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 November 25th, 2018, 08:07 AM #1 Member   Joined: Nov 2012 From: The Netherlands Posts: 40 Thanks: 2 Help with a Titration Issue Hi All I am the father of my 16 year Old Son. We are in the Netherlands , so please do not mind the language translation in the problem description. also, I can not render the text here, co Calcium carbonate is caco3 and 10 to the power minus four is : 10 -4 But I hope that would be forgiven . He has come to me with a titration issue which I can not resolve myself. He has done his Bit, but we both think that the approach has not been good . This is the Problem description and the solution that my son has tried to achieve: ++++++++++++Snip+++++++++++++++++++++ In a beaker 100 ml HCL, a 1 gram paper with Caco3 was dipped inside . from the 100 ml solution , (a reaction will take place) and now we took 10 ml out into a new a beaker ''B'' then The amount of gram of paper that we used: 1.00 grams The molarity of hydrochloric acid (HCl) used: 0.09 The molarity of sodium hydroxide solution (NaOH) used: 0.12 1) we used 8.30 ml (8.3 x 10 -3 L) of Naoh in a buret to dip inside beaker B Question is: what is mass % of Caco3 from the 1 gram paper. OUR SOLUTION(My Son's): what we have done : Calculation for the number of moles of H₃O⁺ in the 100ml solution before paper which came in(got dipped in): Mol H₃O⁺ 0.09 mol/lts X = 0.09 mole x 0.1 L1.00 L = 9 x 10 -3 mole HCL Thus 9 x 10 -3 mol H₃O⁺ ions are contained in a solution of 100 ml hydrochloric acid Calculation for the number of moles OH- in the 100 ml solution before paper came in: Mol OH-0.12 X used= Liter OH- 1.00 8.30 x 10 -3 X = 0.12 mole x 8.3 x 10 -3 L1.00 L = 9.96 x 10 -4 moles Thus 9.96 x 10 -4 mol OH - ions are contained in a solution of 8.30 ml hydrochloric acid. We used 8.3 NaOh ml from the buret . So there are also 9.96 x 10 -4 mol of H₃O⁺ ions in a solution of 8.30 ml of hydrochloric acid, because the ratio between the reaction of the H₃O⁺ ions and the OH ions is 1: 1. See below: OH- (ag) + H₃O⁺ (aq) → 2H2O (l) In order to know how many moles of H₃O⁺ ions have reacted with the OH - ions, you have to subtract the number of moles of H₃O⁺ ions contained in the 100 ml hydrochloric acid solution with the number of moles of H₃O⁺ ions to which you have titrated (Beaker B) . Thus 9 x 10 -3 moles - 9.96 x 10 -4 mole = 8.004 x 10 -3 moles. So 8,004 x 10 -3mol H₃O⁺ ions have reacted. To determine the amount of mole of CaCO₃ you must divide the number of reacted moles of H₃O⁺ ions by 2, because the reaction H₃O⁺ reacts with CaCO₃ in the ratio 2: 1. See the comment below: CaCO₃ (s) + 2H₃O⁺ (aq) → Ca²⁺ (aq) + CO₂ (g) + 3H₂O (l) Thus 8.004 x 10 -3 mol ÷ 2 = 4.002 x 10 -3mol. So there are 4.002 x 10 -3 moles of CaCO₃ parts in a 10 ml solution. If we round this in the correct number of significant digits you will get 4.002 x 10 -3mol CaCO3 parts in a 10 ml solution. Calculation for the number of grams of CaCO₃ in 4.002 x 10 -3 mol CaCO₃: Mol CaCO3 1.00 4.002 x 10 -3 Gram CaCO3 100.09 X X = 4.002 x 10 -3 mol x 100.09 gram1.00 mol = 0.40 gram ( in Beaker B) So there is 0.40 grams of CaCO₃ in 4.00 x 10 -3 moles of CaCO3. now what we have done is: 0.4 gms in 10 ml (Beaker B), gives 4 gm in the initial 100 ml HCL solution ,but this cant be true beacause the paper was 1 gram , and we can not have 4 grams of caco3 on the paper (as the solution to this problem will always be < 1 gram). where have we gone wrong here ? +++++++++++++++End Snip ++++++++++++++++++++++++++++++++++ Thanks for any assistance ! Regards November 26th, 2018, 11:07 AM #2 Member   Joined: Nov 2012 From: The Netherlands Posts: 40 Thanks: 2 Hi All Thanks to all. ITMT, we have resolved this issue. Just for the records , we consulted : and came to know why were we approaching this in a wrong manner. Thanks all. Tags issue, titration Thread Tools Show Printable Version Email this Page Display Modes Linear Mode Switch to Hybrid Mode Switch to Threaded Mode Similar Threads Thread Thread Starter Forum Replies Last Post markosheehan Chemistry 0 September 10th, 2017 05:50 AM rnck Physics 0 September 4th, 2013 12:36 AM bigcity Algebra 3 January 2nd, 2012 11:09 AM adhiluhur Chemistry 0 November 19th, 2010 09:00 PM Darpa.Chief Physics 1 April 15th, 2010 02:09 AM

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