In a volumetric analysis experiment, a solution of sodium oxalate (Na₂C₂O₄) in acidic solution in titrated with a solution of potassium permanganate (KMnO₄) according to the following balanced chemical equation

It required 40.0 mL of 0.0335 M KMnO₄ to reach the endpoint. What mass of Na₂C₂O₄ was present initially?
A. 0.179 g
B. 1.79 g
C. 0.0718 g
D. 11.2 g
E. 0.448 g

0.448 g

Explanation:

The first step is to obtain the number of moles of KMnO4 reacted from the data given at end point. We now apply this result together with data from the balanced reaction equation in a simple proportion to obtain the amount of sodium oxalate that reacted. We then calculate the molar mass of the sodium oxalate and multiply this molar mass by number of moles of oxalate reacted in order to obtain the mass of oxalate reacted. See image attached for details.

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.