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Need help with (Acids and Bases) high school exam

  1. Dec 11, 2014 #1
    < Mentor Note -- thread moved to HH from the technical PF forums, so no HH Template is shown >

    Hello!

    So our teacher puts some really hard questions in acids and bases exams, and I would like someone to help me find similar questions and know how to solve these questions..

    So the first lessons were about acids and bases, and the lesson talked in general about acids and bases ( properties, arrhenius/bronsted lowry/lewis , acid ionization and base dissociation, naming acids , etc)

    But then in the exam he gave us some challenging questions :
    write the ionization reaction for the following compound :
    al(h2o)6 3+ ( weak acid)

    While solving the sample problems all the questions were pretty straightforward acids like HCl + H2O --> H3O+ + CL-

    but now i found this weird acid .... [ al(h2o)6 3+ ( weak acid) ]

    I searched online to find the answer and found it :

    Al (H2O)6 3+ <---double arrows---> Al(OH)(H2O)5 2+ and H+
    problem is, we usually solve with H3O+ not with H+... ( I know they're the same thing but I'm totally unfamiliar with the H+ thing...)

    can someone help with this question? how did we find the answer? and what are similar questions that can come like this ( hard acid/base ionization/dissociation problems like this)....



    Second challenging question :

    Geologist drops HCl on a rock , gas bubbles form. What might he conclude about the gas and rock ?

    gas: carbon dioxide rock : contains carbonate mineral?

    I didn't know these correct answers on the exam, but what are some similar problems to this one that can occur in the exam?

    and how can I study for the "harder" problems since the book's examples are too straightforward?
     
    Last edited by a moderator: Dec 11, 2014
  2. jcsd
  3. Dec 11, 2014 #2

    Borek

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    Staff: Mentor

    If you don't like the H+ alone just add water on the LHS, and you will get H3O+ on the right. After all, reaction takes place in water, so there is plenty of water molecules around.

    When it comes to the second question - how carbonates react with strong acids is just one of the things you have to remember.

    Sorry, can't help you with finding other problems, perhaps someone else will be able to chime in. Where do you live? I can offer you some insight about Polish books, but I doubt they will help you much ;)
     
  4. Dec 13, 2014 #3

    epenguin

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    Homework Helper
    Gold Member

    For your second question I think if you have to ask, then frankly your teaching is short-changing you, because if you had had a live demonstration you would never forget it. I hope it improves for you later. Chemistry just cannot be learned or appreciated from book and questionnaire alone. Pending improvement of the teaching, you should supplement it by looking online for demonstrations, like those cited below. Do this for all reactions you can. This is not as good as seeing directly or hands-on, but in compensation the sources are many and you can see them as many times as you want.

    Calcium Carbonate and Hydrochloric Acid Demo - YouTube


    Reaction of Calcium Carbonate with Hydrochloric Acid - YouTube


    Experiment 4.1 Investigating action of heat, water and acids on calcium carbonate


    I started to write about chemistry teaching in general, but it got too long and a bit of a rant, so maybe in another thread some other time soon.

    Edit by Borek: corrected videos for you :)
    Thx borek, ep:oldsmile:
     
    Last edited: Dec 13, 2014
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