Question

Calculate the molarity of 90.0 mL of a solution that is 0.92 % by mass NaCl. Assume the density of the solution is the same as pure water.

Answer 1

To calculate the molarity of a 0.92% NaCl solution with a volume of 90.0 mL, convert the mass percentage to grams, turn grams to moles using the molar mass of NaCl, and divide by the volume in liters to find the molarity, which is 0.158 M.

Step-by-step explanation:

The question asks to calculate the molarity of a 0.92% by mass NaCl solution with a volume of 90.0 mL and assuming the density is that of pure water. To solve this, we perform the following steps:

1. Calculate the mass of NaCl in 90.0 mL of the solution using the percentage by mass. Since the density of water is approximately 1 g/mL, 90.0 mL of the solution also has a mass of 90.0 g. Therefore, the mass of NaCl in the solution would be 0.92% of 90.0 g, which equals 0.828 g.
2. Convert the mass of NaCl to moles using NaCl's molar mass. The formula mass of NaCl is 58.44 g/mol. Thus, the number of moles of NaCl is 0.828 g / 58.44 g/mol = 0.0142 moles.
3. Convert the volume of the solution to liters, as molarity is defined as moles per liter. Here, 90.0 mL = 0.090 L.
4. Finally, calculate the molarity by dividing the moles of NaCl by the volume of the solution in liters. Molarity = 0.0142 moles / 0.090 L = 0.158 M (molar).

Answer 2

Answer is: molarity is 0,155 M.
V(solution) = 90,0 mL = 0,09 L.
ω(NaCl) = 0,92% ÷ 100% = 0,0092.
d(solution) = 1 g/mL.
m(solution) = V(solution) · d(solution).
m(solution) = 90 mL · 1 g/mL = 90 g.
m(NaCl) = 90 g · 0,0092 = 0,828 g.
n(NaCl) = 0,828 g ÷ 58,4 g/mol.
n(NaCl) = 0,014 mol.
c(solution) = 0,014 mol ÷ 0,09 L.
c(solution) = 0,155 mol/L.