Chm3120

chm3120
Download Document
Showing pages : 1 - 6 of 249
This preview has blurred sections. Sign up to view the full version! View Full Document
This is the end of the preview. Sign up to access the rest of the document.

Unformatted text preview: 1 Chapter 0 = The Analytical Process You should read this chapter. Chapter 1= Chemical Measurements Section 1-1: SI Units and Prefixes You should know this material. Section 1-2: Conversion Between Units You should know this material. Section 1-3: Chemical Concentrations Solution = solute + solvent Solute = minor species in solution. Solvent = major species in solution. Most common solvent in CHM 3120: water. Concentration = amount of solute contained in a given volume or mass of solvent. 2 Molarity (M) M is the number of moles of solute per liter of solution M = moles of solute / liters of solution moles of solute = weight of solute (g)/formula weight of solute (g) or moles of solute = mass of solute (g)/formula mass of solute (g) or moles of solute = mass of solute (g)/molecular mass of solute (g) Example: How many grams of Boric Acid [B(OH)3, FM 61.83] should be used to make 2.00 L of 0.0500M solution? moles of solute = 2.00 L x 0.0500M = 0.1 mol mass of solute = moles of solute x formula mass mass of solute = 0.1 mol x 61.83 g = 6.183 g Electrolyte An electrolyte dissociates into ions in aqueous solution. A strong electrolyte dissociates almost completely. Example: MgCl2 Mg+ + MgCl+ After dissociation, 89% exists in the form of Mg2+ and 11% in the form of MgCl+ The molarity of a strong electrolyte is referred to as Formal Concentration (F) to indicate that the substance is really converted into other species in solution. 3 A weak electrolyte is partially split into ions in solution. Example: Acetic Acid, CH3CO2H Note: If you dissolve 0.01000 mol of acetic acid in 1.000L, you will have: a 0.01000 F solution or a 0.00959M solution Why? because 4.1% is dissociated into CH3CO2- (acetate ion) and 95.9% remains as CH3CO2H. Nonetheless, we usually say that the solution is 0.01M and understand that some of the acid is dissociated 4 Molality (m) m is the number of moles of solute per kilogram of solvent (not solution!) The advantage of molality over molarity is that molality does not change with temperature. The molarity of a solution changes with temperature because the volume of solution changes with temperature. Percent Composition It is usually expressed as weight percent (wt%) wt% = [mass of solute / mass of total solution or mixture] x 100 Converting weight percent into molarity Example: Find the molarity of HCl in a reagent labeled 37.0 wt% HCl, density = 1.188g/mL. 37.0 wt% = There are 37.0 g of HCl in 100 g of reagent density = 1.188g/mL = allows us to calculate the volume of 100 g of reagent density (g/mL) = mass (g) / volume (mL) volume (mL) = mass (g) / density (g/mL) volume = 100 g / 1.188 g/mL = 84.1 mL 5 We know that: M = moles of solute / volume of solution in liters Moles of solute = mass of solute (g) / formula mass of solute (g) Formula mass of HCl = 36.46 g/mol Mass of solute = 37 g Volume of solution = 84.1 mL = 84.18 x 10-3 L Substituting these values ...
View Full Document