(Originais Teachy 2023) - Question Easy of Chemistry

Among the amphoteric oxides, what is the oxidation number of chromium, respectively, in these compounds?

The search for alternative and more sustainable energy sources has led to the development of fuels composed of mixtures with ideal combustion characteristics. One of the challenges in this process is the improvement of the energy efficiency of internal combustion engines, which depends, in part, on the uniformity of the fuel mixture. Considering an internal combustion engine, where the efficiency of the fuel burning process is directly related to the homogeneity of the air-fuel mixture, a chemical engineer decides to investigate the behavior of different mixtures under pressure and temperature conditions similar to those found in the combustion chamber. For his analysis, he selects two mixtures: the first one is atmospheric air, mainly composed of nitrogen (78%), oxygen (21%), and other gases in lower concentrations, known to be a homogeneous mixture; the second one is a mixture of ethanol and water, in which ethanol and water form two distinct phases due to their differences in polarity and intermolecular interactions, considered a heterogeneous mixture. Based on the concepts of homogeneous and heterogeneous mixtures, which of the two mixtures investigated is more suitable to be used as fuel in an internal combustion engine, considering the goal of maximizing the energy efficiency of the burning process?

Organic salts are compounds derived from the reaction of an inorganic base with a carboxylic acid. These compounds have distinct characteristics from inorganic salts, such as solubility in organic solvents and soap and detergent properties. A classic example of an organic salt is sodium acetate, which can be obtained by the reaction of acetic acid with sodium hydroxide. Given the formula of acetic acid (CH3COOH), identify the inorganic base that, when reacting with acetic acid, forms sodium acetate. This reaction is an example of:

A chemical reaction A + 2B -> C + D occurs in a system where the initial concentrations of A and B are, respectively, 0.1 mol/L and 0.2 mol/L. After a period of time, the concentration of A decreased to 0.05 mol/L. Considering that the reaction is first order with respect to A and second order with respect to B, determine the overall order of the reaction and explain how you reached this conclusion.