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18 Jul 2009, 12:21 AM
| #1 (permalink) |
| Member HSC: 2009 Gender: Female
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15 Nov 2009, 2:19 PM  | Calculation question*** You can hide this advertisement by registering. The Winkler method may be used to determine the concentration of DO in a sample of water. In the reaction, 1mole of oxygen produces 2 moles of iodine. The iodine is then titrated with Na2S2O3, using starch as an indicator, according to the equation:I2 + 2Na2S2O3 --> 2NaI + Na2S4O6 A 500 mL sample of river water was analysed using the Winkler method. 4.80 mL of 0.100mol/L Na2S2O3 solution was required to titrate the iodine that was formed. a) Calculate the number of moles of iodine that was formed. b) Calculate the concentration of oxygen in the river water in mol/L I did a) and got the answer 2.4x10^-4 moles, but have no idea about question b? anyone please help? thanks@!! |
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19 Jul 2009, 10:22 PM
| #3 (permalink) | |
| Member HSC: 2009 Gender: Female
Join Date: Apr 2008
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15 Nov 2009, 2:19 PM | Re: Calculation question*** Quote:
I dont know.. coz this question is from the hw given by my tutor.. | |
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19 Jul 2009, 10:38 PM
| #4 (permalink) |
| Supreme Member HSC: 2008 Gender: Undisclosed
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Today, 1:03 PM | Re: Calculation question*** Okay here it is: your answer to (a) is correct. for Na2S2O3: n=cv c=0.100mol/L and v=0.00480L therefore n=4.8 x 10^-4 moles ratio of I2 to Na2S2O3 is 1:2 therefore to get the number of moles of I2, divide number of moled of Na2S2O3 by 2 thus n(I2)=2.4x10^-4 moles (b) we know 1 mole of O2 produces 2 moles of I2 thus n(O2) = 0.5 X n(I2) = 0.5 x 2.4x10^-4 moles = 1.2x10^-4 moles but we need concentration of O2 c=n/v here n = 1.2x10^-4 moles as calculated v=0.5 litres (given) thus c(O2)= 2.4 x 10^-4 mol/L hope that helps Last edited by Pwnage101; 19 Jul 2009 at 11:55 PM. |
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20 Jul 2009, 9:17 PM
| #6 (permalink) | |
| <3 Prophet 9 AyyyTAR Hater  HSC: 2009 Gender: Female Location: Sydney
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Today, 1:51 PM  | Re: Calculation question*** Quote:
__________________ Courses: Extension 1 + 2 maths, Chemistry, Physics, Modern History and Advanced English UAI aim: 99+  Click the user bars to join the groups of the era   Want a friendly tutor with experience and plenty of resources? Click here, but hurry as there's only one slot left! | |
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1 Nov 2009, 5:47 PM
| #8 (permalink) |
| Member  HSC: 2010 Gender: Male
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7 Nov 2009, 9:26 AM | Re: Calculation question*** Wimkler method isnt in HSC, so it wont be in any past papers.
__________________ Is god willing to prevent evil, but not able? Then he is not omnipotent. Is he able, but not willing? Then he is malevolent. Is he neither willing nor able? Then why call him god???? - Epicurus |
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