Ions in Solutions (5A) - Chem & Physics

1. Which ions are spectator ions when $\text{AgNO}_3(aq)$ reacts with $\text{NaCl}(aq)$?

   $\text{Na}^+$ and $\text{NO}_3^-$. Spectator ions do not participate in the reaction, remaining unchanged in solution.

2. Identify the correct expression for ion concentration: $0.15\,\text{M }\text{AlCl}_3$ gives what $[\text{Al}^{3+}]$?

   $[\text{Al}^{3+}]=0.15\,\text{M}$. AlCl$_3$ provides one Al$^{3+}$ ion per molecule, matching the salt's molar concentration.

3. What is the key distinction between strong and weak electrolytes?

   Strong: ~complete dissociation; weak: partial dissociation. Strong electrolytes fully ionize into ions, while weak ones establish an equilibrium with partial ionization.

4. State the boiling point elevation formula for an electrolyte solution.

   $\Delta T_b=iK_b m$. Boiling point elevation uses the van 't Hoff factor for the effective particle concentration from dissociation.

5. What is the van 't Hoff factor $i$ for $\text{NaCl}$ assuming complete dissociation?

   $i=2$. NaCl dissociates into two ions, Na$^+$ and Cl$^-$, affecting colligative properties accordingly.

6. Which way do water molecules orient around a cation in solution?

   Oxygen ends point toward the cation. Water's dipole orients with the negative oxygen toward positive cations for electrostatic stabilization.

7. What is the van 't Hoff factor $i$ for $\text{Al}_2(\text{SO}_4)_3$ assuming complete dissociation?

   $i=5$. Al$_2$(SO$_4$)$_3$ produces five ions: two Al$^{3+}$ and three SO$_4^{2-}$, in complete dissociation.

8. What is the definition of molality $m$?

   Moles solute per kilogram of solvent. Molality expresses concentration independent of temperature, focusing on solvent mass for colligative properties.

9. What is the van 't Hoff factor $i$ for an ideal nonelectrolyte?

   $i=1$. Nonelectrolytes do not dissociate, contributing only one particle per molecule in colligative properties.

10. Identify whether $\text{BaSO}_4$ is expected to be soluble or insoluble in water by common solubility rules.

    Insoluble. BaSO$_4$ has low solubility due to strong lattice energy exceeding hydration energy.

11. What is the solubility rule for Group $1$ metal salts (e.g., $$$\text{Na}^+$$, $$\text{K}^+$$)?

    All Group $1$ salts are soluble in water. Group 1 cations form highly soluble salts due to their low charge density and high hydration.

12. What is the definition of an electrolyte in aqueous solution?

    A solute that produces ions in water and conducts electricity. Electrolytes ionize in water, enabling the flow of electric current through the movement of charged particles.

13. What is the solubility rule for all nitrate salts, $$$\text{NO}_3^-$$, in water?

    All nitrates are soluble in water. Nitrate ions form soluble compounds with most cations due to their high hydration energy.

14. What is the definition of a hydrated ion in water?

    An ion surrounded by oriented water molecules (hydration shell). Ions in water attract polar water molecules, forming a structured layer due to electrostatic interactions.

15. What is the van 't Hoff factor $i$ for $\text{CaCl}_2$ assuming complete dissociation?

    $i=3$. CaCl$_2$ dissociates into three ions: one Ca$^{2+}$ and two Cl$^-$, for colligative calculations.

16. What is the relationship between ionic charge density and hydration strength?

    Higher charge density implies stronger hydration. Ions with higher charge per volume attract water more strongly, enhancing solvation energy.

17. What is the net ionic equation for precipitation when $\text{AgNO}_3(aq)$ is mixed with $\text{NaCl}(aq)$?

    $\text{Ag}^+(aq)+\text{Cl}^-(aq)\rightarrow\text{AgCl}(s)$. The net ionic equation shows only the species that form the precipitate, excluding spectators.

18. What is the definition of molarity $M$?

    Moles solute per liter of solution. Molarity measures solute concentration per volume of solution, useful for stoichiometric calculations.

19. State the freezing point depression formula for an electrolyte solution.

    $\Delta T_f=iK_f m$. Freezing point depression incorporates the van 't Hoff factor to reflect the number of particles from electrolytes.

20. Identify the correct expression for ion concentration: $0.15\,\text{M }\text{AlCl}_3$ gives what $[\text{Cl}^-]$?

    $[\text{Cl}^-]=0.45\,\text{M}$. AlCl$_3$ dissociates into three Cl$^-$ ions per unit, tripling the chloride concentration.

21. Which way do water molecules orient around an anion in solution?

    Hydrogen ends point toward the anion. Water dipoles align with positive hydrogens facing negative anions to minimize energy in the hydration shell.

22. State the formula for ionic strength $I$ of a solution in terms of ion concentrations and charges.

    $I=\frac{1}{2}\sum c_i z_i^2$. Ionic strength quantifies the total concentration of ions, weighted by the square of their charges.

23. What is the definition of a nonelectrolyte in aqueous solution?

    A solute that does not produce ions in water; no conductivity. Nonelectrolytes remain molecular in solution, preventing ion formation and thus electrical conduction.

24. State the formula for osmotic pressure $$$\pi$$ of a dilute solution.

    $\pi=iMRT$. Osmotic pressure accounts for the van 't Hoff factor to include effects of ionic dissociation in dilute solutions.

25. Identify the correct expression for ion concentration from a salt: $0.20\,\text{M }\text{CaCl}_2$ gives what $[\text{Cl}^-]$?

    $[\text{Cl}^-]=0.40\,\text{M}$. CaCl$_2$ dissociates to release two Cl$^-$ ions per formula unit, doubling the chloride concentration.

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