GASES stoichiometry2

shuk yi

2009-02-23 1:07 am

at elevated temperatures, NaClO3 decompose to produce NaClO and oxygen gas. A 0.8765g sample of impure sodium chlorate was heated until the production of oxygen gas xeased. the O2 collected over water occupied 57.2ml at 295K and pressure of 734 torr, calculate the mass percent of NaClO3 in the original sample ( at 295K the capor pressure of water is 19.8 torr)

ANS is 18.0%

THANK YOU

回答 (1)

老爺子

2009-02-24 4:41 am

✔ 最佳答案

The question is mistyped. The sentence "NaClO3 decompose to produce NaClO and oxygen gas" should be "NaClO3 decompose to produce NaCl and oxygen gas".

Consider the O2 gas formed:
V = 57.2 mL = 0.0572 L
P = 734 - 19.8 = 714.2 torr
R = 62.36 L torr K-1 mol-1
T = 295 K

PV = nRT
(714.2)(0.0572) = n(62.36)(295)
No. of moles of O2, n = 0.002221 mol

2NaClO3 → 2NaCl + 3O2
No. of moles of O2 formed = 0.002221 mol
No. of moles of NaClO3 = 0.002221 x (2/3) = 0.001481 mol
Molar mass of NaClO3 = 22.99 + 35.45 + 16x3 = 106.44 g mol-1
Mass of NaClO3 used = 0.001481 x 106.44 = 0.1576 g
Mass % of NaClO3 in the sample = (0.1576/0.8765) x 100% = 17.98% ≈ 18%
=

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