A soil sample with a OH- concentration of 10-9 M may also have high levels of aluminum.

Question

Answer the following statement true (T) or false (F)

Answer 1

True

Clarify Question
• What is the key concept addressed by the question?
        o This question is asking about the relationship between [OH-] and aluminum content of the soil.
• What type of thinking is required?
        o You are being asked to take what you already know and apply it to a specific soil condition.
• What key words does the question contain and what do they mean?
        o OH+ concentration, which can be used to calculate the pH of a substance.
        o Aluminum, which is a metallic element that can be toxic to many plants.
        o 1 x 10-9, which as a [OH+] can be converted into a pH value.

Gather Content
• What do you already know about the relationship between [OH-] and aluminum in the soil? How does it relate to the question?
        o Aluminum leaches into the soil from rocks if the soil is acidic.
        o pH =-log [H+]
        o [H+] + [OH-] = 1 x 10-14
        o Since we know that OH-= 1 x 10-9 in this soil, [H+] must equal 1 x 10-5
        o pH of this soil = -log (1 x 10-5), which equals -5, which equals 5
        o pH 5 means that this soil is acidic

Consider Possibilities
• What other information is related to the question? Which information is most useful?
        o Aluminum leaches into soil in acidic conditions.

Choose Answer
• Given what you now know, what information and/or problem solving approach is most likely to produce the correct answer?
       o Once you recognize that you can calculate pH from [H+], you can conclude that this soil is acidic. Aluminum enters the soil when the soil is acidic. Since the soil is acidic, it would have high levels of aluminum.

Reflect on Process
• Did your problem-solving process lead you to the correct answer? If not, where did the process break down or lead you astray? How can you revise your approach to produce a more desirable result?
• Apply level:
       o This question asked you to assess the likelihood of finding high aluminum concentration in a soil sample. Answering this question correctly depended on your ability to use the relationship between soil acidity and aluminum content in a new situation. If you got the correct answer, great job! If you got an incorrect answer, where did the process break down? Did you remember that aluminum content is higher in acidic soil, or pH can be calculated using [H+]? Did you have trouble extending the pH of the soil to determine the correct answer?