chem-3question

[匿名]

2011-02-13 12:44 am

Q1
The atomic no. of the element arsenic(As) is 33. Which of the following statements concerning the hydride of arsenic are correct?
1) Its chemical formula is AsH3.
2) It is very soluble in water.
3) Van der Waals' forces exist in the hyride.
A 1and2
B 1and3
C 2and3
D 1,2and3

ANS D

Q2 and 3 refer to the following experiment.

A drug tablet contains aluminium hydroxide as the only active ingredient. The following experiment was carried out to determine the amount of aluminium hydroxide in the drug tablet.

Step1 A drug tablet was dissolved in 50.0cm3 of 1.00 mol dm-3 HCL(aq) to form a solution.
Step2 The solution was diluted to 250.0cm3 with distilled water.
Step3 25.0cm3 portions of the diluted solution were titrated with 0.160 mol dm-3 NaOH(aq), using a suitable indicator. 25.8cm3 of NaOH(aq) were needed to reach the end point.

Q2
What is the no. of moles of HCL in 25.0 cm3 of the diluted solution?

ANS. 4.13X10-3 mol

Q3
What is the no. of moles of aluminium hydroxide in the drug tablet?

ANS. 2.90X10-3 mol

ths!

回答 (1)

己式庚辛

2011-02-14 9:20 am

✔ 最佳答案

1.
arsenic is a group V element, same as nitrogen. thus it should share some similar chemical properties with N.
i. valence electron is 3, so it can form tri-hydride, an analog to NH3 .
ii. NH3 is very soluble in water; quite safe to assume AsH3 is also soluble in water.
iii. similar to NH3, AsH3 also has simple molecular structure, so...

2.
it's "HCl".
HCl + NaOH ------> NaCl + H2O
no of mole of NaOH = molarity x volume = 0.160 x 25.8/1000 = 0.004128 mole

according to equation, mole ratio of NaOH : HCl = 1:1
so, no. of mole of HCl = ......

3.
total no. of mole of HCl in 250ml diluted product mixture
= 0.00413 x (250/25) = 0.0413 mole

originally, 50ml of 1M HCl is used
no. of mole of HCl = molariy x volume = 1 x 0.05 = 0.05 mole

thus, no. of mole of HCl reacted = 0.05 - 0.0413 = 0.0087 mole

then, write the chemical equation between HCl and Al(OH)3,
and determine the mole ratio of them.
thus, find the no. of mole of aluminium hydroxide.

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