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kensai

1) no of mol of compound = 12.4/128= 0.05 mol

1 mol of sodium thiosulphate give 2 mol of Na
so, 0.05 mol of sodium thiosulphate give 0.1 mol of NA

concentration of NA solution = 0.1 moldm^-3

2) 问题很模糊，可以看看有打漏吗？

potassium chlorate(V) is heated strongly,it decomposes into potassium chlorate(VII),KCLO4,and potassium chlorat

从 kclo3 -> KClO4 + pottassium chlorate, 最后那个 potassium chlorate 的 oxidation state 是多少呢？有写吗？
还是只是 KClO3 -> KClO4 罢了？

原帖由 kensai 于 20/5/2006 23:07 发表
1) no of mol of compound = 12.4/128= 0.05 mol

1 mol of sodium thiosulphate give 2 mol of Na
so, 0.05 mol of sodium thiosulphate give 0.1 mol of NA

concentration of NA solution = 0.1 moldm^-3 ...

i tell u question again la
when potassium chorate(V) is heated strongly,it decomposes into potassium chlorate(VII),KCLO4,and potassium chloride. what is the maximum number of moles of ptassium chlorate(VII) which coulbe be produced from 0.2mol of potassium chlorate(V)?

原帖由 kensai 于 20/5/2006 23:07 发表
1) no of mol of compound = 12.4/128= 0.05 mol

1 mol of sodium thiosulphate give 2 mol of Na
so, 0.05 mol of sodium thiosulphate give 0.1 mol of NA

concentration of NA solution = 0.1 moldm^-3 ...

i tell u question again la
when potassium chorate(V) is heated strongly,it decomposes into potassium chlorate(VII),KCLO4,and potassium chloride. what is the maximum number of moles of ptassium chlorate(VII) which coulbe be produced from 0.2mol of potassium chlorate(V)?

kensai

3）2H2S(g)+SO2(g)-->2H2O+3S(s)

2。8 dm of H2S reacts with 1.4 dm of SO2

so, H2S remaining = 1.6 dm - 1.4dm =0.2 dm

不用 24 dm

4) Ca(OH)2 + CO2 -> CaCO3 + H2O

0.5 g of CaCO3 formed, Mr of CaCO3= 100.1
no of mol of CaCO3 formed = 0.5/ 100.1 =0.005

Since 1 mol of CO2 forms 1 mol of CaCO3
So,0.005 mol of CO2 forms 0.005 mol of CaCO3

1 mol occupies 24 dm cube,
so 0.005 mol CO2 occupies 24x 0.005= 0.12 dm cube

% of CO2 in air = 0.12 /100 x 100 =0.12%

5)CxHy  + oxygen ---〉 XCO2 + y/2 H2O
20 cm CxHy gives 60 cm CO2
1 mol CxHy gives 3 mol CO2
so, x = 3

20 cm CxHy gives 40 cm H2O
1 mol CxHy gives 2 mol H2O
so, y =2

so, formula of hydrocarbon = C3H2

kensai

原帖由 ~ciyun~ 于 20-5-2006 11:20 PM 发表

i tell u question again la
when potassium chorate(V) is heated strongly,it decomposes into potassium chlorate(VII),KCLO4,and potassium chloride. what is the maximum number of moles of ptassium c ...

4KCLO3 -> 3KCLO4 + KCL

0.2 mol of KCLO3 can produce 0.2 x 3/4 =0.15 mol of KCLO4

xabi1111

ate,ide represent wat????

xabi1111

how to draw sulphide eh dot and cross diagram

原帖由 kensai 于 20/5/2006 23:27 发表



4KCLO3 -> 3KCLO4 + KCL

0.2 mol of KCLO3 can produce 0.2 x 3/4 =0.15 mol of KCLO4

canu tell me how to find out 3/4?
1)a gaseous organic compound X was burnt in an excess of oxygen. A 0.112 dm cube sample of X, measured at s.t.p. produced 0.88g of carbon dioxide. how many carbon atoms are there in one molecule of X?

kensai

原帖由 ~ciyun~ 于 20-5-2006 11:43 PM 发表

canu tell me how to find out 3/4?
1)a gaseous organic compound X was burnt in an excess of oxygen. A 0.112 dm cube sample of X, measured at s.t.p. produced 0.88g of carbon dioxide. how many carb ...

