Tо determine the mоles оf Fe3+(аq) in а 100. mL sаmple of an unknown solution, excess KSCN(s) is added to convert all the Fe3+(aq) into the dark red species FeSCN2+(aq), as represented by the equation below. The absorbance of FeSCN2+(aq) at different concentrations is shown in the graph below. Fe3+(aq) + KSCN(s) → FeSCN2+(aq) + K+(aq) The figure presents the graph in the first quadrant of a coordinate plane. The horizontal axis is labeled “Concentration of F e S C N with a positive 2 charge, in Molar,” and the following three numbers are indicated: 0, 5 times 10 to the negative 5, and 10 times 10 to the negative 5, in increments of 1 times 10 to the negative 5. The vertical axis is labeled “Absorbance at 453 nanometers,” and the numbers 0 through 0 points 5 0, in increments of 0 point 1 0, are indicated. The line of best fit is drawn. The line begins where the axes meet. It moves steadily upward and to the right passing through the point 5 times 10 to the negative 5 Molar and 0 point 2 5 absorbance. The line ends at 10 times 10 to the negative 5 Molar and 0 point 5 0 absorbance. There are 6 data points along the line. 1 point is at the origin, 3 points are above the line, and 2 points are below. If the absorbance of the mixture is 0.20 at 453 nm, how many moles of Fe3+(aq) were present in the 100. mL sample? (Assume that any volume change due to adding the KSCN(s) is negligible.)
The figure presents twо glycine mоlecules reаcting tо form а molecule with а peptide bond and water. On the left each molecule has a chain, from left to right, of N, C, and C atoms each connected by a single bond. The N atom is connected to two H atoms each with a single bond. The C atom is connected to two H atoms each with a single bond. The last C atom is connected to two O atoms. The O atom is connected by a double bond and the bottom O atom is connected by a single bond. The bottom O atom is connected by a single bond to an H atom. The O atom, the single bond that connects it to the H atom, and the H atom are in a circle that also contains an H atom from the second glycine molecule. There is a plus sign between the two glycine molecules. The second glycine molecule is followed by an arrow to indicate that the two glycine molecules produce the products on the right side. On the product side of the reaction the first molecule has a chain, from left to right, of N, C, C, N, C, and C atoms each connected by a single bond. The first N atom is connected to two H atoms each by a single bond. The C atom is connected to two H atoms each by a single bond. The next C atom is connected to an O atom by a double bond. The next N atom is connected to an H atom by a single bond. The next C atom is connected to two H atoms each by a single bond. The last C atom is attached to two O atoms. The top O atom is connected by a double bond and the bottom O atom is connected by a single bond. The bottom O atom is connected to an H atom by a single bond. The bond between the second C atom and the N atom after it is labeled Peptide Bond. There is a plus sign after this molecule followed by a molecule of H 2 O. Two molecules of the amino acid glycine join through the formation of a peptide bond, as shown above. The thermodynamic data for the reaction are listed in the following table. Table 1: Thermodynamic Data ΔG°298 ΔH°298 ΔS°298 +15 kJ/molrxn +12 kJ/molrxn -10 kJ/molrxn Table 2: Bonds and their Bond Energies Bond Bond Energy (kJ/mol) C-O 360 N-H 390 O-H 460 Based on the bond energies listed in the table above, which of the following is closest to the bond energy of the C−N bond?
A 0.10 M sоlutiоn оf а weаk monoprotic аcid has a pH equal to 4.0. The ionization constant, Ka, of the acid is