STPM化学专区

qwer0909

m／e的意示是mass／charge ratio。
mass在这里是指molecular weight（Mr）
charge就是ions的charge。 ...
四月一日的小皮 发表于 21-5-2010 02:21 PM

这个我大概懂了，那下面这个呢？

the mass spectrum of hydrogen chloride consists of 5 peaks at m/e values as shown in the table below. the heights of 2 peaks are also given. identify the ion responsible for each peak and calculate the relative molecular mass of hydrogen chloride.

m/e	relative abundance%	ion
1
35
36	37.5
37
38	12.5

四月一日的小皮

这个我大概懂了，那下面这个呢？

the mass spectrum of hydrogen chloride consists of 5 peaks at  ...
qwer0909 发表于 21-5-2010 09:45 PM

１=＞首先先确认ions。
m／e=１的peak是１H+（m／e=１／１）＊。
Cl有两个isotope，即Cl－３５和Cl－３７。
所以，m／e=３５的peak是３５Cl+ （ m／e= ３５／１）。
而m／e=３７的peak是３７Cl+（ m／e= ３７／１）。

２=＞relative molecular mass of hydrogen chloride
题目已经给了relative abundance （％）of HCl（即代表３６和３８的peak）。运用给予的提示找出来：

Mr（HCl） =[ ３６（３７.5) + 38(12.5) ] / (37.5 + 12.5)
          = 36.5

qwer0909

１=＞首先先确认ions。
m／e=１的peak是１H+（m／e=１／１）＊。
Cl有两个isotope，即Cl－３５和Cl－ ...
四月一日的小皮 发表于 21-5-2010 11:23 PM

那请问要怎样确认ions呢？是写HCl+ e-?这个我不会啊，你可以教我吗？拜托～

lokejiunnwoei92

各位大哥，教我这题，不明白
1.25g of gallium(Ga) to react with oxygen & obtain 1.68g of gallium oxide (Ga(x)O(y)).what is the formula of the product?

ELFofWAR

问一问
zomo chemistry有
organic ,inorganic 和pysical的？
我拿chem我就要读完上述三种？
还是单单读'chemistry'就够了？
(不要shoot我啊。。。我学校到现在都没有老师来。。。所以不懂==)

meiling

回复 608# ELFofWAR


中六chemistry就是physical, organic, inorganic组成的。。
你拿chemistyr就是必须读完这三本

四月一日的小皮

各位大哥，教我这题，不明白
1.25g of gallium(Ga) to react with oxygen & obtain 1.68g of gallium o ...
lokejiunnwoei92 发表于 22-5-2010 10:32 PM

let formula is:

xGa + (y/2) O2  ->  GaXOY

if 1.25g of Ga react fully/completely with O2,then:
mass of O= 1.68 - 1.25 = 0.43g

element:            Ga                     O
mass:               1.25g                0.43g
r.m.m:               69.7g/mol          16.0g/mol
mole:            (1.25/69.7)           (0.43/16)
                   = 0.0179 mol         =  0.0269 mol
ratio:         0.0179/0.0179          0.0269/0.0179
                   = 1                      =  1.5
                   = 2                      =  3
so, Gallium oxide = Ga2O3

四月一日的小皮

那请问要怎样确认ions呢？是写HCl+ e-?这个我不会啊，你可以教我吗？拜托～
qwer0909 发表于 22-5-2010 05:36 PM

在这里，homolysis of HCl存在。
radical of H和Cl会产生。

HCl －＞ H。 + Cl。

ion fragmentation的process是利用高速电子（eletron）来碰撞element／molecule to release它们的electron，方能产生unipositive
ions。（注：还可以产生+２，+３，...等等的ions，不过form６暂时没碰到。）

H。 + e－ －＞ H+  + ２e－
Cl。 + e－ －＞ Cl+ + ２e－

（以上在stpm很少会写到，不过请记住就是了。）

qwer0909

在这里，homolysis of HCl存在。
radical of H和Cl会产生。

HCl －＞ H。 + Cl。

ion fragmen ...
四月一日的小皮 发表于 22-5-2010 11:49 PM

也就是说只有h+和 Cl+吗？
那这题能解释给我听吗？
the mass spectrum of methane has 6 peaks of various m/e values as shown in the table below. identify the ion responsible for each peak and hence, write down the molecular mass of methane~

m/e	ion
1
12
13
14
15
16

lokejiunnwoei92

什么意思是找ions？？Example : how many ion are there in 42 g .......?

四月一日的小皮

也就是说只有h+和 Cl+吗？
那这题能解释给我听吗？
the mass spectrum of methane has 6 peaks of va ...
qwer0909 发表于 23-5-2010 12:23 AM

对，H+和Cl+。
要算m／e就用postive charge（like+１，+２...）
m/e   ions
1      H+
12    C+
13    HC+
14    H2C+
15    H3C+
16    H4C+(molecular ion)

什么意思是找ions？？Example : how many ion are there in 42 g .......?
lokejiunnwoei92 发表于 23-5-2010 09:14 AM

let say题目是：
How many ions in ４２g of sodium chloride（NaCl）？

１－＞找出mole of NaCl

r.m.m of NaCl = ( 23 + 35.5) = 58.5 g/ mol
mass of NaCl = 42 g
mole of NaCl = (42 / 58.5)  mol = 0.718 mol (3.s.f)

2 ->找出number of molecule／element／ions of NaCl

Avogadro constant = 6.02 x 10^23
1 mole of NaCl contains 1 mole of Na+ ions and 1 mole of Cl+ ios, since :
NaCl (aq) -> Na+(aq) + Cl-(aq)
that's mean,the total mole of ions in NaCl is 2 mole.
and yes, 0.718mole of NaCl contains 1.436 mole of ions.

