Uppose you perform a titration of an unknown weak acid solution. You start with 4.00 mL of the weak acid and find that it takes 12.8 mL of 0.0500 M NaOH to reach the equivalence point. What is the concentration of the unknown weak acid solution?

Explanation:

It is known that at the equivalence point,

     Equivalent of acid = equivalent of base ......... (A)

and,     Equivalent =

Therefore, equivalent of acid is calculated as follows.

     Equivalent of acid = .......... (1)

     Equivalent of base = ............ (2)

Hence, using equation (A) we will calculate the concentration as follows.

                       M = 0.16 M

Thus, we can conclude that concentration of the unknown weak acid solution 0.16 M.                    

answer is: c. the experiment shows that the red substance experienced a chemical change.

this is chemical change (chemical reaction), because two new substances are formed (metalig liquid and gas), the atoms are rearranged and the reaction is followed by an energy change.

this is example of chemical decomposition.

chemical decomposition (analysis) is the separation of a single chemical compound into its two or more elemental parts or to simpler compounds.  

chemical decomposition is opposite of chemical synthesis.