Understanding Concentration and Solution Expressions
Explore the concept of concentration in solutions and learn about different ways to express concentration measurements, such as percentages, molar concentrations, and more. Understand units of concentration and how to calculate parts per million and billion. Dive into the world of chemistry with detailed explanations and visual aids.
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Presentation Transcript
CONCENTRATION MEASUREMENT DR. KADR YE ZLEM HAMALO LU 10.12.2018
WHAT IS CONCENTRATION? A solution is a homogeneous mixture of one substance (the solute) dissolved in another substance (the solvent). Concentration is a ratio of the amount of solute to the amount of solution. File:SaltInWaterSolutionLiquid.jpg Concentration = quantity of solute quantity of solution (not solvent) DR. KADR YE ZLEM HAMALO LU 10.12.2018
CONCENTRATION There are 3 basic ways to express concentration: percentages, very low concentrations, molar concentrations % concentration can be in V/V, W/W, or W/V V/V and W/W need to have the same units on top and bottom. W/V is sort of in the same units; V is mostly water and water s density is 1 g/mL or 1 kg/L 1) 2) 3) DR. KADR YE ZLEM HAMALO LU 10.12.2018
SOLUTION AND CONCENTRATION Other ways of expressing concentration Molarity(M): moles solute / Liter solution Mass percent: (mass solute / mass of solution) * 100 Molality* (m) - moles solute / Kg solvent Mole Fraction(xA) - moles solute / total moles solution * Note that molality is the only concentration unit in which denominator contains only solvent information rather than solution. DR. KADR YE ZLEM HAMALO LU 10.12.2018
% CONCENTRATION mass solute % (w/w) = x 100 mass solution [ 3% w/w = 3 g/100 g] % (w/v) = mass solute volume solution x100 [ 3% w/v = 3 g/100 mL] volume solute x 100 % (v/v) = volume solution [ 3% v/v = 3 mL/100 mL] DR. KADR YE ZLEM HAMALO LU 10.12.2018
Units of Concentrations amount of solute per amount of solvent or solution g solute g solute x 100 x 100 = Percent (by mass) = g solution g solute + g solvent moles of solute volume in liters of solution Molarity (M) = moles = M x VL DR. KADR YE ZLEM HAMALO LU 10.12.2018
SOLUTION CONCENTRATION Expressing concentrations in parts per million (ppm) requires the unit on top to be 1,000,000 times smaller than the unit on the bottom E.g. 1 mg/kg or g/g Notice that any units expressed as a volume must be referring to a water solution (1L = 1kg)- density of water For parts per billion (ppb), the top unit would have to be 1,000,000,000 times smaller 1 ppm = 1 g/106 mL Cppm= m solution 1g = 1000mg 1000mg/1000L m solute x106 = 1 g/ 1000 L 1mg = 1000 g 1000 g/1000g = 1 mg/L DR. KADR YE ZLEM HAMALO LU 10.12.2018
MOLARITY C =n Molar concentration is the most commonly used in chemistry. amount of solute (in moles) Molar concentration = ----------------------------------------- volume of solution (in litres) V UNITS: ( mol/L) or (mol .L-1) or M DR. KADR YE ZLEM HAMALO LU 10.12.2018
CONCENTRATION: MIXED EXAMPLE A solution of H2O2 is 3% (w/v). a) Calculate the mass of H2O2 in 250.0 mL of solution. b) Calculate the mass of H2O2in 1L of solution. c) Calculate the number of moles of H2O2 in 1L of solution. d) State the molar concentration of the solution e) Calculate the ppm of H2O2 . DR. KADR YE ZLEM HAMALO LU 10.12.2018
CONCENTRATION: MIXED EXAMPLE-ANSWERS 3g mass = 250mL 100ml= 7.50g 3g 100ml=30g 34g= 0.88mol M = 0.88mol L Cppm= 100mL a) b) mass =1000mL n =30g1mol c) d) e) 3g x106=30000ppm DR. KADR YE ZLEM HAMALO LU 10.12.2018
HOW TO MEASURE CONCENTRATION???? Is there a device which measures the concentration of solutions????? DR. KADR YE ZLEM HAMALO LU 10.12.2018
