What mass of NaOH should be dissolved in sufficient water to get 20 m^3 of an aqueous solution

step 1 So in this question PS is close to 7 .0 and hence contribution of water is considered let water

What mass of NaOH should be dissolved in sufficient water to...

What mass of NaOH should be dissolved in sufficient water to get $20 \mathrm{~m}^{3}$ of an aqueous solution of $\mathrm{pH}, 7.3$, at $25^{\circ} \mathrm{C}$ ?
(a) $0.16 \mathrm{~g}$
(b) $1.6 \times 10^{-4} \mathrm{~g}$
(c) $0.04 \mathrm{~g}$
(d) $0.12 \mathrm{~g}$

Key Concepts

Mass-Mole Conversion using Molar Mass

Once the number of moles of a substance needed to achieve the desired ion concentration is determined, it is converted to mass using the molar mass. This conversion is a fundamental step in quantitative chemical preparation, linking the theoretical calculations to practical measurements.

Molarity and Volume Conversion

Molarity, defined as the number of moles of solute per liter of solution, is a key concept for solution preparation. Additionally, being able to convert between units of volume, such as from cubic meters to liters, is essential for accurately determining the total number of moles required in the overall solution.

Strong Base Dissociation

Strong bases like NaOH dissociate completely in aqueous solution. This means that the concentration of added NaOH directly translates into an equivalent concentration of hydroxide ions. This concept is important when calculating how adding a specific mass of a strong base affects the overall pH of the solution.

Water Ionization and the Ion Product Constant (Kw)

Water undergoes autodissociation to form hydrogen ions and hydroxide ions, and the product of their concentrations is a constant (Kw), which is 10^-14 at 25°C. Understanding this concept is crucial because even pure water has inherent concentrations of H+ and OH-, and this baseline must be considered when adjusting the ion concentrations to achieve a desired pH.

pH and pOH

The concepts of pH and pOH are fundamental in acid-base chemistry. pH is a measure of the hydrogen ion concentration while pOH is a measure of the hydroxide ion concentration. At 25°C, their sum is 14. This relationship allows one to calculate the concentration of one ion from the other, which is essential when preparing solutions with a specific pH.

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