2.3.Kf.FeSCN.by.Colormtry - Experiment THE FORMATION...

Info iconThis preview shows pages 1–3. Sign up to view the full content.

View Full Document Right Arrow Icon
1 Experiment THE FORMATION CONSTANT FOR A COMPLEX ION BY COLORIMETRY The CCLI Initiative Computers in Chemistry Laboratory Instruction LEARNING OBJECTIVES The objectives of this experiment are to . . . illustrate how colorimetric measurements are made using the MicroLAB interface. use Beer's Law to measure the equilibrium concentration of a complex ion. calculate the equilibrium constant for the formation of a complex ion. BACKGROUND Equilibrium When substances react, the concentrations of reactants and products change continuously until the system reaches chemical equilibrium. At equilibrium, no changes occur in the concentrations of any reactants or products as a function of time, as long as the system is not disturbed. Equilibrium occurs because chemical reactions are reversible. To illustrate this concept, consider the very important chemical reaction for the synthesis of ammonia from nitrogen and hydrogen: 2(g) 3 N + 3 H <==> 2 NH (g) (1) 22 3 The double arrows in this equation indicate that N and H not only can react to form NH , but that 3 NH can decompose to form N and H . When N and H react in a closed container, the 3 concentrations of these gases will initially decrease, and the concentration of NH will increase. As the concentrations of N and H decrease, fewer N and H collisions occur, so that the forward reaction 33 3 will slow down. At the same time, the increase in NH concentration results in more NH and NH collisions and the reverse reaction speed increases. Eventually the forward and reverse rates become equal, and no further changes occur in the concentrations of either reactants or products. The equilibrium constant One of the most striking properties of equilibrium is its consistency. For example, at equilibrium the concentrations of the substances in the ammonia synthesis reaction always obey the expression 3 K = [NH (2) [N ][H ] 2 where the square brackets indicate equilibrium concentrations in moles/liter. The equilibrium constant, K, is a constant for this reaction at a particular temperature. For example, at 500 C, the measured value of K
Background image of page 1

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
The CCLI Initiative 2 is 6.0 × 10 L /mol , which means that for this reaction system at 500 °C equilibrium will be achieved when -2 2 2 the concentrations are such that 3 [NH ] = 6.0 X 10 (3) -2 22 [N ][H ] 2 For a general reaction aA + bB <==> cC + dD (4) the equilibrium expression is written K = [C] [D] (5) cd [A] [B] ab where the bracketed capital letters represent concentrations of chemical species and the small letters represent the coefficients in the balanced equation. In this experiment you will study an equilibrium involving the formation of a complex ion, a species consisting of a metal ion with ligands attached to it. A ligand is a molecule or ion that has an electron pair that can be used to bond to an empty orbital on the metal ion.
Background image of page 2
Image of page 3
This is the end of the preview. Sign up to access the rest of the document.

This note was uploaded on 12/03/2011 for the course CHEM 2211 taught by Professor Facundofernandez during the Fall '09 term at Georgia Institute of Technology.

Page1 / 6

2.3.Kf.FeSCN.by.Colormtry - Experiment THE FORMATION...

This preview shows document pages 1 - 3. Sign up to view the full document.

View Full Document Right Arrow Icon
Ask a homework question - tutors are online