Chapter 9: Solutions and Mixtures and Concentrations and Solubility and Dilutions Study Notes; short notes

Ismail Serageldin, former Vice President of the World Bank, famously noted that future wars would be fought over water due to scarcity and population growth.
Earth is more than two-thirds water, but only 3% is freshwater. Less than one-third of that (approximately 1% of total planet water) is available to humans; the remainder is in glaciers and ice caps.
Freshwater quality is threatened by pollutants like toxic chemicals, antibiotics, steroids, minerals, and ionic compounds.

A mixture contains two or more different substances, unlike pure elements or compounds.
Heterogeneous mixtures (e.g., chocolate chip cookie dough, granite) have unevenly distributed components and visible separate phases. They are typically opaque or cloudy.
Homogeneous mixtures (e.g., tea, salt water) appear as a single substance or phase and are usually translucent. These are formally called solutions.
Phases: Chemists identify separate liquid phases based on polarity (e.g., a mixture of oil and water contains two distinct liquid phases).

Solutions consist of two parts:
- Solvent: The major component doing the dissolving.
- Solute: The minor component being dissolved.
Solutions can exist in all physical states:
- Solid: Steel (Iron solvent; Carbon, nickel, copper, zinc, or chromium solutes).
- Liquid: Seawater (Filtered water solvent; Salts and organic matter solutes).
- Gaseous: Air (Nitrogen solvent; Oxygen, argon, neon, methane, helium, $CO_2$ , and $NO_2$ solutes).

Suspension: A mixture where solid particles are suspended in a liquid and eventually settle over time (e.g., chocolate milk, liquid antibiotics).
Colloidal Suspension: A mixture with particles so small they stay suspended indefinitely (e.g., milk, oobleck). These possess both liquid and solid properties.

Solubility is the extent a solute dissolves in a solvent under specific conditions.
Rule of Thumb: "Like dissolves like." Polar substances (e.g., sugar, salt) dissolve in polar solvents (e.g., water), while nonpolar substances (e.g., butter, octane, benzene) dissolve in nonpolar solvents (e.g., vegetable oil, kerosene).
Hydration: The process where water molecules surround dissociating ions. This involve energy changes:
- Endothermic: Absorbs energy, used in cold packs (e.g., ammonium nitrate crystals in water).
- Exothermic: Releases energy, used in heat packs (e.g., calcium chloride or sodium acetate in water).
Insoluble Compounds: Some ionic solids, like Barium sulfate ( $BaSO_4$ ), are insoluble despite being ionic because water cannot overcome the strong internal bonds.

Group $1A$ cations and Ammonium ( $NH_4^+$ ) are soluble.
Nitrates ( $NO_3^-$ ) are soluble.
Halides ( $F^-$ , $Cl^-$ , $Br^-$ , $I^-$ ) are soluble except with $Hg_2^{2+}$ , $Pb^{2+}$ , and $Ag^+$ .
Sulfates are soluble except with $Ba^{2+}$ , $Ag^+$ , $Sr^{2+}$ , and $Pb^{2+}$ .
Compounds not containing these ions are generally insoluble.

Temperature (Solids/Liquids): Typically increases as temperature increases due to higher kinetic motion and more frequent collisions.
Pressure (Gases): Solubility increases as pressure above the solution increases.
Temperature (Gases): Solubility decreases as temperature increases; higher kinetic energy allows gas molecules to break intermolecular bonds and escape.
Scuba Safety: Pressure underwater increases by $1\,atm$ every $33\,feet$ . High pressure increases dissolved nitrogen levels, leading to nitrogen narcosis or decompression sickness ("the bends"). Treatment involves the hyperbaric chamber ( $7\,atm$ or more).

Unsaturated: More solute can be added.
Saturated: No more solute will dissolve at a given temperature/pressure.
Supersaturated: Contains more solute than should be possible; unstable and prone to crystallization (e.g., maple syrup, rock candy).
Concentration Formulas:
- $\text{Percent by mass} = \frac{\text{mass of solute (g)}}{\text{mass of solution (g)}} \times 100$
- $\text{Percent by mass-volume} = \frac{\text{mass of solute (g)}}{\text{volume of solution (mL)}} \times 100$
- $\text{Parts per million (ppm)} = \frac{\text{mass of solute (g)}}{\text{volume of solution (mL)}} \times 10^6$
- $\text{Parts per billion (ppb)} = \frac{\text{mass of solute (g)}}{\text{volume of solution (mL)}} \times 10^9$

Molarity (M): $\frac{\text{moles of solute}}{\text{liters of solution}}$ . Essential for chemical laboratory precision.
Molality (m): $\frac{\text{moles of solute}}{\text{kg solvent}}$ . Used when particles per kilogram are critical (e.g., boiling point elevation).
Dilution Formula: $M_{\text{concentrated}} \times V_{\text{concentrated}} = M_{\text{dilute}} \times V_{\text{dilute}}$ .

Q: Classify hot chocolate, white wine, apple juice, and vinegar/oil dressing.
A: Hot chocolate and vinegar/oil are heterogeneous; white wine and apple juice are liquid solutions.
Q: Identify solvent/solute in tap water and sports drinks.
A: Tap water: water (solvent), calcium/magnesium/fluoride ions (solutes). Sports drink: water (solvent), sugar/potassium/sodium ions (solutes).
Q: Predict solubility of octane, benzene, isopropanol, and potassium chloride in water vs kerosene.
A: Octane ( $C_8H_{18}$ ) and Benzene ( $C_6H_6$ ) are nonpolar/soluble in kerosene. Isopropanol ( $CH_3CHOHCH_3$ ) is polar/soluble in water. $KCl$ is ionic/soluble in water.
Q: Calculate mass of sodium hypochlorite in a $125\,g$ sample of $5.0\%$ bleach.
A: $125\,g \times \frac{5.0\,g}{100\,g} = 6.3\,g\,NaOCl$ .
Q: Determine perchlorate mass in $100\,L$ of water at $4\,ppb$ .
A: $100\,L \times \frac{4\,\mu g}{1\,L} = 400\,\mu g$ , which is $4 \times 10^{-4}\,g$ .
Q: Calculate the molarity of $45.0\,g\,HCl$ in a $750\,mL$ solution.
A: $45.0\,g \div 36.46\,g/mol = 1.23\,mol$ . $1.23\,mol \div 0.750\,L = 1.64\,M$ .