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CIE Jun 2016 v4 Paper 3 Q1
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![Borax is an alkali which has many uses. In this experiment you will determine x in the chemical formula of borax, Na2BxO7.10H2O, by titration with hydrochloric acid. PMT II III IV VI VII FB 1 is a solution containing 15.5 g dm3 of borax, Na2BxO7.10H2O. FB 2 is 2.00 mol dm3 hydrochloric acid, HCl. methyl orange indicator (a) Method Dilution of FB 2Pipette 10.0 cm3 of FB 2 into the 250 cm3 volumetric flask. Make the solution up to 250 cm3 using distilled water. Shake the solution in the volumetric flask thoroughly. This diluted solution of hydrochloric acid is FB 3. Label the volumetric flask FB 3. TitrationFill the burette with FB 3. Pipette 25.0 cm3 of FB 1 into a conical flask. Add several drops of methyl orange. Perform a rough titration and record your burette readings in the space below.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 FB 3 added in each accurate titration. The rough titre iscm3. (b) From your accurate titration results, obtain a suitable value for the volume of FB 3 to be used in your calculations. Show clearly how you obtained this value. [7] 25.0 cm3 of FB 1 requiredcm3 of FB 3. [1]UCLES 2016 9701/34/M/J/16<br />
PMT (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 hydrochloric acid present in the volume of FB 3 calculated in (b). (ii) 1 mole of borax is neutralised by 2 moles of hydrochloric acid. Calculate the number of moles of borax that react with the hydrochloric acid in (i). moles of HCl =mol (iii) Use your answer to (ii) to calculate the number of moles of borax in 1.00 dm3 of FB 1. moles of borax =mol moles of borax in 1.00 dm3 FB 1 =mol (iv) Use your answer to (iii) and the information on page 2 to calculate the relative formula mass, Mr, of borax. (v) Calculate x in the formula of borax, Na2BxO7.10H2O. Use data from the Periodic Table on page 12. Mr of borax =UCLES 2016 9701/34/M/J/16 x =[5] [Total: 13] [Turn over<br />](https://learnah.org/wp-content/uploads/2018/08/June_2016_v4_QP_-_Paper_3_CIE_Chemistry_A-level_1-0.jpg)
![Page 2 Question (a) Cambridge International AS/A LevelMay/June 2016 9701 34 Mark Scheme Syllabus Paper Indicative material Mark Total [7] I Initial and final readings and titre value given for rough titre and 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 / FB3 and used / addedunit: / cm3 or (cm3) or in cm3 or cm3 (for each heading) III All accurate burette readings are 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 for0.30 (cm3) Award V and VI for 0.30 cm3 <0.60 (cm3) Award V for 0.60 cm3 <1.00 (cm3)Cambridge International Examinations 2016<br />
Page 3 Question (b) Cambridge International AS/A LevelMay/June 2016 9701 34 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(HCl) used = 0.008b( ) 1000 (ii) (iii) Correct use of factors n(borax) = 0.5answer (i) and n(borax) = 40answer (ii) (iv) Correct use of (iii) and 15.5 Mr = 15.5 iii( (v) Correct expression x = (iv)338 ( ) 10.8 All answers to 3 or 4 significant figures and if answer (v) is attempted it must be an integer Question 2Cambridge International Examinations 2016<br />](https://learnah.org/wp-content/uploads/2018/08/June_2016_v4_MS_-_Paper_3_CIE_Chemistry_A-level_1-0.jpg)
