The environmental police of a Brazilian state received a report of contamination of a river by inorganic arsenic, due to the excessive use of pesticides on a plantation on the riverbanks. Arsenic (As) is extremely toxic in its many forms and oxidation states. In nature, especially in groundwater, it is found in the form of arsenate (AsO ₄ ³ ⁻ ), which can be electrochemically reduced to As ⁰   and collected at the cathode of a coulometric cell. In this case, Potentiostatic Coulometry (at 25°C) was performed in an alkaline medium (pH = 7.5 throughout the analysis) to quantify the species. What potential (E) should have been selected/applied to perform the analysis, considering that this is an exhaustive electrolysis technique (until 99.99% of all  AsO ₄ ³ ⁻  has been reduced to  As ⁰  at the electrode, or n( final) = 0.01% n( initial )) and that the concentration of  AsO ₄ ³ ⁻  found in the initial sample was 0.15 mmol/L ?  Data: AsO ₄ 3 ⁻ (aq) + 2 H ₂ O ( l ) + 2 e ⁻ → A s O ₂ ⁻ ( a…

-- 14:17 15. Water-soluble proteins are denatured when there is a change in the pH of the environment in which they are found. This occurs due to the protonation and deprotonation of functional groups present in their structure. Choose the option that indicates the chemical bonds modified by pH in the protein represented in the following figure. E CH2 C-OH CH2 H₂C H₁C CH CH3 CH3 CH CH₂-S-S-CH₂- 910 H B -CH2-CH2-CH2-CH₂-NH3* −0—C—CH₂- ○ A) A, C e D. • В) Вес ○ C) DeE ○ D) B, De E ○ E) A, B e C 68

Suppose sodium sulfate has been gradually added to 100 mL of a solution containing calcium ions and strontium ions, both at 0.15 mol/L. Indicate the alternative that presents the percentage of strontium ions that will have precipitated when the calcium sulfate begins to precipitate. Data: Kps of calcium sulfate: 2.4x10 ⁻ ⁵; Kps of strontium sulfate: 3.2x10 ⁻ ⁷ A) 20,2 % B) 36,6 % C) 62,9 % D) 87,5 % E) 98.7%

14:43 A Candidate Identification docs.google.com 14. The following diagrams represent hypothetical membrane structures with their components numbered from 1 to 6. Based on the figures and your knowledge of biological membranes, select the correct alternative. | 3 5 || 人 2 500000 6 A) Structures 1, 3, 5, 2 and 4 are present in a constantly fluid arrangement that allows the selectivity of the movement ○ of molecules. Structure 4, present integrally or peripherally, is responsible for this selection, while the quantity of 6 regulates the fluidity. B) The membranes isolate the cell from the environment, but allow the passage of water-soluble molecules thanks to the presence of 2 and 3. The membrane in scheme is more fluid than that in 55

12. Mark the correct statement about reactions a and b : a. Br + -OH Br b. + Br H₂O + Br -OH + H₂O A) The reactions are elimination reactions, with reaction "a" being of type E2 and reaction "b" being of type E1. B) Reaction "a" is an E2 type elimination occurring in one step and reaction "b" is an SN1 type substitution. C) Both reactions can result in the formation of carbocation, but in reaction "b" the most stable carbocation will be formed. D) Both reactions occur at the same rate ○ and have the same number of reaction steps. E) Reaction "b" is an E2 type elimination occurring in two steps and reaction "a" is an SN2 type substitution.

Chloroform, long used as an anesthetic and now considered carcinogenic, has a heat of vaporization of 31.4 kJ/mol. During vaporization, its entropy increases by 94.2 J/mol.K. Therefore, select the alternative that indicates the temperature, in degrees Celsius, at which chloroform begins to boil under a pressure of 1 atm. A) 28 B) 40 C) 52 D) 60 E) 72

If we assume a system with an anodic overpotential, the variation of n as a function of current density: 1. at low fields is linear 2. at higher fields, it follows Tafel's law Obtain the range of current densities for which the overpotential has the same value when calculated for 1 and 2 cases (maximum relative difference of 5% compared to the behavior for higher fields). To which overpotential range does this correspond? Data: i = 1.5 mA cm², T = 300°C, B = 0.64, R = 8.314 J K1 mol-1 and F = 96485 C mol-1.

Answer by equation please

Some of the theories used to describe interface structure can be distinguished by:1. the measured potential difference.2. the distribution of ions in solution.3. the calculation of charge density.4. the external Helmoltz plane.