# 化學題目尋求答案

Compound X2Y is 60% X by mass. Calculate the percent Y by mass of the compound X2Y2.

A)20%

B)30%

C)40%

D)60%

E)80%

Which pair of ions would not be expected to from a precipitate when dilute solutions of each are mixed?

A)cu2+ s2-

B)ag+ cl-

C)ca2+ po4 3-

D)mn2+ oh-

E)mg2+ so4 2-

### 4 個解答

• 御風
Lv 4
1 0 年前
最佳解答

我先說聲抱歉,我從以前到現在沒用過英文回答化學問題耶...這應該是大學才用的吧?所以我就用中文回答唷^^*

Compound X2Y is 60% X by mass. Calculate the percent Y by mass of the compound X2Y2.

A)20%

B)30%

C)40%

D)60%

E)80%

這題其實就是道爾吞的"倍比定律"的運用,

倍比定律內容：若兩元素可以生成兩種或兩種以上的化合物時，在這些化合物中，一元素的質量固定，則另一元素的質量成簡單整數比。

所以這題可以簡單的用一個九宮格來呈現

X Y

-------- --------- ------------

X2Y 60 40 當我們把X固定時,可知Y的比例為1:2

-------- --------- ------------ 所以所求Y的所佔的比例為80/60+80=57.1

X2Y2 60 80 故答案應選擇 D

Which pair of ions would not be expected to from a precipitate when dilute solutions of each are mixed?

A)cu2+ s2-

B)ag+ cl-

C)ca2+ po4 3-

D)mn2+ oh-

E)mg2+ so4 2-

這題需要用到離子沉澱表,所以還是需要背一下喔!!

(A)會產生CuS沉澱 (黑色)

(B)會產生AgCl沉澱 (白色)

(C)會產生Ca3(PO4)2沉澱 (白色)

(D)會產生MnO2沉澱 (綠色)

http://mail.mcjh.kl.edu.tw/~jcchen/ware/asp.htm

以上的網站可以點進去參考看看喔((離子沉澱表....

2010-04-30 22:29:38 補充：

對不起..

九宮格打起來有點亂

X Y

----- ------- --------

X2Y 60 40

----- ------- --------

X2Y2 60 80

當我們把X固定時,可知Y的比例為1:2

所以所求Y的所佔的比例為80/60+80=57.1

故答案應選 D

2010-04-30 22:36:10 補充：

痾ˇ...

好像還是依樣吼!!

那我用數學的數列來說好了..

(1,1)是空白

(1,2)是X

(1,3)是Y

(2,1)是X2Y

(2,2)是60

(2,3)是40

(3,1)是X2Y2

(3,2)是60

(3,3)是80

參考資料： Me, Me, me
• 小白
Lv 7
1 0 年前

wanszeto是對的

• 1 0 年前

Compound X2Y is 60% X by mass. Calculate the percent Y by mass of the compound X2Y2.

There is no exact answer from A to D

The closet answer is D) 60%

Let a g/mol and b g/mol be the molar masses of X and Y respectively.

In X2Y, mass ratio X : Y

2a : 1b = 60 : (100 - 60)

2a : b = 60 : 40

a : b = 30 : 40 = 3 : 4

In X2Y2, mass ratio

= 2x3 : 2x4

= 3 : 4

Percent Y by mass of the compound X2Y2

= [4/(3+4)] x 100%

= 57.1%

Which pair of ions would not be expected to from a precipitate when dilute solutions of each are mixed?

E) Mg2 + SO4 2-

MgSO4 is soluble in water.

CuS, AgCl, Ca3(PO4)2 and Mn(OH)2 are insoluble in water.

參考資料： wanszeto
• ?
Lv 4
1 0 年前

Compound X2Y is 60% X by mass. Calculate the percent Y by mass of the compound X2Y2.

for X2Y

X = 0.3

Y= 0.4

====================

FOR X2Y2

X2Y2= 0.6+0.8 = 1.4

Y = 0.4/1.4 =0.286---------------(B)

Which pair of ions would not be expected to from a precipitate when dilute solutions of each are mixed?

(D)

2010-05-01 17:51:20 補充：

FOR X2Y2

X2Y2= 0.6+0.8 = 1.4

Y = 0.4/1.4 =0.286---------------(B)====> 寫錯了Y = 0.8/1.4 =0.57