Assume that you want to construct a voltaic cell that uses the following half-reactions:

\(\mathrm{A}^{2+}(a q)+2 \mathrm{e}^{-} \longrightarrow \mathrm{A}(s) \quad E_{\text {red }}^{\circ}=-0.10 \mathrm{~V}\)

\(\mathrm{B}^{2+}(a q)+2 \mathrm{e}^{-} \longrightarrow \mathrm{B}(s) \quad E_{\mathrm{red}}^{\circ}=-1.10 \mathrm{~V}\)

You begin with the incomplete cell pictured here in which the electrodes are immersed in water.

(a) What additions must you make to the cell for it to generate a standard emf?

(b) Which electrode functions as the cathode?

(c) Which direction do electrons move through the external circuit?

(d) What voltage will the cell generate under standard conditions? [Sections 20.3 and 20.4]

Text Transcription:

{A}^{2+}(a q)+2 {e}^{-} \longrightarrow {A}(s) \quad E_red }}^{\circ}=-0.10 V

{B}^{2+}(a q)+2 {e}^{-} \longrightarrow {B}(s) \quad E_{red}}^{\circ}=-1.10 V

1 Chapter 3 The Mole and Stoichiomtery Objectives: Avogadro's number Moles Percent Composition of Compounds Empirical Formula Stoichiometry Limiting Reagent Reaction Yield A dime weighs 2.27 g. The mass of a bag of dimes is 227 g. How many dimes are in the bag How do you determine the chemical formula of a substance How much of Y can you prepare from a given quantity of X X (aq) Y (aq) Molecular Weight and Formula Weight: Molecular weight is the sum of the atomic weights of all atoms in a molecule. Ex: What is the molecular weight of H O 2 2 34.0147 g/mol The formula weight (FW) of a substance is the sum of the atomic weights of all atoms in a formula unit of the compound whether molecular or not. Ex: What is the formula weight of H S2 4 98.079 g/mol Moles: 2 Mole (mol) Latin, a large number A very important unit in chemistry A 10.0 g sample of ethanol (<3 teaspoons) contains: 131,000,000,000,000,000,000,000 molecules. It is not very easy to count all these molecules! One mole is defined as the number of atoms in exactly 12 g of C12 atoms. 1 mole Na = 23.00 g Na Mole concept to deal w/ the number of molecules. mole = mass molecular weight One mole of NH c3ntains 17.04g of the molecule. Avogadro's Number: A special unit to describe a very l