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Math Help - Stoichiometry/Conversions (Chem)

  1. #1
    TNB
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    Exclamation Stoichiometry/Conversions (Chem)

    How would I go about converting two moles of potassium bromide/KBr into grams? I got the answer of 171.42. (..grams?) Is this correct?

    Here's the original problem:
    What mass of Potassium Bromide is produced by the reaction of 2.65 moles of Calcium Bromide with excess potassium?

    Balanced Equation: 2K + CaBr2----> 2KBr + Ca
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  2. #2
    Junior Member JoanF's Avatar
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    Quote Originally Posted by TNB View Post
    How would I go about converting two moles of potassium bromide/KBr into grams? I got the answer of 171.42. (..grams?) Is this correct?

    Here's the original problem:
    What mass of Potassium Bromide is produced by the reaction of 2.65 moles of Calcium Bromide with excess potassium?

    Balanced Equation: 2K + CaBr2----> 2KBr + Ca
    Hi!



    Did you calculate it with the limiting reagent?
    You have to calculate the mass of the products using the limiting reagent because it is it which determines what happens on the reaction.
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  3. #3
    TNB
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    Umm, I'm in high school, and I've never heard of a limiting reagent. What is it? Your post says that it's infinity. As far as I know, inf+inf= inf., ect.

    Also, I clicked on your scratch sheet, but I cannot view it. What should I do so I can?
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  4. #4
    Junior Member JoanF's Avatar
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    Quote Originally Posted by TNB View Post
    Umm, I'm in high school, and I've never heard of a limiting reagent. What is it? Your post says that it's infinity. As far as I know, inf+inf= inf., ect.

    Also, I clicked on your scratch sheet, but I cannot view it. What should I do so I can?
    The infinity in my post is my signture.

    I don't know if you called limiting reagent to that I am refering.

    Check here: Limit Reagent

    Try here to view it: http://www.postimage.org/aV2tq0DJ-e9...e6fb68e840.jpg
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  5. #5
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    e^(i*pi)'s Avatar
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    Quote Originally Posted by TNB View Post
    How would I go about converting two moles of potassium bromide/KBr into grams? I got the answer of 171.42. (..grams?) Is this correct?

    Here's the original problem:
    What mass of Potassium Bromide is produced by the reaction of 2.65 moles of Calcium Bromide with excess potassium?

    Balanced Equation: 2K + CaBr2----> 2KBr + Ca
    It says that the potassium is in excess which means CaBr2 will be the limiting reagent.

    The standard way to solve these is:

    • Work out the number of moles of limiting reagent you have
    • Use the balanced equation to find out the ratio of moles used to moles produced
    • Multiply this value by the product in question's relative molecular mass to give mass in g


    In your case:

    1. You can skip this step as the mole number is in the question

    2. 1 mole of CaBr_2 will produce 2 moles of KBr.
    This means there are 2.65 \times 2 = 5.3 \text { moles KBr}

    3. KBr has a M_r of 80+39 =119g/mol

    Therefore there should be 119 \times 5.3 = 630.7g KBr formed
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  6. #6
    TNB
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    So the limiting reagent is the extra stuff that's not necessarily required for the reaction to take place..? I'm sorry, but I'm in general chemistry (non advanced placement) so I wasn't taught that. I'm not sure how they do it in your countries, Joan F/e^(i*pi). Is that taught in general chemistry where you live? And where are you guys from? I kinda recognize Pi's flag as that of Sweden, correct me if I'm wrong.. As for Joan, are you from.. India?

    Edit: Portugal? never would've guessed. Do you speak Portuguese? Now don't think I'm stupid or anything, it's just that you, for all I know, could've moved to Portugal from somewhere else. if so then.. Wow. foreign language(english/spanish??) instruction is so good in other countries! The USA really doesn't have a second language, officially. The "unofficial" 2nd language is pretty much Spanish, due to the influx of native speakers. And As for Pi.. You're form England? What's up with your flag? I thought the British flag was the Union Jack. Has it Changed? Or is that England's national flag, as opposed to the old "British Empire" one? I don't mean to insult you, I'm just used to the old "stars and bars".

