STPM化学专区

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.

silent91

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
四月一日的小皮 发表于 28-5-2010 10:22 PM

why concentration of OH- no need consider concentration of OH- in water???

四月一日的小皮

why concentration of OH- no need consider concentration of OH- in water???
silent91 发表于 29-5-2010 03:15 PM

remember that [Oh-][h+]= 10^-14???
in pure water, [oh-]=[h+]=10^-7=0.0000001
since it's value doesnt effect the [Oh-] of Pb(OH)2 as  X + 10^-7 = X.

silent91

remember that [Oh-][h+]= 10^-14???
in pure water, [oh-]=[h+]=10^-7=0.0000001
since it's value  ...
四月一日的小皮 发表于 29-5-2010 11:16 PM

  but after calculation, results of concentration of OH- is 10^-6
can consider near to 10^-7 woh~

qwer0909

a container 3.40g ammonia(NH3)gas.
how many moles of ammonia molecules are there?

天空之道

A 250cm3 of gaseous mixture of entane and ethene was reacted with bromine at stp.If 1.34g of bromine was used,determine the percentage of ethene in the mixture.(bromine:80)

四月一日的小皮

but after calculation, results of concentration of OH- is 10^-6
can consider near to 10^-7  ...
silent91 发表于 30-5-2010 02:54 PM

如过没记错的话，Pb（OH）２里的 ［OH－］是including pure water的
［OH－］。抱歉太久没看书了...xD

a container 3.40g ammonia(NH3)gas.
how many moles of ammonia molecules are there?
qwer0909 发表于 31-5-2010 10:03 PM

mass of ammonia gas = 3.40g
r.m.m of ammonia gas = 14 + 3 = 17 g/mol
mole of ammonia gas = 3.4 / 17 = 0.2 mol

???

A 250cm3 of gaseous mixture of entane and ethene was reacted with bromine at stp.If 1.34g of bromine ...
天空之道 发表于 31-5-2010 11:49 PM

remember...
1.when alkane will react with halogen to form haloalkane? Through which process? What is the conditions?
2.when alkene will reasct with halogen to form haloalkane? Through which process? What is the conditions?

My answer will just straight to the way to find answer.
let form equation 1st...
H2C=CH2 + Br2 -> Br-CH2CH2-Br

mass of Br2 = 1.34g
r.m.m of Br2 = 160 g/ mol
mole of Br2 = 1.34 / 160 = 8.375 x 10^-3 mol
In general,
1 mole of Br2 reacted with 1 mole of ethene to form 1mole of 1,2-dibromoethene.
Thus,
8.375x10^-3 mole with reacted with 8.375x10^-3 mole of ethene.
molar volume at s.t.p = 22400 cm^3 /mol
volume of ethene = 8.375 x 10^-3 x 22400 = 187.6 cm^3
then,
volume of ethane = 250 - 187.6 = 62.4 cm^3

percentage of ethene
= 187.6 / 250 x 100% = 75.04%

silent91

回复 629# 四月一日的小皮


没关系，你已经很厉害了～

qwer0909

argh,遮体不会啊～
a mixture containing 5.00g each of ch4, c2h4 and c4h10, is placed in a 1.50dm^3 flask at a temperature of 0 celcius.
A)calculate the partial pressure of each of the gases in the mixture
B)calculate the total pressure of the mixture
有人可以解释给我吗？谢谢哦～

四月一日的小皮

argh,遮体不会啊～
a mixture containing 5.00g each of ch4, c2h4 and c4h10, is placed in a 1.50dm^3 f ...
qwer0909 发表于 1-6-2010 08:48 PM

这一题需要运用到两个equation：
1.ideal gas equation。
2. dalton's law of independence.

1->运用ideal gas equation找出Pressure

PV=nRT
P= pressure in Pa
V= volume in m3
n= mole of molecule = m/ Mr
R= gas constant = 8.314 J K-1 mol-1
T= temperature in K

P= mRT/VMr
5.00g each of ch4, c2h4 and c4h10, is placed in a 1.50dm^3 flask at a temperature of 0 celcius.

