送分呀~ 中4chem~20分

1.
(a)
The crucible is not completely covered in order to allow the water vapour and the expanded air to leave the crucible.
The crucible is not completely opened in order to avoid the solid spilling out.

(b)
Molar mass of Na2CO3 = 23*2 + 12 + 16*3 = 106 g mol-1
Molar mass of H2O = 1*2 + 16 = 18 g mol-1

Mole ratio Na2CO3 : H2O
= (23.62-21.5)/106 : (23.98-23.62)/18
= 0.02 : 0.02
= 1 : 1

Hence, x = 1

(c)
Some water vapour condenses into water drops and sticks on the lid. Therefore, the experimental mass of Na2CO3 becomes greater, the experimental mass of water becomes smaller.



2.
(a)
Mole ratio C : Cl : F
= 14/12 : 41.5/35.3 : 44.4/19
= 1.17 : 1.17 : 2.34
= 1 : 1 : 2

Empirical formula = CClF2

Mass of 1 dm3 of CFC-114 = 3.71 g
Mass of 46.1 dm3 of VFV-114 = 3.71 * 46.1 = 171 g
Molar mass = 171 g mol-1

Let (CClF­2)n be the molecular formula.
n(12 + 35.5 + 19*2) = 171
n = 2

Molecular formula = C2Cl2F4

(b)
This is because the C-Cl and C-F bonds are strong and not easy to break.

(c)
CClF2-CClF2 and CCl2F-CF3
=