To find the mass of sodium hydroxide in a solution, multiply the volume of the solution by its concentration to get the number of moles, and then multiply by the molar mass of NaOH. The mass of NaOH in a 30.0 cm³ solution with a concentration of 0.105 mol/dm³ is 0.126 grams.
The mass of sodium hydroxide (NaOH) in 30.0 cm³ of a 0.105 mol/dm³ solution can be calculated using the formula: mass = number of moles × molar mass. To find the number of moles of NaOH, we use the volume of the solution and its concentration. Since the volume needs to be in dm³, we convert 30.0 cm³ to 0.030 dm³ by dividing by 1000 (because 1 dm³ = 1000 cm³). Then we use the concentration of the solution (0.105 mol/dm³) to find the moles of NaOH.
Number of moles = volume × concentration = 0.030 dm³ × 0.105 mol/dm³ = 0.00315 mol of NaOH
Next, we calculate the molar mass of NaOH using the atomic masses of its constituent elements. According to the periodic table:
- Na = 22.990 g/mol
- O = 15.999 g/mol
- H = 1.008 g/mol
Molar mass of NaOH = 22.990 g/mol Na + 15.999 g/mol O + 1.008 g/mol H = 39.997 g/mol
Finally, we find the mass using the molar mass:
Mass of NaOH = number of moles × molar mass = 0.00315 mol × 39.997 g/mol = 0.126 g
30.0 cm³ of a 0.105 mol/dm³ sodium hydroxide solution contains 0.126 grams of NaOH.