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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