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Chapter 16: Q22P (page 392)

Why is iodine almost always used in a solution containing excess l-?

Short Answer

Expert verified

Iodine is always used in a solution with excess l- because purel2 is not a polar substance and it cannot be dissolved in water.

Step by step solution

01

Properties of Iodine.

  • Iodine is a chemical element with atomic number 53 and the symbol l .
  • At typical conditions, it exists as a semi-lustrous, non-metallic solid that melts to produce a deep violet liquid at 114掳C and boils to form a violet gas at 184掳C
  • Iodine is found in a variety of oxidation states, including iodideI- , iodate IO3-, and periodate anions.
  • It is the heaviest nutrient in terms of necessary minerals.
02

To determine the iodine always used in solution containing  

  • lodine is always used in a solution with excessI-because pureI2is not a polar substance and it cannot be dissolved in water.
  • Because of that, iodide solution(for example, Kl) must be added to iodine to increase its solubility,
  • The following reactions occurs:
  • I2(s)+I-(aq)鈬�I3-(aq)
  • In this reaction triodide is formed by a complexation reaction between iodide and iodine and the solubility of I2 is increased.

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Most popular questions from this chapter

Consider the titration in Figure 16-2.

(a) Write a balanced titration reaction.

(b) Write two different half-reactions for the indicator electrode.

(c) Write two different Nernst equations for the cell voltage.

(d) Calculate E at the following volumes of\(C{e^{4 + }}:10.0,25.0,49.0\), 50.0 .51 .0,60.0, and\(100.0\;mL\). Compare your results with Figure 16-2 .

(a) Potassium iodate solution was prepared by dissolving 1.022gof KIO3(FM214.00)in a 500 - mLvolumetric flask. Then 50.00mL of the solution were pipetted into a flask and treated with excess KI (2g) and acid (10mLof0.5MH2SO4) ofHow many moles of fl3- are created by the reaction?

(b) The triiodide from part (a) reacted with 37.66 mL of Na2S2O3solution. What is the concentration of the Na2S2O3 solution?

(c) A 1.223-g sample of solid containing ascorbic acid and inert ingredients was dissolved in dilute H2SO4 and treated with 2g of KI and 50.00mL of KIO3solution from part (a). Excess triiodide required14.22 mLofNa2S2O3solution from part (b). Find the weight percent of ascorbic acid (FM 176.13) in the unknown.

(d) Does it matter whether starch indicator is added at the beginning or near the end point in the titration in part (c)?

State two ways to make standard triiodide solution.

Consider the titration of 100.0mLof 0.0100MCe4+ in 1MHClO4by 0.0400MCu+ to give Ce3+ and Cu2+ , using Pt and saturated Ag | AgCl electrodes to find the end point.

(a) Write a balanced titration reaction.

(b) Write two different half-reactions for the indicator electrode.

(c) Write two different Nernst equations for the cell voltage.

(d) Calculate Eat the following volumes ofCu+:1.00,12.5,24.5,25.0,25.5,30.0 and 50.0 mL. Sketch the titration curve.

Some people have an allergic reaction to the food preservative sulfite (SO32-), which can be measured by instrumental methods 37 or by a redox titration: To 50.0mL of wine were added 50.0mL of solution containing (0.8043gKIO3+6.0gKI)/100mL . Acidification with 1.0 mL of 6.0MH2SO4 quantitatively converted role="math" localid="1663606948648" lO3 into l3 . The l3 reacted with SO32- to generate role="math" localid="1663607055826" SO42- , leaving excess l3 in solution. The excess l3 required of 12.86mLof0.04818MNa2S2O3to reach a starch end point.

(a) Write the reaction that occurs when H2SO4is added to KIO3+ KI and explain why 6.0 gKI were added to the stock solution. Is it necessary to measure out 6.0 g accurately? Is it necessary to measure 1.0 mL
ofH2SO4 accurately?

(b) Write a balanced reaction betweenl3 and sulfite.

(c) Find the concentration of sulfite in the wine. Express your answer in mol/L and inmgSO32- per liter.

(d) t test. Another wine was found to contain 277.7mgSO32-/Lwith a standard deviation of 卤2.2mg/Lfor three determinations by the iodimetric method. A spectrophotometric method gaverole="math" localid="1663607422230" 273.2卤2.1mg/L in three determinations. Are these results significantly different at the 95 % confidence level?
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