Question 50 of the Spring 2003, Grade 10, Texas Assessment of Knowledge and Skills (TAKS) released Science test reads as follows:

                                                     Solubility Rules
                  ---------------------------------------------------------------------------------------
                    1. All sodium, potassium, and ammonium salts are soluble.
                    2. All silver, lead, and mercury salts are insoluble.
                    3. All carbonates, sulfides, and hydroxides are insoluble.
                    4. All sulfates are soluble except calcium sulfate and barium sulfate.
                  ---------------------------------------------------------------------------------------

            50   Which of the following salts has the greater solubility in water at 25oC?

                    F   CaCO3
                    G   FeS
                    H   HgCl2
                    J   KClO4

      Out of the 245089 students who took the test, the response percentages for answers F, G, H, J, and no answer were, respectively, 19%, 21%, 17%, 43%, and 0%.

Scoring mistake
      Answer H, HgCl2, is the only correct answer.  Answers F, G, and J are incorrect.  The Texas Education Agency gave credit for the incorrect answer J and made the mistake of denying credit for the correct answer H.  The TEA wrongly decreased the scores of those roughly (17%)(245089) = 41665 students who chose answer H.  The remedy for this mistake is to give credit for answer H.
      The TEA also made the mistake of providing solubility rules to which the correct answer, HgCl2, is an exception, but of not providing students, who were not expected to have detailed knowledge of solubilities, an opportunity to check for exceptions.

Details
      The solubility of mercuric chloride, HgCl2, in water at 25oC is more than twice that of the next most soluble compound, potassium perchlorate, KClO4.  According to a U. S. Environmental Protection Agency report,* the solubility of HgCl2 in water is about 70 g/L at 25 C.  According to this solubility curve,** the solubility of KClO4 in 100 g of water is about 3 g at 25oC.  The solubility of HgCl2 in water is also greater than that of KClO4 at other temperatures from 0oC to 100oC.***
      The correct answer, HgCl2, is an exception to the given solubility rule 2.  Since tenth graders are not expected to have detailed knowledge of solubilities and were not given an opportunity to check for exceptions to the given solubility rules, it is undoubtedly true that solubility rule 2 unduly mislead some students away from the correct answer H, HgCl2.
____________________
    *   EPA-600/R-01-066, September 2001, pages 25 and 29.
  **   A roughly similar solubility curve for KClO4 is shown in Table 13-3 on page 451 of Linus Pauling, General Chemistry, Dover, New York 1988 (W. H. Freeman and Company, San Francisco 1970), ISBN: 0486656225.
***   According to this ILO listing, the solubility of HgCl2 in 100 ml of water is 7.4 g at 20oC.  According to this ILO listing, the solubility of KClO4 in 100 ml of water is 1.8 g at 20oC.
      According to http://chemdat.merck.de/cdrl/services/labtools/en/table_solinl.html, the solubility of HgCl2 in 100 g of water is 4.29 g at 0oC, is 6.6 g at 20oC, is 9.6 g at 40oC, is 13.9 g at 60oC, is 24.2 g at 80oC, and is 54.1 g at 100oC.  According to http://chemdat.merck.de/cdrl/services/labtools/en/table_solinp.html, the solubility of KClO4 in 100 g of water is 0.76 g at 0oC, is 1.7 g at 20oC, is 3.6 g at 40oC, is 7.2 g at 60oC, is 13.4 g at 80oC, and is 22.2 g at 100oC.
      According to the CRC Handbook of Chemistry and Physics, 59th Edition, Robert C. Weast, Editor, CRC PRESS, Inc., West Palm Beach, Florida 1978, ISBN: 0849305498, the solubility of HgCl2 in 100 cc of water is 6.9 g at 20oC and is 48 g at 100oC (page B-137) and the solubility of KClO4 in 100 cc of water is 0.75 g at 0oC and is 21.8 g at 100oC (page B-149).

Failure to correct the scoring mistake
      The Texas Education Agency was informed of the mistake before 4 August 2003.  On 4 August 2003, the TEA issued the response TAKS Released Test Items and issued, in "Additional Information Regarding Released Science Items", the statements

      Item 50 asked students to apply a list of solubility rules to a compound.  This item
      was intended to measure the IPC TEKS 9(D), which required students to
      demonstrate how various factors affect solubility.  The general solubility rules as
      they appeared in the item were written specifically for this item and were not
      intended to be used for ongoing instruction.  Some of the compound types listed
      in rules 2 and 3 are soluble.  This item has only one answer that could be correct
      and is a valid question for all students tested at this level.

      The TEA states that "However, upon review, these items were determined to be correct and no action was taken by the agency."  This TEA statement refers to questions that include question 50.  By "determined to be correct" the TEA means that answer J is correct and that answer H is incorrect.  The TEA's claim that answer J is correct is false.  The TEA's claim that answer H is incorrect is false.
      The TEA states that "Item 50 asked students to apply a list of solubility rules to a compound."  This TEA statement is inaccurate; question 50 asks "Which of the following salts has the greater solubility in water at 25oC?"
      The TEA states that "This item was intended to measure the IPC TEKS 9(D), which required students to demonstrate how various factors affect solubility."  Application of the given solubility rules to the listed compounds requires some knowledge of chemical nomenclature but does not require any knowledge of factors that affect solubility or even that students know the meaning of solubility.
      The TEA states that "The general solubility rules as they appeared in the item were written specifically for this item and were not intended to be used for ongoing instruction."  The TEA knows that students, teachers, and others may study and learn from questions on released TAKS tests, including question 50, and may be mislead be the fact that the TEA's answer key is incorrect.
      The TEA states that "Some of the compound types listed in rules 2 and 3 are soluble."  This TEA statement does not acknowledge the fact that the correct answer, HgCl2, is an exception to the given solubility rule 2.  Competent chemistry assessment experts are aware that solubility rules, especially make-believe solubility rules, may be liable to exceptions and would have checked for exceptions to eliminate the possibility that they might unduly mislead students away from the correct answer, HgCl2.  In General Chemistry (see footnote above), Linus Pauling states that "All chlorides, bromides, and iodides are soluble except those of silver, mercurous mercury (mercury with oxidation number +1), and lead" (page 453) and that "Mercuric chloride, like other soluble salts of mercury, is very poisonous when taken internally" (page 718).  Mercury has oxidation number +1 in mercurous chloride, Hg2Cl2, and oxidation number +2 in mercuric chloride, HgCl2.  Pauling also states that "Nearly all the perchlorates are highly soluble in water; potassium perchlorate is exceptional for its low solubility, 0.75 g in 100 g of water at 0oC" (page 263).
      The TEA states that "This item has only one answer that could be correct and is a valid question for all students tested at this level."  By "only one answer that could be correct", the TEA means that answer J is correct and that the other answers, including answer H, are incorrect.  The TEA's claim that answer J is correct is false.  The TEA's claim that answer H is incorrect is false.
      The TEA's false claims are due to incompetence or dishonesty.  Texans are ill-served by such incompetence or dishonesty.

      The TEA has continued to propagate the scoring mistakes and false claims without correction.
      On 15 July 2005, Mark Loewe gave written and oral testimony to the State Board of Education on the topic "TEA failed to correct TAKS mistakes".  The SBOE has failed to acknowledge or to correct any of the TEA's scoring mistakes or false claims.