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Just a few IB chemistry exam questions... watch

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    So im in my first year of IB and am generally getting chemistry but theres a few types of questions im having trouble with... could someone help me out? Im doing a past paper so there should be a few...

    2. Which sample has the greatest mass?
    A. 6.02 x 10^23 molecules of hydrogen
    B. 5.0 mol of neon atoms
    C. 1.2 x 10^24 atoms of silver
    D. 1.7 x 10^2 g of iron

    4. Which sample of nitrogen gas, N2, contains the greatest number of nitrogen molecules?
    A. 1.4 g N2
    B. 1.4 dm^3 of N2 at 1.01 x 10^5 Pa and 273 K
    C. 1.4 x 10^23 N2 molecules
    D. 1.4 mol N2

    5. What is the atomic number of a neutral atom which has 91 neutrons and 40 electrons...
    The answer is 40, as its neutral so electrons must = protons correct?
    The other options are: 51, 91, 131


    .....

    That should be it for now. I really need to know the correct answers because im trying to make a markscheme for future use... but if you feel like explaining it quickly i would be thankful!
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    Hi there

    For the first question you should convert each option to mass using: (number of entities/avagadros number) x Mr of each individual entity, so for the first one 6.02 x 1023/6.02 x 1023 x 2 = 2g

    For the second question: its the reverse process of above, for B you will need the ideal gas equation too.

    Your answer to the last question is correct
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    Oh darn but sorry that doesnt help >.<. We haven't done this chapter so I really have no clue... do you think you could calculate each one so I can see? plzzzzz
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    I'm not inclined to do your homework for you :p:

    I've given you an example calculation for the question 2. Have a go yourself, I'll check your working

    For the second question you're trying to find the number of N2 molecules so for A: (number of molecules/avagadros number) x molecular mass of N2 = (n/6.02 x 1023) x 14 = 1.4g => rearranging gives n = 1.4/14 x 6.02 x 1023 = 6.02 x 1022 molecules. Try the others - B you need pV = nRT and D moles = mass/Mr

    Hope that helps
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    (Original post by ibjunk)
    Oh darn but sorry that doesnt help >.<. We haven't done this chapter so I really have no clue... do you think you could calculate each one so I can see? plzzzzz
    If you would like help with IB chemistry check out www.ibchem.com don't :woo:
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    Hey I just have a few more questions I can't seem to find the answer to anywhere. Can some one just look over my answers PLZ! I don't have chem for another week >.>

    Which statement best describes the intramolecular bonding in HCN?
    D. Electrostatic attraction between pairs of electrons and positively charged nucei

    Which molecule has the shortest bond between carbon atoms?
    C2H2 or C2H4Cl2

    I would think its C2H2 because of the triple bond, but it could be the other one!

    And lastly!
    Which of the following reactions are exothermic?
    I. CH4 + 2O2 --> CO2 + 2H2O
    II. NaOH + HCl --> NaCl + H2O
    III. Br2 --> 2Br

    There a multiple answers... I know that I. is exothermic... I know that II. is endothermic... but not sure about Br
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    (Original post by ibjunk)
    Hey I just have a few more questions I can't seem to find the answer to anywhere. Can some one just look over my answers PLZ! I don't have chem for another week >.>

    Which statement best describes the intramolecular bonding in HCN?
    D. Electrostatic attraction between pairs of electrons and positively charged nucei
    covalent bonds are considered electrostatic attractions between electron pairs and positive nuclear centres
    (Original post by ibjunk)
    Which molecule has the shortest bond between carbon atoms?
    C2H2 or C2H4Cl2
    I would think its C2H2 because of the triple bond, but it could be the other one!
    triple bonds are shorter than double bonds which are shorter than single bonds
    (Original post by ibjunk)
    And lastly!
    Which of the following reactions are exothermic?
    I. CH4 + 2O2 --> CO2 + 2H2O
    II. NaOH + HCl --> NaCl + H2O
    III. Br2 --> 2Br

    There a multiple answers... I know that I. is exothermic... I know that II. is endothermic... but not sure about Br
    I is combustion = always exo
    II is neutralisation = nearly always exo (there are exceptions, but this is not one of them)
    III is bond breaking = always endo
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    Going off my last question...

    CH4 + 2O2 --> CO2 + 2H2O

    Can this reaction occur during the incomplete combustion of methane... I know that C and CO are usually produced during incomplete, but couldn't some CO2 also be made???
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    (Original post by ibjunk)
    Going off my last question...

    CH4 + 2O2 --> CO2 + 2H2O

    Can this reaction occur during the incomplete combustion of methane... I know that C and CO are usually produced during incomplete, but couldn't some CO2 also be made???
    yes, incomplete just means that not all of the products are CO2 and H2O.
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    Oh thanks so much for your help I have just one last question then ill promise to leave you alone hahah!

    Which is a tertiary halogenalkane?
    A. CH3CH2CH2Br
    B. CH3CH2CH(CH3)Cl
    C. C(CH3)3Br
    D. CH3CHClCH2CH3


    PS. In regards to my other question... If it asked "what equations represented the incomplete combustion if methane"... and 3 equations were given...
    I. Producing CO2 + H2O
    II. Producing CO + H2O
    III. Producing C + H2O

    Would it be all 3... for some reason im still a bit unsure.
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    (Original post by ibjunk)
    Oh thanks so much for your help I have just one last question then ill promise to leave you alone hahah!

    Which is a tertiary halogenalkane?
    A. CH3CH2CH2Br
    B. CH3CH2CH(CH3)Cl
    C. C(CH3)3Br
    D. CH3CHClCH2CH3

    .
    Tertiary means that the halogen is attached to a carbon that has three carbon atoms attached.

    (Original post by ibjunk)
    PS. In regards to my other question... If it asked "what equations represented the incomplete combustion if methane"... and 3 equations were given...
    I. Producing CO2 + H2O
    II. Producing CO + H2O
    III. Producing C + H2O

    Would it be all 3... for some reason im still a bit unsure.
    I cannot represent incomplete combustion as there are no incomplete combustion products shown (either CO or C)
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    Ok these questions are tricking the hell out of me... I attached the originals as jpegs....

    For the kinetics question... I originally think that its all 3...

    Same for the combustion... but it seems WAY to easy for both of them to be all of the options!

    My exam is tomorrow and I have to know the correct answers!


    THANK YOU EVERYONE FOR YOUR HELP SO FAR... sorry for being such a bother
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    (Original post by ibjunk)
    Ok these questions are tricking the hell out of me... I attached the originals as jpegs....

    For the kinetics question... I originally think that its all 3...
    you, sure is.

    (Original post by ibjunk)
    Same for the combustion... but it seems WAY to easy for both of them to be all of the options!

    My exam is tomorrow and I have to know the correct answers!
    THANK YOU EVERYONE FOR YOUR HELP SO FAR... sorry for being such a bother
    Nope, 2 and 3 only
 
 
 
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