f.4 chem
2007-03-13 5:21 am
2.the formula of a solid dibasic acid is H2X. 2.88g of the acid is dissolved in some distilled water and the solution is then diluted to 250cm^3 with distilled water. 25cm^3 of the dilute solution requires 16.0cm^3 of 0.4M sodium hydroxide solution for complete neutralization. what is the molar mass of H2X?
回答 (2)
2007-03-13 6:29 am
✔ 最佳答案
2NaOH + H2X -> Na2X + 2H2OSo, H2X mole = 1/2 * NaOH mole
= 1/2 * 0.4 *16/1000
= 0.0032 mol
So the number of mole of H2X in 250 cm^3 solution = 0.0032 * 10
= 0.032 mol
So the molar mass of H2X = 2.88 / 0.032
= 90
2007-03-13 6:23 am
The equation about the reaction between H2X and NaOH is
H2X(aq) + 2NaOH (aq) ---------> Na2X(aq) + 2H2O (l)
Therefore, 1 mole of H2X requires 2 moles of NaOH for complete neutralization
The number of mole of NaOH used in the reaction
= (16/1000)*0.4 mole
=0.016*0.4 mole
0.0064 mole
We can then know that there is a total of (0.0064/2) mole of H2X, which is 0.0032 mole
Let the formula of X be x
The molar mass of H2X is (1)(2) + x =2x
Therefore the number of mole of the 2.88 g of H2X is 2.88/(2+x) mole
The concentration of the solution formed in terms of molar
=( 2.88/(2+x) ) / (250/1000) M
=11.52/(2+x) M
The number of mole of H2X in 25cm^3 (25/1000 dm^3) solution
=11.52/(2+x) * 0.025 mole
=0.288/ (2+x) mole
Therefore, 0.288/(2+x) = 0.0032
_____________0.288=0.0064+0.0032x
___________0.0032x= 0.2816
_________________x=88
Therefore, the molar mass of H2X is (88+2) g mol^-1, which is 100g mol^-1
2007-03-14 18:33:14 補充：
Sorry guys, the molar mass SHOULD BE 90 gmol^-1, NOT 100g mol^-1
H2X(aq) + 2NaOH (aq) ---------> Na2X(aq) + 2H2O (l)
Therefore, 1 mole of H2X requires 2 moles of NaOH for complete neutralization
The number of mole of NaOH used in the reaction
= (16/1000)*0.4 mole
=0.016*0.4 mole
0.0064 mole
We can then know that there is a total of (0.0064/2) mole of H2X, which is 0.0032 mole
Let the formula of X be x
The molar mass of H2X is (1)(2) + x =2x
Therefore the number of mole of the 2.88 g of H2X is 2.88/(2+x) mole
The concentration of the solution formed in terms of molar
=( 2.88/(2+x) ) / (250/1000) M
=11.52/(2+x) M
The number of mole of H2X in 25cm^3 (25/1000 dm^3) solution
=11.52/(2+x) * 0.025 mole
=0.288/ (2+x) mole
Therefore, 0.288/(2+x) = 0.0032
_____________0.288=0.0064+0.0032x
___________0.0032x= 0.2816
_________________x=88
Therefore, the molar mass of H2X is (88+2) g mol^-1, which is 100g mol^-1
2007-03-14 18:33:14 補充：
Sorry guys, the molar mass SHOULD BE 90 gmol^-1, NOT 100g mol^-1
參考: My own chemistry knowledge
收錄日期: 2021-04-24 08:35:19
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