no. of ions in NaCl
= mole of ions in NaCl x Avogadro constant
= 1.436 x 6.02 x 10^23
= 8.64 x 10^23

qwer0909

对，H+和Cl+。
要算m／e就用postive charge（like+１，+２...）
m/e   ions
1      H+
12    C+
13  ...
四月一日的小皮 发表于 23-5-2010 12:08 PM

erm...其实我不是要问答案，我是想问怎样找到～不好意思哦^^

qwer0909

rubidium, intensity=58mm, m/e85 n intensity 22.0mm, m/e 87
find
1)the relative abundance of the two isotopes
2)the relative atomic mass of rubidium

endless_story

我想问一题。。。
It was found that 4n atoms of metal X weighs 501.6 g. The relative atomic mass of X is 209. If n atoms of another metal Y weighs 65.00 g, what is the relative atomic mass of metal Y?

endless_story

谢谢解答咯。

四月一日的小皮

erm...其实我不是要问答案，我是想问怎样找到～不好意思哦^^
qwer0909 发表于 25-5-2010 09:25 PM

就是那么做咯，运用＃６１１的方法。

rubidium, intensity=58mm, m/e85 n intensity 22.0mm, m/e 87
find
1)the relative abundance of the t ...
qwer0909 发表于 25-5-2010 09:28 PM

1.m/e85 : { 58 / ( 58 + 22 ) }  x 100% =  72.5%
  m/e87 : { 22 / ( 58 + 22 ) } x 100% = 27.5%
2.r.m.m= { 85 ( 58 ) + 87 ( 22 ) } / ( 58 + 22 ) = 85.55
                                 or
  r.m.m=  { 85 ( 72.5 ) + 87 ( 27.5 ) } / ( 72.5 + 27.5 ) = 85.55

我想问一题。。。
It was found that 4n atoms of metal X weighs 501.6 g. The relative atomic mass of  ...
endless_story 发表于 26-5-2010 10:05 PM

１ －＞先找n：

mass of X = 501.6g
r.m.m of X = 209 g/mol

=>mole of X = 501.6/ 209 = 2.4 mol

no. of atom of X = 4 n
Avogadro constant = 6.02 x 10^23 /mol

=> 4 n = 2.4 x 6.02 x 10^23 atom
     n = 0.6 x 6.02 x 10^23 atom
     n = 3.612 x 10^23 atom

2 ->找Y咯！

no of atom in Y = n
                = 3.612 x 10^23 atom
=> mole of Y = 3.612 x 10^23 / 6.02 x 10^23
             = 0.6 mol

mass of Y in n atom = 65.00g

=> r.m.m of Y = 65 / 0.6 = 108.33 g/mol

endless_story

回复 619# 四月一日的小皮


    多谢了 厉害

silent91

请问
find the solubility of Pb(OH)2 in pure water?
given Ksp of PB(OH)2 is 1 X 10^-18 mol^3dm^-9

endless_story

请问∶
1) neon has 3 isotopes shown in the spectrometer. Ne-20 has a relative abundance of 90.9%. Ne-20 has a lower relative abundance than Ne-22. Find the relative abundance of Ne-20 and Ne-22 respectively, given the relative atomic mass of neon is 20.18.


2)The relative atomic mass of zinc is 65.37 and its density is 7.14 g/cm3. What is the volume of 1 atom of zinc? [Avogadro constant = L mol-1]

谢谢咯

四月一日的小皮

请问
find the solubility of Pb(OH)2 in pure water?
given Ksp of PB(OH)2 is 1 X 10^-18 mol^3dm^-9
silent91 发表于 28-5-2010 02:57 PM

solubility are in term of mol dm^-3.
Pb(OH)2 (s) -> Pb2+ (aq) + 2OH- (aq)
then, Ksp of Pb(OH)2 = [Pb2+][OH-]^2
let x is solubility.
then,Ksp of Pb(OH)2 = [x][2x]^2 = (x)(4x^2) = 4x^3
=> 1x10^-18 = 4x^3
then solve it using normal mathematics.

请问∶
1) neon has 3 isotopes shown in the spectrometer. Ne-20 has a relative abundance of 90.9%. N ...
endless_story 发表于 28-5-2010 08:45 PM

[quote]请问∶

1>>"neon has 3 isotopes shown in the spectrometer. Ne-20 has a relativeabundance of 90.9%. Ne-20 has a lower relative abundance than Ne-22.Find the relative abundance of Ne-20 and Ne-22 respectively, given therelative atomic mass of neon is 20.18."
i think that would be Ne-21.
let Ne-20:90.9%, Ne-21:x%, Ne-22:y%
x+y+90.9 = 100
       x+y = 9.1
          x = 9.1 - y    ............(1)

r.a.m of Ne = 20.18 = { 20(90.9) + 21(x) + 22(y) }  / 100
                   2018 = 1818 + 21x + 22y  ................(2)
(1)->(2):       2018 = 1818 + 21(9.1 - y) + 22y
                     200 = 191.1 - 21y + 22y
                     8.9  = y
=>                    x  = 9.1 - 8.9 = 0.2

2>> let mole of Zinc is M,r.a.m is Mr,Avogrado constant is L,mass of zinc is m....
mole of zinc,M = m/Mr.....(1)
mole of zinc,M = no. of atom (=1)/L
                 M = 1 / L  .....(2)

=>    m/ Mr = 1 /L

DENSITY, D            = m / V
             D            = Mr / (V x L )
   (D x L) / Mr        =  1  / V
             V           =  Mr / (D x L ) = 65.37 / 7.14L

the answer mayb in decimal form.