Molarity calculating

I Step 2 From the molarity, calculate the mass of solute in 1 L of solution. 

Notice that the numerator in molality calculations is the same as the numerator in molarity calculations, but that the denominators are different. For molality, the denominator differs in two respects It is in kilograms rather than liters and it involves solvent rather than solution. For the preparation of molal solutions, a volumetric flask is not needed. This is a preparation based only on weight. Molality is expressed in moles/kilo-gram. 

B) 0.100 M. This is a molarity calculation, which, if you recall, requires you to divide the moles of solute by the liters of solution. We already know that we have 50 mL of solution (or 0.050 L solution), so we just need the number of moles of Pb(N03)2 represented by 1.660 g ... 

The solubility of iodine in water is 0.00134 moles per liter. The apparent solubility of iodine in 0.007 molar KI (as determined from the concentration of titratable iodine) is 0.0048 molar. Calculate the apparent solubility of iodine in 0.10 molar KI. 

Example Radiation of wavelength 250 nm was passed through a cell containing 10 ml of a solution which was 0.05 molar in oxalic acid and 0.01 molar in uranyle sulphate. After absorption of 80 joules of radiation energy, the concentration of oxalic acid was reduced to 0.04 molar. Calculate the quantum yield for the photochemical decomposition of oxalic acid at the given wavelength. 

An approximately 0.1 molar solution of a silver salt in 1.0 molar ammonia is subjected to electrolysis for analytical purposes it is desired to reduce the concentration of the silver at least to 10 molar. Calculate the approximate initial and final potentials of the silver cathode. The instability constant of the Ag(NHs)J ion may be taken as 7 X 10 and the whole of the ammonia may be assumed to exist in the NH3 state. 

As with the molarity calculations, molality problems often incorporate the formula for determining the number of moles that a sample represents. Let s suppose you knew the mass of both the solute and the solvent that went into the solution. Would you be able to calculate the molality Here s an example. 

Stoichiometry concerns calculations based on balanced chemical equations, a topic that was presented in Chapter 8. Remember that the coefficients in the balanced equations indicate the number of moles of each reactant and product. Because many reactions take place in solution, and because the molarity of solutions relates to moles of solute and volumes, it is possible to extend stoichiometric calculations to reactions involving solutions of reactants and products. The calculations involving balanced equations are the same as those done in Chapter 8, but with the additional need to do some molarity calculations. Let s get our feet wet by working a couple of problems involving solutions in chemical reactions. 

While normality has been used extensively in the past and is found in the scientific literature, it is not as widely used today as molarity. We discuss normality in Section 5.6 for those who do make use of it. We will use moles and molarity throughout most of this text so there will be no ambiguity about what the concentration represents. Molarity calculations require a knowledge of the stoichiometry of reactions, that is, the ratio in which substances react. The journal Analytical Chemistry does not allow normality in articles it publishes, but other publications do. 

SOME USEFUL THINGS TO KNOW FOR MOLARITY CALCULATIONS... 

Many substances do not react on a 1 1 mole basis, and so solutions of equal molar concentration do not react on a 1 1 volume basis. By introducing the concepts of equivalents and nonnality, we can make calculations in these cases that are similar to molar calculations for 1 1 mole reactions. To do so, we define a new unit of concentration called normality. The symbol iV stands for normal, just as M stands for molar. The normality of a solution is equal to the number of equivalents of material per liter of solution ... 

Normality calculations are treated like 1 1 reactions in molarity calculations. 

Recall the last glass of water you drank. Although it seems unbelievable, that glass of water almost certainly contained water molecules that were also consumed by Albert Einstein, Joan of Arc, or Confucius Just how can two glasses of water poured at different times in history contain some of the same molecules Avogadro s number and molar calculations tell the story. 

Molarity calculated on the assumption of no volume changes on solution. 

Knowing where to start or what to do first is a critical part of working any math-type problem. This might be a factor if molarity calculations are difficnlt for you. First, of course, you must identify a problem as a molarity problem. This can be done by looking for a key word or phrase (molar, molarity, or moles/liter) or the abbreviation M. Second, remember that you have a formula for molarity... 

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