Question

how to calculate the number of millimoles of S2O32– of each mixture, if we know the volume and concentration of the sodium thiosulfate (Na2S2O3) solution that was pipetted into each reaction mixture.

Answer 1

To calculate the number of millimoles of S2O32− in a reaction mixture, multiply the volume of Na2S2O3 solution (in liters) used by its molarity and then multiply the result by 1,000 to convert moles to millimoles.

Step-by-step explanation:

To calculate the number of millimoles of S2O32− in each reaction mixture, we first need to know the volume (in liters) and molarity (M) of the sodium thiosulfate (Na2S2O3) solution used. Remember, molarity is defined as moles of solute per liter of solution. Once we have these two values, we use the equation:

Moles = Molarity × Volume

To find the moles of Na2S2O3 mixed, we multiply the volume of the solution pipetted into the reaction mixture by its molarity. Since millimoles are a thousandth of a mole, we multiply the resulting moles by 1,000 to obtain millimoles. Here's a step-by-step example applying this process:

• Assuming we pipetted 0.025 L (or 25 mL) of 0.2 M Na2S2O3 solution:
• Moles of Na2S2O3 = 0.2 M × 0.025 L = 0.005 moles
• Millimoles of Na2S2O3 = 0.005 moles × 1,000 mmol/mole = 5 mmol

Note that in analytical chemistry, it's necessary to take into account the stoichiometry of the reaction for complete calculations, especially when reacting with analytes like NaOCl. This approach provides the basic calculation for millimoles based on molarity and volume alone.