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CIE Jun 2016 v5 Paper 3 Q1
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![In this experiment you will determine the concentration of a solution of sulfuric acid by titration. PMT FA 1 is sulfuric acid, H2SO4. FA 2 is aqueous sodium hydroxide, containing 4.20 g NaOH dissolved in 1.00 dm3 of water. thymolphthalein indicator (a) Method Dilution of FA 1Pipette 10.0 cm3 of FA 1 into the 250 cm3 volumetric flask. Make the solution up to the mark using distilled water. Shake the flask thoroughly. This diluted solution of sulfuric acid is FA 3. Label the flask FA 3. TitrationFill the burette with FA 2. Pipette 25.0 cm3 of FA 3 into a conical flask. Add a few drops of thymolphthalein indicator. Perform a rough titration and record your burette readings in the space below. The end point is reached when the solution turns a permanent pale blue colour. The rough titre iscm3. Carry out as many accurate titrations as you think necessary to obtain consistent results. Make sure any recorded results show the precision of your practical work. Record in a suitable form below all of your burette readings and the volume of FA 2 added in each accurate titration. Keep solution FA 1 for use in Questions 2 and 3. II III IV VI VII [7]UCLES 2016 9701/35/M/J/16<br />
PMT (b) From your accurate titration results, obtain a suitable value for the volume of FA 2 to be used in your calculations. Show clearly how you obtained this value. 25.0 cm3 of FA 3 requiredcm3 of FA 2. [1] (c) Calculations Show your working and appropriate significant figures in the final answer to each step of your calculations. (i) Calculate the number of moles of sodium hydroxide present in the volume of FA 2 calculated in (b). Use the data in the Periodic Table on page 16. moles of NaOH =mol (ii) Complete the equation for the reaction of sulfuric acid with sodium hydroxide. State symbols are required.+Na2SO4(aq) +(iii) Use your answers to (i) and (ii) to calculate the number of moles of sulfuric acid used in each titration. (iv) Calculate the concentration, in mol dm3, of sulfuric acid in FA 3. moles of H2SO4 =mol (v) Calculate the concentration, in mol dm3, of sulfuric acid in FA 1. concentration of H2SO4 in FA 3 =mol dm3 concentration of H2SO4 in FA 1 =mol dm3 [5]UCLES 2016 9701/35/M/J/16 [Total: 13] [Turn over<br />](https://learnah.org/wp-content/uploads/2018/08/June_2016_v5_QP_-_Paper_3_CIE_Chemistry_A-level_1-0.jpg)
![Page 2 Question (a) Cambridge International AS/A LevelMay/June 2016 9701 35 Mark Scheme Syllabus Paper Indicative material Mark Total Initial and final readings and titre value given for rough titre and I initial and final readings for two (or more) accurate titrations (minimum of 2 x 2 box) II Titre values recorded for accurate titrations and Appropriate headings for the accurate titration table and cm3 units.initial / start burette reading / volume / value final / end burette and reading / volume / value titre or volume / FA2 and used / added unit: / cm3 or (cm3) or in cm3 or cm3 (for each heading) III All accurate burette readings recorded to the nearest 0.05 cm3. Do not award this mark if:50(.00) is used as an initial burette readingmore than one final burette reading is 50(.00)any burette reading is greater than 50(.00) IV There are two (or more) uncorrected, accurate titres within 0.10 cm3Do not award this mark if, having performed two titres within 0.1 cm3, a further titration is performed which is more than 0.10 cm3 from the closer of the two initial titres, unless a further titration, within 0.10 cm3 of any other, has also been carried out.Do not award the mark if any accurate burette readings (apart from initial 0 cm3) are given to zero dp. V, VI and VII Examiner rounds any accurate burette to the nearest 0.05 cm3, checks subtractions and then select the best titres using the hierarchy:two (or more) accurate identical titres, then two (or more) accurate titres within 0.05 cm3, then two (or more) accurate titres within 0.10 cm3, etc. These best titres should be used to calculate the mean titre, expressed to nearest 0.01 cm3. Accuracy marks are awarded as shown. Award V, VI and VII Award V and VI Award V only if0.20 cm3 if 0.20 <0.40 cm3 if 0.40 <0.60 cm3 [7]Cambridge International Examinations 2016<br />
Page 3 Question (b) Cambridge International AS/A LevelMay/June 2016 9701 35 Mark Scheme Syllabus Paper Indicative material Mark Total [1] [5] [13] Candidate must take the average of two (or more) titres that are within a total spread of not more than 0.20 cm3. Working must be shown or ticks must be put next to the two (or more) accurate readings selected. The mean should be quoted to 2 dp, rounded to the nearest 0.01. Two special cases where the mean may not be to 2 dp:Allow mean expressed to 3 dp only for 0.025 or 0.075 (e.g. 26.325)Allow mean if expressed to 1 dp if all accurate burette readings were given to 1 dp and the mean is exactly correct. (e.g. 26.0 and 26.2 = 26.1 is allowed) (e.g. 26.0 and 26.1 = 26.1 is incorrectshould be 26.05.) Note: the candidates mean will sometimes be marked as correct even if it is different from the mean calculated by the examiner for the purpose of assessing accuracy. (c) (i) Correctly calculates n(NaOH) used = 4.20 ( ) b 40.0 1000 (ii) (iii) Equation correct 2NaOH(aq) + H2SO4(aq)Na2SO4(aq) + 2H2O(l) State and symbols must be correct and answer (i) divided by 2 (iv) Correct use of 40answer (iii) (v) Correct use of 25answer (iv) All answers to 3 or 4 significant figures (minimum 3 answers attempted) Question 1Cambridge International Examinations 2016<br />](https://learnah.org/wp-content/uploads/2018/08/June_2016_v5_MS_-_Paper_3_CIE_Chemistry_A-level_1-0.jpg)
