(a) Calculate the molarity of a solution made by dissolving 12.5 grams of \(\mathrm{Na}_{2} \mathrm{CrO}_{4}\) in enough water to form exactly 750 \(\mathrm{mL}\) of solution. (b) How many moles of KBr are present in 150 \(\mathrm{mL}\) of a 0.112\(M\) solution? (c) How many milliliters of 6.1\(M \mathrm{HCl}\) solution are needed to obtain 0.150 \(\mathrm{mol}\) of \(\mathrm{HCl}\) ?

1. Calculate the molar mass of Na₂CrO₄. To calculate the molarity of the Na₂CrO₄ solution, we first need to determine the molar mass of Na₂CrO₄ using its atomic weights: Na = 22.990 g/mol, Cr = 51.996 g/mol, and O = 15.999 g/mol. Molar mass of Na₂CrO₄ = (2 × 22.990) + 51.996 + (4 × 15.999) = 45.98 + 51.996 + 63.996 = 161.972 g/mol 2. Calculate the moles of Na₂CrO₄. Now we can determine the moles of Na₂CrO₄ by dividing the mass of the solute (12.5 g) by its molar mass (161.972 g/mol). Moles of Na₂CrO₄ = 12.5 g / 161.972 g/mol = 0.07721 mol 3. Calculate the molarity of the Na₂CrO₄ solution. Molarity is defined as the moles of solute per liter of solution. The volume of the solution is given in mL, so first, we need to convert it to liters: 750 mL = 750 / 1000 = 0.750 L Now, we can calculate the molarity of the Na₂CrO₄ solution by dividing the moles of solute (0.07721 mol) by the volume of the solution (0.750 L). Molarity of Na₂CrO₄ solution = 0.07721 mol / 0.750 L = 0.103 M

1. Convert the volume of the solution to liters. The volume of the KBr solution is initially given in mL. To find the moles of KBr present in the solution, we first need to convert the volume from mL to L: 150 mL = 150 / 1000 = 0.150 L 2. Calculate the moles of KBr. Now that we have the volume in liters, we can use the molarity of the KBr solution (0.112 M) to find the number of moles of KBr present in the solution: Moles of KBr = Molarity × Volume = 0.112 M × 0.150 L = 0.0168 mol

1. Calculate the volume of the 6.1 M HCl solution needed. To find the volume of the 6.1 M HCl solution needed to obtain 0.150 mol of HCl, we can use the formula: Volume = Moles of solute / Molarity Using the given molarity (6.1 M) and the moles of solute (0.150 mol), we can find the volume of the solution: Volume = 0.150 mol / 6.1 M = 0.02459 L 2. Convert the volume from liters to milliliters. Since the final answer is requested in milliliters, we can convert the volume from liters to milliliters: 0.02459 L × 1000 = 24.59 mL Approximately 24.59 mL of the 6.1 M HCl solution is needed to obtain 0.150 mol of HCl.