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The Mole and Avogadro’s Number (Chapter 3, Section 1)

The Mole and Avogadro’s Number (Chapter 3, Section 1). A mole (abbreviated “mol”) is “the amount of substance that contains the same number of entities as there are atoms in exactly 12g of Carbon-12.” 1 mole contains 6.022 x 10 23 entities (6.022 x 10 23 is Avogadro’s number, N A ).

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The Mole and Avogadro’s Number (Chapter 3, Section 1)

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  1. The Mole and Avogadro’s Number (Chapter 3, Section 1) A mole (abbreviated “mol”) is “the amount of substance that contains the same number of entities as there are atoms in exactly 12g of Carbon-12.” 1 mole contains 6.022 x 1023 entities (6.022 x 1023 is Avogadro’s number, NA) How many molecules are in 2.5 moles of Nitrogen gas? Avogadro’s number can be used as a conversion factor! Note that the numeric coefficients in a balanced equation (the equation’s stoichiometry) are often referred to in units of moles, not just numbers of molecules.

  2. Problem 3.15(a) Calculate the total number of ions in 38.1g of SrF2

  3. Limiting Reagents(Chapter 3, Section 4) It is not always the case that we have enough of all of our reactants to react completely according to the stoichiometry of an equation to give products. Sometimes, there isn’t enough of one of the reactants to react with all of the other reactant present. In this case we say that one of the reactants is the limiting reactant (that is, it will be completely used up and limit the extent to which the reaction occurs) The other reactant will be present in excess (that is, there will be some of this reactant left over when the reaction stops.)

  4. Problem 3.76 Calculate the maximum numbers of moles and grams of H2S that can form when 158g of aluminum sulfide reacts with 131g of water: Al2S3 + H2O  Al(OH)3 + H2S (unbalanced) What mass of the excess reagent remains?

  5. Concentration(Chapter 3, Section 5) Concentration is how we express the amount of something per unit volume In a solution, the substance that is present in a smaller amount is called the solute. The solute is dissolved in the substance that is present in a larger amount, called the solvent. Most common concentration unit you will encounter is Molarity (M) Molarity is moles solute per liters of solution: Note that molarity involves the liters of solution (which includes the volume of both the solvent and the solute)

  6. Dilution(Chapter 3, Section 5) A common way to prepare a solution is to start with a more concentrated stock solution and dilute it to form a less concentrated working solution. The principal behind dilution is that the concentration changes because the volume of the solution is changing – the moles of solute stays the same. This principle is illustrated by the following useful equation: M1V1 = M2V2 Where M1 is the concentration (in molarity) of the more concentration solution and V1 is the volume of the more concentrated solution, M2 is the concentration (in molarity) of the less concentrated (the dilute) solution and V2 is the volume of the dilute solution. (Note that the volumes in this equation need not be in units of Liters, as long as both V1 and V2 are in the same volume units.)

  7. Problem 3.125 (d) Calculate the mass of calcium nitrate in each milliliter of a solution prepared by diluting 64.0 mL of 0.745 M calcium nitrate to a final volume of 0.100 L.

  8. pHChapter 18 and Chapter 4 Little “p” means “Take the –log of” whatever follows it To calculate pH you take the –log of the concentration of H+ (or H3O+) in solution pH scale is a logarithmic scale from 1-14 (working range) pH below 7 is acidic, above 7 is basic and 7 is neutral There are negative pH values and pH values above 14. You should know the six strong acids (acids that completely dissociate in water to give H+ (H3O+) in solution) and five strong bases (bases that completely dissociate in water to give OH- in solution) that are listed in Table 4.2 on page 151 of Chapter 4.

  9. Problems 18.24(a and b) and 18.28(a) What is the pH of 0.0333 M HNO3? Is the solution neutral, acidic or basic? What is the pOH of 0.0347 M KOH? Is the solution neutral, acidic or basic? What are [H3O+], [OH-], and pOH in a solution with a pH of 3.47?

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