Final answer:
To find the mass of NaCl in a 40 mL solution of 1.8 M NaCl, we multiply the molarity by volume to get the moles, and then multiply the moles by the molar mass of NaCl to get the mass, resulting in approximately 4.2 g of NaCl.
Step-by-step explanation:
To calculate the mass of NaCl in a 40 mL sample of a 1.8 M NaCl solution, we first need to determine the number of moles of NaCl present in the solution using the formula:
Number of moles = Molarity × Volume (in liters)
1.8 M × 0.040 L = 0.072 mol NaCl
Next, we convert the moles of NaCl to grams using the molar mass of NaCl.
Molar mass of NaCl = 58.44 g/mol
Mass of NaCl = Number of moles × Molar mass
0.072 mol × 58.44 g/mol = 4.21 g
Thus, the mass of NaCl in the sample is approximately 4.2 g, rounded to two significant figures as requested.