₂O₂ are molecular compounds</em>
<em />
- <em>20. The formula is CuSO₄. 5H₂O</em>
Explanation:
<u><em>Question 19.</em></u>
The three the chemical formulae in red, C₂H₂, HF, and H₂O₂, represent compounds because a compound is the chemical union of two or more atoms of different kind.
The chemical union is done either by ionic bonds or covalent bonds.
C, H, F, and O are all non-metal elements. Non-metals combine each other through covalent bonds, which is the bond in which electrons are shared to complete the valence shell. Ionic bonds are formed by the electrostatic atraction between ions of different charge and is typical of the bond between a metal and a non-metal.
Thus, all the bonds are covalent and the compounds are molecular compounds.
<em></em>
<u><em>Question 20. </em></u>
<em></em>
You can determine the chemical formula using the molar masses of both Copper(II) sulfate and water.
- Molar mass of copper(II) sulfate: 159.609 g/mol
- Molar mass of water: 18.015 g/mol
Call n the number of water molecules in the molecular formula:
The ratio of water to copper(II) sulfate is:
- n × molar mass of water / molar mass of the compound
- n × 18.015 / (n × 18.015 + 159.609) = 36%
- 18.015n = 0.36(18.015n + 159.609)
- 18.015n = 6.4854n + 57.45924
Therefore, the formula of the hydrate contains 5 molecules of water and it is CuSO₄.5H₂O.
