chem 15MARKS!!!急問呀!!

1)
One mole of calcium chloride (CaCl2) contains 1 mole of Ca2 cations and 2 moles of Cl- anions. There are totally 3 moles of ions, but not atoms.

2)
The unit of molar mass is g mol-1.
When molar mass is given in CE question, because 「molar mass」 means 「mass per mole」, the molar mass is thus given in g.

3)
Potassium permanganate decomposed in light to give MnO2 and O2­. Therefore, it is stored in brown bottle.
Other common substances stored in brown bottles include concentrated nitric acid (HNO3) and silver nitrate (AgNO3).

4)
You have copy option A incorrectly. Option A is:
A. Ag + 2H NO3- → Ag NO2 + H2O
Option A is correct, while others are incorrect.

5)
(1):
HsSO4 + NaCl → NaHSO4 + HCl
(2):
HsSO4 + NaBr → NaHSO4 + HBr
H2SO4 + 2HBr → SO2 + 2H2O + Br2
(3):
HsSO4 + NaI → NaHSO4 + HI
H2SO4 + 8HI → H2S + 4H2O + 4I2
It is most probably out of the presence HKCE syllabus. Check it.

6)
A is incorrect.
HCl is a strong acid, which is completely ionized in water to give H (aq) and Cl-(aq). Theus, HCl exists as ions in the solution.

7)
Sulphur dioxide reacts with magnesium with a bright white flame.
2Mg SO2 → 2MgO S

8)
The melting points increase and then decrease.
Across Period 2 or Period 3, the first few elements are metals. The melting points increase as the increase in the numbers of delocalized electrons in each metal atom.
The maximum melting point occurs at Group 4 (carbon, silion). This is because the atoms are held together by networks of strong covalent bonds, and the covalent bonds are almost completely broken in melting.
The last few elements are molecular. Therefore, their melting points are very low.
What you say 「不是molar mass 愈大,b.p和m.p都是愈大的嗎??」 is correct for molecular compounds only.

1. should be 3 mole of IONs but not atoms
because in ionic compounds, they exist as ions but not atom.

2. gmol-1

3. since potassium permangate solution would undergo decomposition under sun light.....yes, there are other substances needed to be stored in brown bottle...like conc. nitrics acid as you have mentioned

4. since conc. HNO3 would oxidize Ag....so Ag ions are formed(so B is wrong)
for C and D, i don't know as actually, A,C and D are not balanced?!?

5. halide salt can be oxidized by conc H2SO4/H3PO4 to form halogen, however, Cl cannot undergo such reaction because Cl2 is a stronger oxidizing agent than conc. H2SO4/H3PO4.

6. since HCl would completely ionized in water, so HCl exist as ions in the solution

7. i don't know

8. molar mass larger, bp/mp higher....this only holds for simple molecules.....since, mteal/ionic/giant covalent high mp and bp.....somple molecules low bp and mp.....as across a period, ionic>giant covalent>simple molecules....so decrease