Answer: You need to use 5.75 grams of NaCl to make a 2.81 L of a 0.035 M solution.
Explanation: To calculate the mass of NaCl required to make a 2.81 L of a 0.035 M solution, you can use the formula:
mass = moles x molar mass
where moles = volume x molarity.
First, calculate the moles of NaCl required:
moles = volume x molarity
moles = 2.81 L x 0.035 mol/L
moles = 0.09835 mol
Next, calculate the molar mass of NaCl, which is the sum of the atomic masses of sodium and chlorine:
molar mass = 23.0 g/mol + 35.5 g/mol
molar mass = 58.5 g/mol
Finally, use the formula to calculate the mass of NaCl required:
mass = moles x molar mass
mass = 0.09835 mol x 58.5 g/mol
mass = 5.75 g
Therefore, you need to use 5.75 grams of NaCl to make a 2.81 L of a 0.035 M solution.