If the mass of both the reactants is 10kg then the mass of the products also equals 10kg.
It is due to the law of conservation of mass.
Mass can neither be created nor be destroyed.
Answer:
1. pH = 1.23.
2. 
Explanation:
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1. In this case, for the ionization of H2C2O4, we can write:

It means, that if it is forming a buffer solution with its conjugate base in the form of KHC2O4, we can compute the pH based on the Henderson-Hasselbach equation:
![pH=pKa+log(\frac{[base]}{[acid]} )](https://tex.z-dn.net/?f=pH%3DpKa%2Blog%28%5Cfrac%7B%5Bbase%5D%7D%7B%5Bacid%5D%7D%20%29)
Whereas the pKa is:

The concentration of the base is 0.347 M and the concentration of the acid is 0.347 M as well, as seen on the statement; thus, the pH is:

2. Now, since the addition of KOH directly consumes 0.070 moles of acid, we can compute the remaining moles as follows:

It means that the acid remains in excess yet more base is yielded due to the effect of the OH ions provided by the KOH; therefore, the undergone chemical reaction is:

Which is also shown in net ionic notation.
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Limestone and marble are the two rocks that are easily weathered by carbonic acid. Two kinds of weathering mostly affect the rocks. and they are physical weathering and chemical weathering. The above mentioned two rocks are highly affected by carbonic acid. The appeareance of these kind of rocks change their structure due to erosion very regularly. Caronation is the type of chemical weathering that affects the rocks limestone and marble. The carbonic acide is formed by the reaction of carbon dioxide in the air and water in the rivers. This carbonic acid results in weathering.
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