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Q1: What factors determine how much solute can dissolve in a solvent?
Solubility depends on the physical and chemical properties of both the solute and solvent. The polarity of each substance is critical—polar solvents dissolve polar solutes, while nonpolar solvents dissolve nonpolar solutes, following the principle that like dissolves like. Additionally, pH, temperature, and pressure influence solubility, with temperature typically increasing dissolution rates.
Q2: How does temperature affect the solubility of a compound?
Solubility typically increases with increasing temperature. For example, sugar dissolves more readily in hot coffee than in iced coffee. Sodium carbonate demonstrates this trend, with solubility rising from 7 g per 100 mL at 0°C to 44 g per 100 mL at 100°C, though some compounds show exceptions to this pattern.
Q3: What is a saturated solution and why does additional solute remain undissolved?
A saturated solution contains the maximum amount of solute dissolved in a given solvent volume. At this equilibrium point, dissolved ions balance with solid solute, so any additional solute cannot dissolve and remains as a precipitate. For instance, 36 grams of sodium chloride in 100 mL of water at room temperature creates a saturated solution.
Q4: How do you calculate the equilibrium constant for a dissolution process?
For dissolution equilibria, the equilibrium constant Kc uses concentrations of dissolved products in the numerator and reactants in the denominator, each raised to their stoichiometric coefficient. For ionic salts, the solubility product constant Ksp simplifies this by setting solid concentrations to 1, yielding Ksp = [A]^x[B]^y for compounds AxBy.
Q5: What does a negative ΔG value tell you about a dissolution reaction?
A negative ΔG indicates the reaction is spontaneous, meaning the system has sufficient energy to proceed without external input. Gibbs free energy, calculated from ΔG = ΔH – TΔS, reveals whether a dissolution process releases or requires energy. Negative values show the system naturally favors the dissolved state over the undissolved crystalline form.
Q6: How do enthalpy and entropy influence whether a solute dissolves?
Enthalpy measures heat content change; positive ΔH indicates endothermic dissolution (absorbs heat), while negative ΔH indicates exothermic dissolution (releases heat). Entropy measures disorder; dissolution increases solute disorder but orders solvent molecules around it. Together, these properties determine whether the system prefers the ordered crystalline state or the disordered dissolved state.
Q7: Why does sodium chloride dissolve differently in various solvents?
Solubility varies by solvent because different solvents have different polarities and solvation capabilities. Sodium chloride has a solubility of 36 g per 100 mL in water, but only 1.1 g per 100 mL in methanol and 0.034 g per 100 mL in dimethylformamide. Polar ionic compounds dissolve best in polar solvents that can effectively solvate the dissociated ions.