# Introduction to Chemical Concepts

*EXPRESSIONS OF SOLUTES:*

**MOLARITY**(M):- by definition, 1 mole per liter.
- Solvent is added and brought up to 1 L

**MOLALITY**(m):- by definition, 1 mole per kg of solvent
- for example, an aqueous solution with water, 1 kg of H
_{2}0 is approximately 1 L - 1mole is added to 1 kg of solvent

**NORMALITY**(N):- by definition, one equivalent per liter
- What is an equivalent?
- Molecular weight divided by the number of replaceable protons. For example, HCl there is one replaceable proton and therefore normality = molarity
- In contrast, H
_{2}SO_{4}or H_{3}PO_{4}have two and three replaceable protons, respectively. In the case of H_{2}SO_{4}, a 1 N solution would be equal to a 0.5 M solution.

- The advantage of normality is in titration, 1 equivalent of acid will completely normalize one equivalent of base.

**EQUILAVENTS**(Eq):- Electrolyte concentrations are expressed in milliequivalents (mEq)
- For single elements, an equivalent is the molecular weight divided by the absolute value of the oxidative state.
- Na
^{+1}: 23 gm = 1 Eq and 23 mg = 1 mEq - Cl
^{-1}: 35.5 gm = 1 Eq and 35.5 mg= 1 mEq - Ca
^{+2}: 20.0 gm = 1 Eq and 20 mg = 1 mEq

- Na
- For compounds, equivalents are calculated as the molecular weight divided by the absolute value of the highest oxidative state
- NaCl: 58.5 gm = 1 Eq NaCl
- CaCl
_{2}: 55.5 gm = 1 Eq CaCl_{2} - AlCl3: 44 gm = 1 Eq AlCl
_{2}

- Equivalent weights do not always remain the same since they result from the net electron change

**PERCENT COMPOSITION SOLUTIONS**- weight/weight (w/w)
- gm of solute per gm of solvent
- Example:
- 10% (w/w) NaOH: 10 gm of NaOH and 90 gm H
_{2}0

- 10% (w/w) NaOH: 10 gm of NaOH and 90 gm H

- weight/volume (w/v)
- Example:
- 10% (w/v) NaOH: 10 gm of NaOH dissolved in a small amount of solvent then brought up to 100 mL

- Example:
- volume/volume (v/v)
- Example:
- 30% Ethanol: 30 mL of 100% Ethanol and 70 mL H
_{2}0

- 30% Ethanol: 30 mL of 100% Ethanol and 70 mL H

- Example:

- weight/weight (w/w)
- CLINICAL EXAMPLES
- mg % = mg/dL = mg/100 mL

- TRACE METALS
- ppm (parts per million): mg / L
- ppb (parts per billion) µg / L