1. The procedure in an experiment are summarized below.
A mixture of castor oil and sodium hydroxide solution was heated gently with stirring for 15 minutes. After cooling down the mixture, a white solid X was obtained upon adding a colorless solution Y. X was then separated out and washed with distilled water.
A small amount of X was put in a test tube containing a mixture of water and a few drops of oil. The contents of the test tube were thoroughly shaken and the observation was recorded.
(a) If X is dissolved in water to form an aqueous solution, what would be observed in shaking a mixture of this solution and lime water? (1 mark)
2. Y is a compound containing carbon, hydrogen and oxygen only. When 0.15g of Y is completely burnt in oxygen. It gives 0.22g of carbon dioxide and 0.09g of water. If the relative molecular mass of Y is 60. show that the molecular formula of Y is C2H4O2.
The answer is C.
- 胡雪8°Lv 71 十年前最愛解答
A white solid (scum) is formed.
When castor oil is hydrolyzed in heated sodium hydroxide solution, soap (ROONa) is formed and separated. The soap solution forms scum with calcium ions in the lime water (Ca(OH)2 solution).
2RCOONa(aq) + Ca(OH)2(aq) → (RCOO)2Ca(s) + 2NaOH(aq)
Molar mass of CO2 = 12 + 16x2 = 44 g/mol
Molar mass of H2O = 1x2 + 16 = 18 g/mol
In 0.15 g of Y :
Mass of C = Mass of C in CO2 = 0.22 x (12/44) = 0.06 g
Mass of H = Mass of H in H2O = 0.09 x (1x2/18) = 0.01 g
Mass of O = 0.15 - (0.06 + 0.01) = 0.08 g
Mole ratio C : H : O = (0.06/12) : (0.01/1) : (0.08/16) = 0.005 : 0.01 : 0.005 = 1 : 2 : 1
Empirical formula = CH2O
Let molecular formula = (CH2O)n
(12 + 1x2 + 16)n = 60
n = 2
Hence, molecular formula = C2H4O2
3. Answer : C
Z is the strongest reducing agent (the most reactive metal), because Z can displace all other three metals from their solutions.資料來源： 胡雪八