medchem prelab week 6

Pre-Lab Q1: Behavior of Ammonia in Aqueous Solutions

• Behavior: Ammonia acts as a weak base by accepting a proton from water.
• Reaction Equation: $NH_3 + H_2O \rightleftharpoons NH_4^+ + OH^-$
• Solution Nature: Alkaline (basic), due to the release of hydroxide ions ($OH^-$).

Pre-Lab Q2: Formulas and Oxidation Numbers of Nitrogen Compounds

• Ammonia: $NH_3$ (Oxidation number of N: $-3$)
• Nitrous acid: $HNO_2$ (Oxidation number of N: $+3$)
• Nitrogen: $N_2$ (Oxidation number of N: $0$)
• Urea: $CO(NH_2)_2$ (Oxidation number of N: $-3$)
• Nitric acid: $HNO_3$ (Oxidation number of N: $+5$)

Pre-Lab Q3: Intermolecular Forces in Ammonia

• Strongest Intermolecular Force: Hydrogen bonding (between the lone pair on nitrogen and the hydrogen atom of an adjacent $NH_3$ molecule).
• Physical Consequences:
  • Unusually high boiling and melting points compared to other hydrides of group 15.
  • High solubility in polar solvents such as water.
  • High heat of vaporization.

Pre-Lab Q4: Reaction of Ammonia with Hydrochloric Acid and Release of Ammonia

• Reaction with HCl: $NH_3 + HCl \rightarrow NH_4Cl$ (Forms ammonium chloride).
• Releasing Ammonia: Treat $NH_4Cl$ with a strong base like sodium hydroxide ($NaOH$) and heat.
• Release Equation: $NH_4Cl + NaOH \rightarrow NH_3 + NaCl + H_2O$

Pre-Lab Q5: Identification and Properties of Ethylamine

• Compound Family: Primary aliphatic amine (Ethylamine).
• Functional Group: Amino group ($-NH_2$).
• Acid-Base Property: Weak base (the lone pair on nitrogen accepts a proton to form an ethylammonium ion).

Pre-Lab Q6: Electronic Structure and Physiological Effects of NO and NO2

• Common Electronic Feature: Both are free radicals containing an unpaired electron (odd-electron molecules).
• Physiological Effects:
  • NO (Nitric Oxide): Endogenous signaling molecule that acts as a potent vasodilator, regulating blood pressure and vascular tone.
  • NO2 (Nitrogen Dioxide): Toxic, lung-irritating gas that causes airway inflammation and pulmonary edema.

Pre-Lab Q7: Reaction of Nitrogen Dioxide with Water

• Reaction Equation: $3NO_2 + H_2O \rightarrow 2HNO_3 + NO$
• Environmental Importance: Key step in the atmospheric formation of acid rain ($HNO_3$) and photochemical smog.

Pre-Lab Q8: Mechanism of Action of Nitrate Esters (Nitroglycerol)

• Medical Use: Treatment of cardiovascular diseases such as angina pectoris.
• Mechanism of Action:
  • Nitroglycerol is biotransformed in vascular smooth muscle cells to release nitric oxide ($NO$).
  • $NO$ activates soluble guanylate cyclase, increasing intracellular cyclic GMP ($cGMP$).
  • Elevated $cGMP$ leads to vascular smooth muscle relaxation (vasodilation), reducing cardiac workload and improving myocardial perfusion.

Pre-Lab Q9: Reaction of P2O5 with 3 Moles of Water

• Reaction Equation: $P_2O_5 + 3H_2O \rightarrow 2H_3PO_4$
• Product Name: Orthophosphoric acid (phosphoric acid).

Pre-Lab Q10: Consecutive Dissociation of Orthophosphoric Acid

• Step 1: $H_3PO_4 + H_2O \rightleftharpoons H_2PO_4^- + H_3O^+$
• Step 2: $H_2PO_4^- + H_2O \rightleftharpoons HPO_4^{2-} + H_3O^+$
• Step 3: $HPO_4^{2-} + H_2O \rightleftharpoons PO_4^{3-} + H_3O^+$

Pre-Lab Q11: Pyrophosphoric Acid Formation and Hydrolysis Importance

• Formation Reaction: $2H_3PO_4 \rightarrow H_4P_2O_7 + H_2O$ (Condensation reaction with removal of water).
• Biological Importance of Hydrolysis: Hydrolysis of pyrophosphate ($PP_i$) bonds releases substantial free energy, driving endergonic biochemical processes forward and providing energy for metabolic pathways.

Pre-Lab Q12: Ester Formation of Phosphoric Acid with Methyl Alcohol

• Reaction: Reaction between phosphoric acid and methanol to yield monomethyl phosphate and water.
• Equation: $H_3PO_4 + CH_3OH \rightleftharpoons CH_3O\text{-}PO(OH)_2 + H_2O$

Pre-Lab Q13: Formulas of Inorganic Compounds

• Disodium hydrogenphosphate: $Na_2HPO_4$
• Fluoroapatite: $Ca_5(PO_4)_3F$
• Arsenic acid: $H_3AsO_4$
• Sodium bicarbonate: $NaHCO_3$
• Potassium cyanide: $KCN$

Pre-Lab Q14: Mechanism and Symptoms of Arsenic Poisoning

• Poisonous Mechanism: Arsenite ($As^{3+}$) binds strongly to sulfhydryl ($-SH$) groups of enzymes (such as pyruvate dehydrogenase), inhibiting cellular metabolism. Arsenate ($As^{5+}$) acts as a phosphate analog, uncoupling oxidative phosphorylation.
• Symptoms: Severe vomiting, watery diarrhea, garlic-like breath odor, abdominal pain, peripheral neuropathy, and cardiovascular instability.

