1) Answer is: c. 9.
Balanced chemical reaction: C₅H₈ + 9O₂ → 8H₂O + 5CO₂.
Accordin to law of conservation of mass, there are eighteen oxygen atoms on both side of balanced chemical reaction.
This is example of combustion.
Combustion is reaction with oxygen.
Organic compound reacts with oxygen and produce carbon dioxide and water.
2) Answer is: c. Only the oxygen needs to be balanced. There are equal numbers of hydrogen and carbon.
According to principle of mass conservation, number of atoms must be equal on both side of chemical reaction.
There are two oxygen atoms on the left and six oxygen atoms on the right side of chemical reaction so chemical reaction is not balanced.
Balanced reaction of ethane combustion: C₂H₄ + 3O₂ → 2H₂O + 2CO₂.
3) Answer is: Hydrogen and chlorine need to be balanced. There is an equal amount of magnesium on each side.
According to principle of mass conservation, number of atoms must be equal on both side of chemical reaction.
There is one hydrogen atom on the left and two hydrogen atoms on the right side of chemical reaction so chemical reaction is not balanced.
There is one chlorine atom on the left and two chlorine atoms on the right side of chemical reaction so chemical reaction is not balanced.
Balanced reaction of ethane combustion: Mg + 2HCl → H₂ + MgCl₂.
4) Answer is: c. sugar stirred in tea.
Solution is homogeneous mixture has the same proporties of its components throughout any given sample, composed of two or more substances.
Solution has a uniform composition and is able to be separated by physical means.
In aqueous solution, solvent is water and solute (in this example sugar) is a substance dissolved in water.
Other examples are heterogeneous mixture.
Heterogeneous mixture is not uniform in composition.
