Chemistry Questions

2010-08-17 7:31 am

1.Compare two solutions of 1M CH3COOH(aq) and 1M HCl(aq) of the same volume. Which of the following properties will be the same for both solutions?
(1) Electrical conductivity
(2)The number of moles of NaOH needed for complete neutralization
(3) The temperature rise when they are completely neutralized by 1M NaOH(aq)
A (1) only B (2) only C (1) and (3) only D (2) and (3) only

2.Which of the following substances can dissolve in both dil HCl(aq) and excess dil NaOH(aq) and give the chemical equation.
A Cu(OH)2 B Fe(OH)2 C Fe(OH)3 D Zn(OH)2

3.Which of the following solutions could be used to separate the SO4 2- and CO3 2- from each other by precipitation?
A AgNO3(aq) B Ba(NO3)2(aq) C Fe(NO3)2(aq) D NaNO3(aq)

4.Which of the following methods is best for separating Cu from a mixture of Cu and CuO? Explain briefly.
A Add warm water, stir, filter and dry the residue
B Add hot dil H2SO4(aq), filter and dry the residue
C Add warm water, filter and heat the residue strongly
D Add hot dil NaOH(aq), filter and dry the residue

5.X is a white solid. When dil HNO3(aq) is added to X, a colourless gas is evolved. The resulting solution gives a white precipitate with dil HCl(aq). X could be
A (NH4)2SO4 B (NH4)2CO3 C PbCO3 D PbSO4

6.X is added to dil HNO3(aq) followed by Ba(NO3)2 (aq), a white precipitation forms. When X is added to dil NaOH(aq) until excess, a white precipitate which is soluble in excess alkali forms. X could be
A AlCl3 B Al2(SO4)3 C CaCl2 D CaSO4 (Give the chemical equation)

7.Which of the following methods is the most suitable for preparing PbSO4? GIve the chemical equation as well.
A Adding Pb to dil H2SO4(aq)
B Adding PbCO3 to dil H2SO4(aq)
C Adding Pb(NO3)2 to dil H2SO4(aq)
D Adding PbO to dil H2SO4(aq)

回答 (1)

用戶26240

2010-08-17 9:54 am

✔ 最佳答案

1. B (2) only

(1) incorrect
CH3COOH is a weak acid which is partly ionized in water to give H⁺ ions, while HCl is strong acid which is completely ionized in water to give H⁺ ions.
Therefore, 1 M HCl contains a higher concentration of H⁺ ions, and thus has a higher electrical conductivity.

(2) correct
Both CH3COOH and HCl are monobasic acid. If they have the same concentration and volume, they need the same number of moles of NaOH for complete neutralization.

(3) incorrect
CH3COOH is a weak acid, and neutralization involves the ionization of CH3COOH.
HCl is a strong acid, and neutralization between H⁺ and OH¯ ions does not involves the ionization of HCl.

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2. D Zn(OH)2

Among them, only Zn(OH)2 are amphoteric, which can dissolve in both dil HCl and dil NaOH.

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3. C Fe(NO3)2(aq)

Iron(II) ions give FeCO3 precipitate with CO3²¯ ions, but give no precipitate with SO4²¯ ions.

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4. B Add hot dil H2SO4(aq), filter and dry the residue

CuO reacts with dil H2SO4 to give CuSO4 solution, but Cu does not react. The Cu is filtered off as the residue. Dry the residue to obtain pure Cu.

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5. C PbCO3

PbCO3 reacts with dil HNO3 to give Pb(NO3)2 solution and colourless CO2 gas. The resulting solution contains Pb²⁺ ions which give a white precipitate with dil HCl to give white PbCl2 precipitate.

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6. B Al2(SO4)3

Al2(SO4)3 reacts with acidified Ba(NO3)2 to give white BaSO4 precipitate.
Al2(SO4)3(aq) + 3Ba(NO3)2(aq) → 3BaSO4(s) + 2Al(NO3)2(aq)

Al2(SO4)3 reacts with NaOH to form a white precipitate of Al(OH)3.
Al2(SO4)3(aq) + 6NaOH(aq) → 2Al(OH)3(s) + 3Na2SO4(aq)
Al(OH)3 reacts with excess NaOH to give soluble zincate.
Al(OH)3(s) + NaOH(aq) → Na[Al(OH)4](aq)

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7. C Adding Pb(NO3)2 to dil H2SO4(aq)

Pb(NO3)2 is soluble in water. In B, PbSO4 is formed by mixing two solutions.

If a solid reactant is involved, the PbSO4 coated on the solid reactants will separate the solid reactants and the dil H2SO4. This will stop the reaction soon after the reaction starts.

參考: bin_2630

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