1. Not finding help here? Sign up for a free 30min tutor trial with Chegg Tutors
    Dismiss Notice
Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Chemistry Homework

  1. Jun 28, 2007 #1
    Hi, I am doing a chemistry course through correspondence and am not sure what they want me to answer for this question.

    The question states:

    Answer the following questions using the information in the table below.
    (Melting and boiling points are in Celsius)

    Element Melting Point Boiling Point Molar Volume STP
    A ====== -189 ====== -186 ====== 22.4 L

    B ====== -100 ====== -35 ====== 22.4 L

    C ====== -7 ====== 58 ====== 2.6*10-2

    D ====== 30 ====== 2240 ====== 1.2*10-2

    E ====== 44 ====== 280 ====== 1.7*10-2

    F ====== 660 ====== 2450 ====== 1.0*10-2

    G ====== 3410 ====== 5930 ====== 1.0*10-2

    Here are the questions with my answers so far:
    a)Which elements are likely to be metals?
    b)Which elements are gases at STP?
    For this I assume that elements A and B which have boiling points of less than 0 degrees celcius will be gases at STP.

    c) Which element is most likely to be a non-metallic solid?
    d) Which elements are liquid at 200 C?
    Well for this I think it would be D and E as they are the only elements with a melting point of less than 200 that have not yet turned into gases(unlike A,B, and C which are already gases before hitting 200)

    e) Which elements are likely to conduct well in the solid form?
    I think that it would be the metals but since I dont know A (which elements are metals) I cant actually know which elements those are.

    If someone could tell me if I got the ones I did right and explain to me how to find the others I would be very grateful.
     
  2. jcsd
  3. Jun 28, 2007 #2

    symbolipoint

    User Avatar
    Homework Helper
    Education Advisor
    Gold Member

    The very heaviest elements (highest molar volumes) are probably the metals. Maybe C and E are possibly the only ones, but I could be wrong in that some others may too be metals. The only gasses in the list are A and B which are also very light (see their molar volumes and note they boil at extremely low temperatures).

    You might try checking your answers in relation to the data from a handbook of physics and chemistry.
     
  4. Jun 28, 2007 #3
    I thought 22.4 L was bigger than 2.6*10 to the negative 2? When you do a negative power doesn't that mean that the decimal point moves to the right, making the number smaller?
    Also, do you have any ideas of how to find the answer to question c?
     
  5. Jun 28, 2007 #4

    symbolipoint

    User Avatar
    Homework Helper
    Education Advisor
    Gold Member

    The unit measurement values are "FOR A MOLE". A gas is of much lower density (much higher volume) than a solid.
    For question C, I'm really not sure, since some finer points of my descriptive elementary chemistry knowledge are now less than they used to be. Maybe someone else for this one....
     
  6. Jun 29, 2007 #5
    Thank you very much Symbolipoint. I did as you said and checked a table of boiling and melting points. It seems that the elements are (top to bottom) Argon, Chlorine, Bromine, Gallium, Phosporus, Aluminum, and Tungsten.

    Since only Argon and Chlorine are gases at STP I got question b correct. It would seem that high boiling points are related to metals because Gallium, Aluminum and Tungsten are all metals (d, f, and g). I saw that Phosphorus (e) is a non-metallic solid but I'm not sure how I was supposed to figure this out from the information given (although I believe it can be inferred through the fact that it has a relatively high molar volume but a low boiling point?). For finding the liquids I didn't gain any additional information so I still think it's d and e. For question e also I still think it is the metals.
    Thank you for all your help and clarification in this matter.:biggrin:
     
  7. Jun 29, 2007 #6
    the lesser the molar volume, the more likely the substance is a solid. what value is given to the standard temperature? using this you should be able to find out whether the substance will be a solid/liquid/gas at stp.
    what are the physical properties of typical metals? (there are metals which could be exceptions)
    you should also know the physical properties of non metals.

    i'll be giving you some hints:
    (a) metals are usually solids and usually have high m.p./b.p. (obvious exceptions are the Group 1 metals)

    (b) the boiling point should be less than the standard temperature for the substance to be a gas

    (c) non metals usually have low b.p./m.p. and here you have to take into account the molar volume since it is asking you for a solid.

    (d) you're right

    (e) you're right... the metals
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook

Have something to add?



Similar Discussions: Chemistry Homework
  1. Chemistry homework (Replies: 7)

  2. Chemistry Homework (Replies: 6)

  3. Chemistry Homework Help (Replies: 10)

  4. Chemistry homework (Replies: 8)

Loading...