chem lecture 6

chem lecture 6 - Water is a good solvent for many...

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Water is a good solvent for many substances. When ionic substances dissolve in water, their ionic lattices (arrangement of positive and negative ions in three dimensions) breaks down, and the individual ions attach on to the water molecules. This happens since water is polar (has a + and - end). Positive ions attach to the negative end of the water molecule, and negative ions attach to the positive end of the water molecule. This is called ion-dipole attraction, and will be discussed in more detail in later chapters. negative ion attached to positive ion attached to + end of water molecule - end of water molecule When ionic substances dissolve in water, the process is called dissociation. -Tap water conducts electricity better than distilled water because there are natural minerals (ions) which help to conduct electricity. -Our body is conducts electricity because we have natural ions on our skin sweat has NaCl EXAMPLES OF DISSOCIATION: NaCl(s) → Na + (aq) + Cl - (aq) MgCl 2 (s) → Mg 2+ (aq) + 2Cl - (aq) Na 2 SO 4 (s) → 2Na + (aq) + SO 4 2- (aq) Strong and Weak Electrolytes Strong electrolytes are solutions which are good conductors of electricity. Strong electrolytes are solutions which exist completely in the form of ions in aqueous solutions Ionic substances , such as in the dissociation examples above, are all strong electrolytes. Weak electrolytes are substances which are poor (but not zero) electrolytes. They are substances which partially convert into ions in aqueous solutions. However, most of the substance remains in molecular form. Most of the weak electrolytes that we will study are either weak acids or weak bases. Weak acids only partially produce H + ions in water, and weak bases only partially produce OH - ions in water.
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Strong and Weak Acids Acids are substances which produce H + ions in aqueous solution. Strong acids completely ionize in aqueous solution to produce H + ions and a negative ion The most important strong acids are hydrochloric acid, sulfuric acid, and nitric acid. All of these exist almost 100% as ions in aqueous solution. (good conducter of electricity) Hydrochloric acid HCl → H + (aq) + Cl - (aq) Sulfuric acid H 2 SO 4 → H + (aq) + HSO 4 - (aq) Nitric acid HNO 3 → H + (aq) + NO 3 - (aq) Weak acids only partially ionize into H + and negative ions. Acetic acid is an example of a weak electrolyte. CH
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This note was uploaded on 03/07/2012 for the course 830 201 taught by Professor Leyton during the Fall '08 term at Rutgers.

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chem lecture 6 - Water is a good solvent for many...

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