急要! 3條 簡單的chem 問題~ 20點~攏明送分!!!!!!!!!!!!!

1) MW of NH4NO3 = 80. In NH4NO3, the weight of 2N (one from NH4 & the other one from NO3) is 14x2 = 28. So, the ratio of N is 28/80 = 35%. However, there is only 50% of this salt in the total mass. So, the amount of N contributed by this salt is only 35 x 50% = 17.5%.
MW of (NH4)2HPO4 = 132. In (NH4)2HPO4, the weight of 2N (from 2NH4) is 28. So, the ratio of N is 28/132 = 21.2%. Since there is only 40% of this salt in the total mass, the amount of N contributed by this salt will be only 21.2% x 40% = 8.48%. Similarly, ratio fo P = 31/132 = 23.48%. Since only 40% of this salt in the total mass andthe above one contains no P, so, the total P in the total mass will be = 23.48 x 40% = 9.39%. Therefore, the total N in the total mass is 17.5% + 8.48% = 25.98%.
2) The neutralization is 2NaOH + H2SO4 = 2H2O + Na2SO4
In 50cm3 of 2M NaOH, the amount of Na+ ions is 50/1000 x 2 = 0.1mol.
Since the sulfuric acid is in liquid form and it will not increase the volume of water. In addition, the 2mole of NaOH will give rise of 1 mole of Na2SO4. So, the mole of Na2SO4 will be = 0.1/2= 0.05mole.
The molarity of Na2SO4 will be 0.05mole / 50/1000 = 1M.
3) In group 3 metal, they will lose 3 electrons to obtain the octet structure and oxygen will gain two electrons to obtain the octet. To balance the equation, the reaction will be as follows:
2X + 3/2O2 = X2O3
In one oxide molecule, it will contain 3 oxygen atoms and 2 metal X atoms.
So, if 1.44g of oxygen is reacted and found in the molecule. the mole will be = 1.44/16 = 0.09. Since the ratio fo O and X in one molcule is 3:2. So, the mol of X willbe = 0.9/ (3:2) = 0.06mol. Since there is 1.62g of X is found in the molecule, the AW of X is 1.62/0.06 = 27. So, the answer will be B (27).
I hope you understand what I explained.

1)

NH4NO3 N 係裏面佔 (14+14)/(14+4+14+48)

NH4NO3 又佔全部的一半

即係 N 佔全部的一半的 28/80, 即係 1/2*28/80


(NH4)2HPO4 裏面又有 N

N 係裏面佔 14*2/(28+8+1+31+48)

NH4NO3 又佔全部的 0.4

即係 N 佔全部的 0.4 的 28/117, 即係 04*28/117 咁多mass



2)

2M sodium hydroxide"

2 mol sodium hydroxide in 1000cm cube water

即係有 2/20 mol sodium hydroxide in 50cm cube water

2/20 mol sodium hydroxide 有 2/20 mol Na ions

但係要用兩隻 Na 先至form 到一隻呢種鹽: (Na)2SO4 (SO4 無限量供給)

所以 2/20 mol Na 只可以form 到 1/20 mol (Na)2SO4 睇公式就知



3)

1.62g of a metal X (a group 3 element) combine with 1.44g of oxygen to form an oxide. What is the mass of X?


1 mol O 有 16g

1.44g O 有幾多 mol?

即係問 1.44g 裏面有幾多個16g

1.44g 裏面有 0.09 個16g, 即係 0.09 mol O (hold 住)


3 個 O 可以同 2 個 group 3 metal 結合. (因為 2 個 group 3 metal 先夠 6+ 去孭 3 個 O 6- )

0.09 mol O 可以同 0.06 mol group 3 metal 結合

0.06 mol 呢種 group 3 metal 重 1.62g

咁 一 mol 呢種 group 3 metal 重幾多 g ?

1 mol 0既重量 乘 0.06 mol = 1.62g

1 mol 0既重量 = 27g 係 Aluminium 呀!!!!