1. A,B,X and Y represent four different compounds. A and B react according to the following equation: A+2B->2X+Y
a grams of A react with b gram of B to give x grams of X and y grams of Y. What is the value of y?
2. 2Al + 3CL2->2AlCl3 In a certain experiment, 8.1 g of Al were heated with excess Cl. 38.2g of AlCl3 were obtained. What is the percentage yield of AlCl3?
3. A solid mixture consists of 1.0 mole of CaCO3 and 1.0 mole of Na2CO3. What is the number of moles of HCl(aq) required to liberate all the CO2 from the mixture?
4. When 100 g of pure CaCO3 reacted with excess HCl(aq), 44g of CO2 were obtained. However, in a similar experiment using 100g of impure CaCO3, 46g of CO2 were obtained. Assuming that the impurity is a metallic carbonate, what would this impurity be?
5. Which of the following reagents can be used to distinguish between HNO3(aq) and HCl(aq) and give the chemical equation.
A BaCl2(aq) B dil. NaOH(aq) C AgNO3(aq) D ZnCO3
6. Equal mass of marble chips(excess) were added to 100cm3 of 1M HCl(aq) and 100 cm3 of 1M CH3COOH(aq) separately. Which of the following would have been the same for both acids?
A The time taken for the reaction to complete
B The rate at which the first 10cm3 of gas was evolved
C The mass of marble chips left over when the reaction had stopped
D The average rate of the reaction
7. When a certain aqueous solution is diluted, its electrical conductivity decreases but its pH remains constant. What is the solution?
A HCl(aq) B NaCl(aq) C KOH(aq) D H2SO(aq)
Chem Qs
2010-08-15 7:31 am
回答 (1)
2010-08-15 10:43 am
✔ 最佳答案
1. A + 2B → 2X + Y
According to the law of mass conservation:
Mass of reactants = Mass of products
a + b = x + y
Hence, y = a + b - x
2.
2Al + 3Cl2 → 2AlCl3
No. of moles of Al used = 8.1/27 = 0.3 mol
Maximum no. of moles of AlCl3 formed = 0.3 mol
Maximum mass of AlCl3 formed = 0.3 * (27 + 35.5*3) = 40.05 g
% yield of AlCl3 = (38.2/40.05) * 100% = 95.38%
3.
CaCO3 + 2HCl → CaCl2 + H2O + CO2
No. of moles of CaCO3 used = 1 mol
No. of moles of HCl reacted with CaCO3 = 1 * 2 = 2 mol
Na2CO3 + 2HCl → 2NaCl + H2O + CO2
No. of moles of Na2CO3 used = 1 mol
No. of moles of HCl reacted with Na2CO3 = 1 * 2 = 2 mol
No. of moles of HCl required = 2 + 2 = 4 mol
4.
More CO2 is formed. Hence, the no. of moles of the impure carbonate used is more than that of pure CaCO3.
No. of moles = Mass/(Molar mass). Hence, the molar mass of the metallic carbonate impurity is smaller than that of CaCO3.
Hence, in the impurity MxCO3, x times the atomic mass of M is smaller than the atomic mass of Ca.
The impurity may be MgCO3, BeCO3 or Li2CO3 etc.
5.
The answer is: C AgNO3
Chemical equation: AgNO3(aq) + HCl(aq) → AgCl(s) + HNO3(aq)
6.
The answer is: C The mass of marble chips left over when the reaction had stopped
C is correct.
The excess marble chips are left over when the acid is completely reacted.
A, B and D are incorrect.
HCl is a strong acid while CH3COOH is a weak acid, and thus 1 M HCl(aq) contains a higher concentration of hydrogen ions than 1 M CH3COOH. Therefore, when 1 M HCl(aq) is used, the rate is faster and the time taken is shorter.
7.
The answer is: B NaCl(aq)
B is correct.
NaCl is neutral with pH 7. When diluted, the decrease in the concentration of ions leading to the decrease in electrical conductivity, but pH remains 7.
A, C and D are incorrect.
HCl and H2SO4 are acidic. When diluted, the decrease in the concentration of hydrogen ions leading to the increase in pH.
KOH is alkaline. When diluted, the decrease in the concentration of hydroxide ions leading to the decrease in pH.
參考: bin_2630
收錄日期: 2021-04-13 17:26:32
原文連結 [永久失效]:
https://hk.answers.yahoo.com/question/index?qid=20100814000051KK01816