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[thebrianlee]

31. Evaluate the following industrial processes using the principles of green chemistry. (a) Two-stage fermentation process for vitamin C production (b) Haber process for ammonia production (c) CATIVA process for acetic acid production

[thebrianlee]

30. Methanol can provide energy by direct combustion. It can also be used as a fuel in fuel cells. (a) Write a chemical equation for the combustion of methanol. (b) In a fuel cell, aqueous methanol is oxidized to give carbon dioxide and hydrogen ions. Write a half equation for the reaction involved. (c) Hydrogen can also be used as a fuel in fuel cells. Suggest ONE advantage and ONE disadvantage of using methanol over hydrogen as fuel in fuel cells. (d) Suggest the hazard warning labels that should be put on a cylinder of methanol. (e) Besides using as a fuel, suggest ONE other use of methanol.

[thebrianlee]

33. It is suggested that the chloroalkali industry can provide the raw material, hydrogen, for the Haber process and the manufacture of methanol.

(d) The steam-methane reforming is commonly used to make syngas for the production of methanol. (i) What is syngas? (ii) Suggest ONE advantage of using syngas as the raw materials to produce methanol over obtaining hydrogen from the chloroalkali industry. (e) Suggest ONE advantage and ONE disadvantage of setting up the Haber process and chloroalkali industrial plants together at the same site. (Hint: You can consider the social, economic or environmental aspect.)

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[thebrianlee]

If a melting ice cube of 20 g is added to a milk tea of 25°C, the final temperature of the iced milk tea is 20°C. If two ice cubes, each of 20 g, are added to the same milk tea at the same initial temperature, which of the following statements about the final temperature of this iced milk tea is correct? Assume that the heat lost to the surroundings can be neglected. Given: specific latent heat of fusion of ice = 3.34 x 10^5 J kg

specific heat capacity of water = 4200 J/kg°C

A. Lower than 15°C

B. Equal to 15°C

C.Higher than 15°C

D. Cannot be determined since the mass of the milk tea is unknown

[thebrianlee]

[HKAL 2006 II Q4a]

The overall reaction for the discharging process of a lead-acid cell can be represented by the following equation:

PbO2(s) + Pb(s) + 4H+(aq) + 2SO4 → 2-(aq) 2PbSO4(s) + 2H2O(l)

(i) Write the half equation of the cathodic reaction and that of the anodic reaction during discharge for a lead-acid cell.

(ii) Using the IUPAC conventions, write the cell diagram of a lead-acid cell.

(iii) Based on the above information, explain why a lead-acid cell is rechargeable.

(iv) A lead-acid accumulator used in automobiles consists of six lead-acid cells connected in series.

Suggest why

(I) the state of charge of a lead-acid accumulator can be estimated by measuring the density of the acid in the accumulator, and

(II) an excessively high voltage should not be used to charge a lead-acid accumulator.

[thebrianlee]

2020 Ⅰ

14. The coordinates of the points A and B are (-10,0) and (30,0) respectively. The circle C passes through A and B. Denote the centre of C by G. It is given that the y-coordinate of G is -15 .

(a) Find the equation of C.

(b) The straight line L passes through B and G. Another straight line l is parallel to L. Let P be a moving point in the rectangular coordinate plane such that the perpendicular distance from P to L is equal to the perpendicular distance from P to l. Denote the locus of P by Γ. It is given that Γ passes through A.

(i) Describe the geometric relationship between Γ and L.

(ii) Find the equation of Γ.

(iii) Suppose that Γ cuts C at another point H. Someone claims that ∠GAH <70°. Do you agree? Explain your answer.

[thebrianlee]

van 't Hoff equation

\ln K = - \frac{{\Delta H^\ominus}}{RT}

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DSE 2020 Ⅱ

41. Find the range of values of c such that the circle x²+y²-6x +cy -7=0 and the straight line x-y+9=0 intersect.

A. -56≤c≤8

B. -8≤c≤56

C. c≤-56 or c≥8

D. c≤-8 or c≥56

[thebrianlee]

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[thebrianlee]

Q8

Solid X gives a gas with dilute hydrochloric acid. When dilute aqueous ammonia is added to a solution of X, a white precipitate forms. The precipitate dissolves in excess alkali. X could be A aluminium carbonate. B aluminium sulphate. C zinc carbonate. D zinc sulphate.

[thebrianlee]

Q7

An aqueous solution of compound X reacts with barium nitrate solution to give a white precipitate. This aqueous solution of X gives a white precipitate With dilute sodium hydroxide solution. X could be A calcium chloride. B iron(ll) chloride. C magnesium sulphate. D potassium sulphate.

[thebrianlee]

Q5

Which of the following solutions would NOT a precipitate with sodium carbonate solution? A Aluminium sulphate solution B Ammonium nitrate solution C Lead(ll) nitrate solution D Magnesium sulphate solution

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Q4

Dilute aqueous ammonia is added successively to four different solutions. Which of the following combinations is correct?

  Solution                                           Observation

Calcium chloride                            yellow precipitate  Chromium(lll) sulphate                   white precipitate Iron(lll) sulphate                             green precipitate Potassium chloride                          no precipitate