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Acids and Bases - Vinegar III

8th Grade Performance Task
Contributed by: RAND
Designed by: University of California, Santa Barbara, Stanford University, and The Far West Laboratory



1a 1 pt Orange
1b 1 pt Purple


2a 1 pt Color change in right direction: Purple to Blue to Green to Yellow to Orange to Red; Purple to Red; right to left on color guide; dark to light to dark / got lighter then darker; base to acid colors; colors go in opposite order on universal color guide.
Answers must include a start point color and an endpoint. (Not acceptable: Colors became lighter, darker, brighter, bolder, different, light to dark, or dark to light).
  1 pt Acidity change: base to acid; high to low pH; right to left on color guide; or solution neutralized and then turned to acid. Answers must include a start point (pH or base) and an endpoint (pH or acid).
    Note on 2a: If start point and endpoint are in different measures but are correct (e.g. solution went from Purple to Acid) give 1 point overall for 2a.
2b 1 pt 5
2c 1 pt Colors change faster; get to a specific color faster or with fewer drops; final color would be closer to red; fewer in between colors or skipped colors.
(Not acceptable: colors are different, brighter, lighter, darker, more intense, bolder; solutions are stronger or weaker; less colors or fewer colors.)
  1 pt Solutions would be more acidic; become acidic faster; the base will be neutralized quicker/with fewer drops of acid; solution balanced out quicker; end up with a strong or stronger acid.


3a 1 pt Acid C
3b 1 pt 9-20 drops or 1-12 drops more (must say more)
(Must get 3b correct to receive points for 3c)
3c 1 pt It takes more drop(s) to go from orange to red; 9 is orange red and 10 is red; the student bases their answer on a correct population.
  1 pt It takes more drops using Acid C to get the same outcome; Acid C causes a slower change than Acid B; Acid C is weaker or has higher pH than Acid B.

PART 4 (4d to 4f are to be scored separately)

  Line 1  
  1 pt 7 drops of Base X
  1 pt 2 drops of Acid B
  Line 2  
  1 pt 7 drops of Base X
  1 pt 6 drops of Acid C
4b 1 pt Acid B
(Must get 4b correct to receive points for 4c)
4c 1 pt Fewer drops of Acid B to get to neutral or to get to a specific color or to go from 1 color to another; Acid B changes colors more quickly; Acid B worked faster; Acid B got to a stronger acid color.


4di 1pt 3 vinegars used (may state 3 vinegars used or say each, every, all vinegars): or 2 vinegars (including the unknown) used. The unknown may be called the mystery vinegar or the third bottle.
4dii   These 2 points can be given regardless of validity of experiment
  1 pt Indicator used
  1 pt Base X use
4diii   These 2 points are only given if scorer can infer that the unknown vinegar is used. Inference rule is that student says more than 1 vinegar is being tested but does not indicate that only the 2 known vinegars are being tested.
    Also, these 2 points can be given (if the above inference met) if the student sets up a reversed experiment using a set amount of the vinegars and monitors drops of Base X added to the vinegars. Substitute vinegar for Base X and Base X for vinegar in the rubric to score this experiment for the following 2 points.
  1 pt Amount of Base X held constant in all tests
  1 pt The amount of vinegar added is monitored (Must use Base X to get this point)
4div 1 pt A comparison of the results from the different vinegars tested is made. The student must either say:
1. Compare the results of all three vinegars, or
2. Compare the results of the unknown vinegar (may be inferred unknown - see 4diii) with a specific known vinegar (either the 5% or the 6% vinegar). (The comparison must be of the color change to receive this point).
    Special Case for 4d (4 points possible)
  3 pt The answers says to follow the same steps as in Part 3 and notes that at least 2 vinegars are used (including the unknown vinegar) in place of Acids A & B.
(Must get all 5 points on 3a in Recipe or Discovery to get these points. If Text version can get all these points by referring to Tony's experiment as long as use of vinegar discussed).
  1 pt A comparison of the results from the different vinegars tested is made (see 4iv on the comparison).
4e 1 pt Base Z or yellow or the illustration of Base Z is circled.
(Give point if 4e left blank for 4f has Base Z).
4f 1 pt Yellow is less acidic or weaker than red; Red is more acidic or stronger than yellow. Takes more drops of Acid to make Base Z acidic; it is less acidic after the same number of drops added; harder to make Base Z an acid; less of a color change means a stronger base; Base Z did not weaker as much as Base Y: the higher pH number is a sign that Base Z is stronger: the resulting solution is closer to a base.
(Must get a point for 4e to receive this point)
  1 pt Number of drops of the bases and acids held constant for both tests (only needs to be said once).


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