Chem HELP - Ans.fyi 參考答案

Chem HELP

Kya_19

2015-03-23 1:36 am

1) 25cm3 of 0.6M Na2SO4(aq) are mixed with 75cm3 of 0.2M Al2(NO4)3(aq). What molarity of cations in the resulting solution?

A. 0.3M
B. 0.6M
C. 1.2M
D. 2.4M

2) Graphene is pure carbon in the form of a thin sheet. The carbon atoms are arranged as inter-connected six-membered rings. In this structure, each carbon atom is shared by three rings. What is the average number of six-membered rings in 24.0g of graphene?
(Relative atomic mass: C=12.0; Avogadro constant = 6.02x10^23)

A. 2.01x10^23
B. 6.02x10^23
C. 1.20x10^24
D. 2.31x10^24

3) Same size and shap of iron nail immersed in following liquid
a) 1M AgNO3
b) 1M Zn(NO3)2
c) 1M H2O
Which of the following arrangement represents the ascending order of rate of corrosion of the iron nails?

A. Z<Y<X
B. Y<Z<X
C Z<X<Y
D X<Z<Y

回答 (1)

用戶26240

2015-03-23 6:44 am

✔ 最佳答案

1)
"Al2(NO4)3" should be "Al2(SO4)3"instead.

No. of moles of N a2SO4 = 0.6 × (25/1000) = 0.015 mol
No. of moles of N a⁺ = 0.015 × 2 = 0.03 mol

No. of moles of Al2(SO4)3 = 0.2 × (75/1000) =0.015 mol
No. of moles of Al³⁺ = 0.015 × 2 = 0.03 mol

Total number of moles of cations = 0.03 + 0.03 = 0.06 mol
Volume of the resulting solution = 25 + 75 = 100 cm³ =0.1 dm³

Molarity of cations in the resulting solution
= 0.06/0.1
= 0.6 M ...... The answer is B.

====
2)
No. of moles of C atom = 24/12 = 2 mol
No. of C atoms = 2 × (6.02 × 10²³)

No. of C atoms shared by a six-membered ring = 6 × (1/3) = 2
No. of six-membered rings
= 2 × (6.02 × 10²³) / 2
= 6.02 × 10²³ ...... The answer is B.

====
3)
a, b and c should be X, Y and Z respectively.

X is AgNO3. Iron undergoes displacement reaction with silver ions togive iron(II) ions. Iron(II) ions change to rust rapidly. Therefore, X speeds up rusting in the fastest rate among X, Y and Z.

Y contains mobile zinc and nitrate ions, which can also speed up rusting, butin a lower rate than X.

..... The answer is B.

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