P of CH4   = 5 ( 8.314 )( 0 + 273 ) / (1.5 x 10^-3)(12+4)
           = 5 ( 8.314 )( 273 ) / ( 16 )( 1.5x10^-3 )
           = 472.9kPa
P of C2H4  = 5 ( 8.314 )( 273 ) / (1.5x10^-3)( 28 )
           = 270.2kPa
P of C4H10 = 5 ( 8.314 )( 273 ) / (1.5x10^-3)( 58 )
           = 130.4kPa

2->=加起来咯！

Total P = ( 472.9 + 270.2 + 130.4 )kPa
        = 8.74 x 10^2 kPa

endless_story

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

这边不是很明白为什么density会等于 Mr/ (V x L)  ?

四月一日的小皮

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 = ...
endless_story 发表于 2-6-2010 04:32 PM

就是运用
m／Mr = １／L
m = Mr／L .....(1)

D = m /V ..... (2)

(1)->(2): D = (1 / V)(Mr / L )

qwer0909

这一题需要运用到两个equation：
1.ideal gas equation。
2. dalton's law of independence.

1->运 ...
四月一日的小皮 发表于 1-6-2010 11:27 PM

恩，这个会来，谢谢哦～

qwer0909

这题好难啊，可以教我吗?
bromine consists of two isotopes 79br and 81br, with relative abundance 50.5% and 49.5% respectively.Apart frm the peaks at 79 and 81 , due to br+ ions frm these two isotopes, the mass spectrum of bromine also shows peaks at 158, 160, and 162.
a)what are the ions that gives rise to these three peaks in the spectrum of bromine?(这题我会）
b)the relative heights of these three peaks are in the ratio 1:2:1.can you explain this ratio, taking into account your answer to part(a) and the information about the relative abundance of the two bromine isotopes?

b的我不会啊，你可以帮我解释吗？谢谢～

四月一日的小皮

这题好难啊，可以教我吗?
bromine consists of two isotopes 79br and 81br, with relative abundance 50. ...
qwer0909 发表于 3-6-2010 09:17 PM

158 => 79br-79br
160 => 79br-81br and 81br-79br
162 => 81br-81br

relative abundance calculation:
                        158                           160                           162  
                (0.505)(0.505)            2(0.505)(0.495)             (0.495)(0.495)
                = 0.255                      = 0.500                        = 0.245
ratio       0.255/0.245 = 1.04         0.500/0.245 = 2.04         0.245/0.245 = 1
                              = 1                              = 2                              = 1

lokejiunnwoei92

这边有两题题目我做到答案，但小数点不对。
1.What is the density (gdm-3)of propane,C3H8,at s.t.p?
My Solution:M/V=1.01x10^5 x ((44/(8.31)(273))
                       =1958.9....duno wht unit bt the ans given is 1.96gdm-3
2.The density of a gas at 25C & 1.05x10^5 Pa is 1.19gdm-3.Calculate the relativemolecular mass of the gas??
  The ans given is 28.1 but i calculate get 0.028,me also duno my decimal where got problem.Help me anyone

四月一日的小皮

这边有两题题目我做到答案，但小数点不对。
1.What is the density (gdm-3)of propane,C3H8,at s.t.p?
My ...
lokejiunnwoei92 发表于 5-6-2010 12:32 AM

你的R是８.31JK-1mol-1,
是８.31 m3  Pa K−1 mol−1 ...

你应该用０.0821 L atm K-1 mol-1,
就是0.0821 dm3 atm K-1 mol-1.

１－＞题目要求你找g dm－３，不是g m－３。
２－＞题目已经给你density in g dm－３，你就应该用R=０.0821.

请记住，unit很重要。

白精灵74

我想问关于mass spectrum 的东西，
像chlorine gas 在mass spectrum 里面,
question is how many TYPES of molecules can be found in d mass spectrum?
学校老师告诉我3个，补习老师告诉我4个。