Quel volume d'ammoniac NH3( g), mesuré à 0^∘ C et sous 1 bar, faut-il dissoudre dans 100 litres

step 1 How many grams of magnesium nitrate must be used to precipitate as magnesium hydroxide, all of t

Quel volume d'ammoniac NH3( g), mesuré à 0^∘ C et sous 1...

Quel volume d'ammoniac $\mathrm{NH}_3(\mathrm{~g})$, mesuré à $0^{\circ} \mathrm{C}$ et sous 1 bar, faut-il dissoudre dans 100 litres d'une solution $1,5.10^{-2} \mathrm{M}$ de nitrate de magnésium $\mathrm{Mg}\left(\mathrm{NO}_3\right)_2$ pour précipiter $99 \%$ de magnésium sous forme d'hydroxyde $\mathrm{Mg}(\mathrm{OH})_2$ ?

Key Concepts

Ideal Gas Law and Standard Molar Volume

The ideal gas law relates the pressure, volume, temperature, and number of moles of a gas. Under standard conditions, such as 0°C and 1 bar, gases have a known molar volume which facilitates the conversion between the measured volume of gas and the amount (in moles) present. Understanding this concept is essential when calculating how much gas is needed to supply the required number of moles of reagent in a chemical reaction.

Reaction Stoichiometry

Reaction stoichiometry is the quantitative relationship between reactants and products in a chemical reaction. In problems involving precipitation, stoichiometry allows one to determine the number of moles of reagents—both in solution and gaseous form—needed to drive a reaction to completion or to a given extent (e.g., 99% precipitation). It provides the framework for linking the amounts of dissolved ions to the required amounts of precipitating agents.

Solubility Product (Ksp) and Precipitation Equilibria

This concept involves understanding the maximum product of the concentrations of the ions of a sparingly soluble salt that can exist in solution without causing precipitation. For salts like magnesium hydroxide, the Ksp determines when the ion product exceeds this threshold, leading to the formation of a precipitate. Mastery of this concept is essential for calculating the conditions under which precipitation occurs and how much of a precipitating agent is needed to achieve a specified percentage of precipitation.

Acid?Base Equilibria of Ammonia in Water

Ammonia, when dissolved in water, undergoes a partial reaction producing ammonium and hydroxide ions according to an equilibrium. Understanding this equilibrium and the basicity of ammonia is crucial because the generated hydroxide ions are responsible for combining with metal cations, such as magnesium, to form insoluble hydroxides. This concept helps in predicting the change in pH and how the equilibrium shifts in response to added ammonia.

Transcript

Please give Ace some feedback