Pre-Lab Q15: Activated Carbon and Its Medical Use

• Meaning: Form of carbon processed to possess a porous structure with an extremely large specific surface area.
• Medical Purpose: Administered orally as an emergency treatment for acute drug overdoses or poisoning.
• Why: Adsorbs toxins and chemicals in the gastrointestinal tract, preventing systemic absorption into the bloodstream.

Pre-Lab Q16: Oxides of Carbon Comparison

• Names & Formulas: Carbon monoxide ($CO$) and Carbon dioxide ($CO_2$).
• Physiological Effects:
  • $CO$: Highly toxic gas; binds hemoglobin with high affinity, preventing oxygen delivery to tissues.
  • $CO_2$: End product of respiration; regulates respiratory drive and blood pH.
• Reaction with Water:
  • $CO$: Unreactive with water under ambient conditions.
  • $CO_2$: Reacts reversibly to form carbonic acid: $CO_2 + H_2O \rightleftharpoons H_2CO_3$

Pre-Lab Q17: Preparation of Carbon Dioxide in Kipp's Apparatus

• Starting Materials: Calcium carbonate ($CaCO_3$, marble chips) and dilute hydrochloric acid ($HCl$).
• Reaction Equation: $CaCO_3 + 2HCl \rightarrow CaCl_2 + H_2O + CO_2$
• Utility: Allows controlled, intermittent gas generation at room temperature.

Pre-Lab Q18: Dissociation Equations and Mass Action Laws for Carbonic Acid

• Step 1: $H_2CO_3 + H_2O \rightleftharpoons HCO_3^- + H_3O^+$
  • $K_{a1} = \frac{[HCO_3^-][H_3O^+]}{[H_2CO_3]}$
• Step 2: $HCO_3^- + H_2O \rightleftharpoons CO_3^{2-} + H_3O^+$
  • $K_{a2} = \frac{[CO_3^{2-}][H_3O^+]}{[HCO_3^-]}$

Pre-Lab Q19: Reaction of Magnesium Carbonate with HCl and Medical Use

• Reaction Equation: $MgCO_3 + 2HCl \rightarrow MgCl_2 + H_2O + CO_2$
• Medical Use: Used as an antacid to neutralize excess stomach acid ($HCl$), relieving heartburn and acid indigestion.

Pre-Lab Q20: Carboxylic Acid Structure and Comparison with Carbonic Acid

• General Formula: $R\text{-}COOH$ (Functional group: Carboxyl group, $-COOH$).
• Comparison:
  • Carbonic acid ($H_2CO_3$): Unstable in aqueous solution, decomposing readily into $CO_2$ and $H_2O$ ($pK_{a1} \approx 6.35$).
  • Carboxylic acids ($R\text{-}COOH$): Thermodynamically stable in solution and generally stronger acids (e.g., acetic acid $pK_a \approx 4.76$) due to resonance stabilization of the carboxylate ion.

Pre-Lab Q21: Toxicity Mechanism of Carbon Monoxide

• Mechanism: $CO$ binds to the $Fe^{2+}$ center of hemoglobin with an affinity approximately 200–250 times greater than oxygen, forming carboxyhemoglobin ($COHb$).
• Effect: Impairs oxygen binding, shifts the oxygen-hemoglobin dissociation curve to the left, and causes severe systemic tissue hypoxia.

Pre-Lab Q22: Toxicity Mechanism of Cyanide Ion

• Mechanism: Cyanide ($CN^-$) binds tightly to the $Fe^{3+}$ ion of cytochrome c oxidase (Complex IV in the mitochondrial electron transport chain).
• Effect: Halts cellular respiration and ATP synthesis, leading to rapid cellular asphyxiation and organ failure.

Pre-Lab Q23: Acid Strength and Verification Reaction of Hydrogen Cyanide

• Acid Strength: Extremely weak acid ($pK_a \approx 9.21$), weaker than carbonic acid.
• Verification Reaction: Stronger acids displace $HCN$ from cyanide salts.
• Equation: $KCN + HCl \rightarrow KCl + HCN$

Pre-Lab Q24: Silicones: Structure, Properties, and Uses

• Structure: Synthetic polymers with a silicon-oxygen backbone ($\text{-}[Si(R)_2\text{-}O]_n\text{-}$) and organic side groups ($R$).
• Properties: High thermal stability, chemical inertness, water repellency, and biocompatibility.
• Uses: Sealants, lubricants, electrical insulation.
• Medical Uses: Medical implants, catheters, contact lenses, and scar treatment materials.