    I'm really interested in foreign countries, having never left mine.. ever. It gets a bit sad looking at things from the same perspective all the time, not knowing what the rest of the world is doing. I need to watch the news.. But I'm a student. M'life is study study, get bored, slack off on internet, study.
    Last edited by TNB; April 22nd 2009 at 06:43 PM.
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  7. #7
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    e^(i*pi)'s Avatar
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    Quote Originally Posted by TNB View Post
    So the limiting reagent is the extra stuff that's not necessarily required for the reaction to take place..? I'm sorry, but I'm in general chemistry (non advanced placement) so I wasn't taught that. I'm not sure how they do it in your countries, Joan F/e^(i*pi). Is that taught in general chemistry where you live? And where are you guys from? I kinda recognize Pi's flag as that of Sweden, correct me if I'm wrong.. As for Joan, are you from.. India?

    Edit: Portugal? never would've guessed. Do you speak Portuguese? Now don't think I'm stupid or anything, it's just that you, for all I know, could've moved to Portugal from somewhere else. if so then.. Wow. foreign language(english/spanish??) instruction is so good in other countries! The USA really doesn't have a second language, officially. The "unofficial" 2nd language is pretty much Spanish, due to the influx of native speakers. And As for Pi.. You're form England? What's up with your flag? I thought the British flag was the Union Jack. Has it Changed? Or is that England's national flag, as opposed to the old "British Empire" one? I don't mean to insult you, I'm just used to the old "stars and bars".

    I'm really interested in foreign countries, having never left mine.. ever. It gets a bit sad looking at things from the same perspective all the time, not knowing what the rest of the world is doing. I need to watch the news.. But I'm a student. M'life is study study, get bored, slack off on internet, study.
    My flag is the English flag (St George's Cross) and today (23/4/09) happens to be St George's Day but no public holiday for us
    The Swedish flag is blue with a yellow cross if I recall correctly.

    I can't remember exactly but I believe the limiting reagent is touched upon in GCSE (which is what you get when leaving secondary school) but it is more explained in A Level.
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  8. #8
    Junior Member JoanF's Avatar
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    Quote Originally Posted by TNB View Post
    So the limiting reagent is the extra stuff that's not necessarily required for the reaction to take place..? I'm sorry, but I'm in general chemistry (non advanced placement) so I wasn't taught that. I'm not sure how they do it in your countries, Joan F/e^(i*pi). Is that taught in general chemistry where you live? And where are you guys from? I kinda recognize Pi's flag as that of Sweden, correct me if I'm wrong.. As for Joan, are you from.. India?

    Edit: Portugal? never would've guessed. Do you speak Portuguese? Now don't think I'm stupid or anything, it's just that you, for all I know, could've moved to Portugal from somewhere else. if so then.. Wow. foreign language(english/spanish??) instruction is so good in other countries! The USA really doesn't have a second language, officially. The "unofficial" 2nd language is pretty much Spanish, due to the influx of native speakers. And As for Pi.. You're form England? What's up with your flag? I thought the British flag was the Union Jack. Has it Changed? Or is that England's national flag, as opposed to the old "British Empire" one? I don't mean to insult you, I'm just used to the old "stars and bars".

    I'm really interested in foreign countries, having never left mine.. ever. It gets a bit sad looking at things from the same perspective all the time, not knowing what the rest of the world is doing. I need to watch the news.. But I'm a student. M'life is study study, get bored, slack off on internet, study.

    Yes, I am portuguese and I speak portuguese . Here we learn english when we are 10 years old and 2 years later we start to learn french by 3 years. When we are 15 years old we have to chose between english, french and german. I live in Portugal since my birth .

    (sorry for my english, by the way)
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