唔該請chem.高手幫我解解題,thank you....

2009-07-24 6:05 pm

唔該請chem.高手幫我解解題...請唔好只係話個答案俾我聽,我想知個答案點得返來.因為我真的不知怎樣做...THANK YOU VERY MUCH....

1.Which of the following acids,when heated with copper,would produce a gas?
A. dilute nitric acid B. dilute hydrochloric acid C.dilute sulphuric acid D. concentrated ethanoic acid

2Which of the following pairs of solution, when mixed, would give a neutral solution?
A.10cm3 of 1M sulphuric acid and 10cm3 of 1M sodium hydroxide solution.
B.10cm3 of 1M sulphuric acid and 10cm3 of 2M sodium hydroxide solution.
C.10cm3 of 2M sulphuric acid and 20cm3 of 1M sodium hydroxide solution.
D.20cm3 of 2M sulphuric acid and 10cm3 of 2M sodium hydroxide solution.

3.Consider the following chemical equation:
xVO2+ (aq) + yH+ (aq) +2I- (aq) -----> xVO2+ (aq) +zH2O(l) + I2(aq)

(Vis the symbol for the element vanadium.)
Which of the following combinations is correct?

x y z

A. 1 2 1
B. 1 4 2
C. 2 4 2
D. 3 6 3

4. In which of the following reactions does nitrogen exhibit three different oxidation numbers in the species involed?

A. NH4NO3-------->N2O + 2H2O
B. 8NH3 + 3CL2--------> 6NH4Cl + N2
C. Mg + 4HNO3------->Mg(NO3)2 + 2NO2 + 2H2O
D. 3Cu + 8HNO3------> 3Cu(NO3)2 + 2NO +4H2O

回答 (1)

六呎將軍

2009-07-24 7:06 pm

✔ 最佳答案

(1) Hydrochloric acid and ethanoic acid are not strong oxidizing agent, so they won't react with copper at all regardless of the concentration.
For sulphuric acid, it is a strong oxidizing agent only when concentrated. Therefore dilute sulphuric acid also does not react with copper.
So ans is A.
In fact dilute nitric acid acts as an oxidizing agent rather than an acid when reacting with metals, giving nitrogen monoxide gas.
(2) A. No. of moles of H+ ions = 0.02 and no. of moles of OH- ions = 0.01. Therefore it is NOT a complete neutralization
B. No. of moles of H+ ions = 0.02 and no. of moles of OH- ions = 0.02. Therefore it is a complete neutralization
C. No. of moles of H+ ions = 0.04 and no. of moles of OH- ions = 0.02. Therefore it is NOT a complete neutralization
D. No. of moles of H+ ions = 0.04 and no. of moles of OH- ions = 0.01. Therefore it is NOT a complete neutralization
Ans: B
(3) Oxidation no. of V changes from +5 to +4, and that of I changes from -1 to 0.
So they have the same amount of change in oxidation no. and hence x = 2 since the coefficient of I- is 2 in the equation.
Then 2 O atoms have to be pulled out to form water, giving y = 4 and z = 2
Ans = C
(4) A. N in NH4+ = -3, N in NO3- = +5 and N in N2O = +1. So 3 different oxidation nos. are shown.
B. N in NH3 = -3, N in NH4+ = -3 and N in N2 = 0. So 2 different oxidation nos. are shown.
C. N in NO3- = +5 and N in NO2 = +4. So 2 different oxidation nos. are shown.
D. N in NO3- = +5 and N in NO = +2. So 2 different oxidation nos. are shown.
Ans: A

參考: Myself

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