Solution Chemistry

Solution Chemistry. Solution chemistry deals with the study of solutions, which are homogeneous mixtures composed of a solute dissolved in a solvent.

Author: Hajira Mahmood

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Which water should I use?

• Tap water: Variable chemistry and purity
• Laboratory grade water: Reverse osmosis or distillation, Rinsing glassware, media preparation
• Reagent grade water: Filtration, deionization, and carbon adsorption
• Other specialized types: (dd, microfiltered, electrically deionized, etc)

Solution terminology

• Solution: A mixture in which individual molecules or ions are dispersed in a liquid.
• Solvent: The liquid that makes up the majority of the solution. e.g., water (aqueous solution).
• Solute: The minority component of the solution. Often a solid before mixing.

Measurements of concentration

These are amount of solute per volume of SOLUTION.

• Weight-per-volume (e.g., mg/L)
• Percent (parts per hundred)
• PPT, PPM, PPB
• Molar solutions

Weight-per-volume concentration

g/L, µg/mL, etc.

How to make up a 10 g/L aqueous solution?

• Weigh out 10 g of the substance.
• Put it in a vol. flask or grad. cylinder
• Add water up to the 1 L mark.

If you mix 1 L water with 10 g solute, then the total volume would be >1 L, and the concentration would be <10 g/L.

Percent (parts per hundred)

• w/w = grams per hundred grams total (this applies to compounds in solid materials, too)
• v/v = mL per hundred mL solution
• w/v = g per hundred mL solution
  

PPT, PPM, PPB

Like percent, except more dilute

• parts per thousand
• parts per million
• parts per billion

1 ppm = 1 µg/g = 1 µg/mL = 1 mg/L

Molar (M) solutions

Moles of solute per liter of solution

• 1 mole is 6×1023 molecules.
• The mass of 1 mole of a compound is the molecular weight (MW) of that compound.

Normal (N) solutions

The molarity of hydrogen ion equivalents produced by a compound in solution. (Usually applies to acids/bases.)

• For many chemicals the molarity and normality are the same
• 1M HCl is the same composition as 1N HCl Same for HNO₃ , HF, most organic acids (e.g. HCOOH)

Difference between molar and normal solutions

Occur when you are working with molecules with >1 exchangeable proton.

• Sulfate, phosphate, carbonate 18M sulfuric acid (H₂SO₄) is 36N
• There are 2 H+ ions (protons) per molecule
• Multiply the molarity of a solution by the number of H+ to get normality
• 5M phosphoric acid (H₃PO₄) is 15N

Dilution from one concentration to another

C₁V₁=C₂V₂

C₁ = initial concentration
V₁ = initial volume
C₂ = desired final concentration
V₂ = desired final volume

You need 100 ml of 1M NaCl and you have a stock solution of 5M NaCl

• What do you know?
• C1 = 5M
• C2 = 1M
• V2 = 100ml
• Answer … solve for V1 = C2V2/C1
• = 1M x 100 ml/5M = 20 ml of the stock

Special considerations for strong acids and bases

SAFETY: Whenever possible, add acid to water, not water to acid.

• Important primarily for very concentrated acids
• Prevents splashing & over-heating of acid

“Full-Strength” is not necessarily 100%

• Ex.: 100% HCl is a gas! The most concentrated liquid form is a 36% aqueous solution.
• So when diluting to make 10% HCl, you are starting from 36%, not 100%.

Also read: Project Planning and Delivery Lecture Presentation by Dr. Cornelia M. Wilson

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