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Stoichiometry Unit Exam in 2 Days?!? I'm crying help!


Andy K.

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Hello IB folks,

I will go straight into my topic. So, my stoichiometry unit exam is in 2 days... (Im grade 11 btw) and I am so stuck on some of these questions....:?

I am very much familiar with the sub topics (molar masses/conversions/solution/dilution/etc.), but when it comes to actual stoiciometry word problems, I am just stumped...

I find it so hard to solve them because often times, I don't know where to start or the approach to the questions...(although not all of them...)

I am sitting here with a batch of sample word problems, and they are just so hard to get by because they are worded all differently...

And most of all, Im so scared because this is my first big chem test and the past averages for this test were 60% in the past years!

I would like to seek help mainly on steps or procedures(if there are any...) to solving these word problems from you friends:hisfault:

Any helpful tips or experiences with this unit would be greatly appreciated as well. 

It's not that I don't know the concepts, but I am having a hard time with the approach.

Thank you very much all! :gbye:

 

 

Edited by Andy K.
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You will come to find out that stoichiometry will probably the simplest conceptual unit in IB Chemistry, especially if you're in HL.

Stick to textbook and practice questions. Follow the process, use unit conversions (they really help), and just make sure you read the question right. It's basically all quantitative so there's no real understanding involved, just practice. YouTube is a wonderful resource if you really need someone providing explanations.

Good luck!

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The idea with stoichiometry is essentially to compare different amounts of different substances. If you begin with grams of a substance and need grams of another, for example, find out how many grams per mole and make that a fraction to cancel grams by multiplying by the amount of grams you began with, then find out how many moles of one substance exist in proportion to the other (the coefficients in the equation, basically) and cancel moles of the substance you began with, then multiply by the grams of your new substance per mole of that substance.

The idea basically is this: mass of B = [(mass of A)] x [(moles of A)/(mass of A)] x [(moles of A)/(moles of B)] x [(mass of B)/(moles of B)], and you begin or end anywhere in this depending on whether you begin with mass of moles and want to end with mass or moles.

Essentially, cancel out units until you have the unit you want, in this case, the number of moles of the new substance.

Feel free to ask if you want further clarification or if you want to go through an example.

Hope this helps!

Edited by mushroom
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