3/4 是从这个 equation 找到的，
4KCLO3 -> 3KCLO4 + KCL

4 mol kcl03 gives 3 mol kcl04,
so 1 mol kclo3 gives 3/4 mol kclo4


X+ Oxygen -> Carbon dioxide

no of mol of CO2 = 0.88 / (12 +32) = 0.02 mol

at stp, volume carbon dioxide= 0.02 x 22.4 = 0.448 dm cube

0.112 dm cube X gives 0.448 dm cube carbon dioxide
so,1 mol X gives 4 mol carbon dioxide


1 molecule of x contains 4 carbon atoms

xabi1111

sulphate and sulphide 是不是S4 and S3

xabi1111

juz now ask is SO3 eh dot and cross diagram,sorry

原帖由 kensai 于 20/5/2006 23:55 发表



3/4 是从这个 equation 找到的，
4KCLO3 -> 3KCLO4 + KCL

4 mol kcl03 gives 3 mol kcl04,
so 1 mol kclo3 gives 3/4 mol kclo4


X+ Oxygen -> Carbon dioxide

no of mol of CO2 = 0.88  ...

oh is like that thx....
so if i have question to ask u just can use this way only?
got other way mah?
i got one question
a pure hydrocarbon was completely isolated from bottled gas used fot cooking and heating. when 10cm cube of the hydrocarbon were burned in 70cm cube of oxygen(an excess), the final gaseous mixture contained 30cm cube of carbon dioxide and 20cm cube of unreacted oxygen. allgaseous volumes were meansured under identical conditions. what is the fomula of the hydrocarbon?

[ 本帖最后由 ~ciyun~ 于 21-5-2006 12:26 AM 编辑 ]

kensai

原帖由 xabi1111 于 20-5-2006 11:40 PM 发表
how to draw sulphide eh dot and cross diagram

不是gua...这些找书就有了，

而且你要找的是 hydrogen sulphide, H2S?
还是 sulphide ion?  S-? 还是 什么？

ide 我不知道是什么


to ciyun

其实这些大多数都是form 4 ， form 5 的 basic, 可以说是 chemistry 里面最简单的 一个 chapter 了，

你在stpm以后学到的酱会比这个难很多，希望你想清楚自己可不可以应付 chemistry.

现在要换 subject 还早，如果迟点的话就不好了。

[ 本帖最后由 kensai 于 21-5-2006 12:07 AM 编辑 ]

原帖由 xabi1111 于 20/5/2006 23:59 发表
juz now ask is SO3 eh dot and cross diagram,sorry

actually u want ask wat?

xabi1111

i never study at form 4 and 5 but i'm now in upper 6 d ,so my foundation was very poor.only noe f6 eh things but donno f4 and 5 eh

xabi1111

i never study at form 4 and 5 but i'm now in upper 6 d ,so my foundation was very poor.only noe f6 eh things but donno f4 and 5 eh

xabi1111

SO3 eh lewis structure izzit have three dative bone ler???i'm not sure about tat???

kensai

Sulphate 是 so4,sulphite 是 so3
sulphide 是 s , 比如 hydrogen sulphide = h2s

xabi1111

so all salt eh bec which have O4 1 is ate and O3 1 is ite,rite.thanks for ur answer,i'll revised f4 and f5 and will not ask such easy question again

dunwan2tellu

原帖由 xabi1111 于 21-5-2006 12:10 AM 发表
SO3 eh lewis structure izzit have three dative bone ler???i'm not sure about tat???

是3个double bond 吧？  S = 0