The identity of a Group 1 metal carbonate may also be found by a titration method. M⁺ in this question may or may not be the same cation as that in Question 1. M₂CO₃(s) + 2HCl(aq) → 2MCl(aq) + H₂O(l) + CO₂(g) FA 3 is an aqueous solution containing 7.46gdm⁻³ of a Group 1 metal carbonate, M₂CO₃. FA 4 is 0.110 mol dm⁻³ hydrochloric acid, HCl. bromophenol blue indicator

1. (a)Method • Fill the burette with FA 4. • Pipette 25.0 cm³ of FA 3 into a conical flask. • Add a few drops of bromophenol blue indicator. • Carry out a rough titration and record your burette readings in the space below. The rough titre is .............................................. cm³. • Carry out as many accurate titrations as you think necessary to obtain consistent results. • Make sure any recorded results show the accuracy of your practical work. • Record, in a suitable form below, all your burette readings and the volume of FA 4 added in each accurate titration. I II III IV V VI VII [7][7]
2. (b)From your accurate titration results, calculate a suitable mean value to use in your calculations. Show clearly how you obtained this value. 25.0 cm³ of FA 3 required .............................................. cm³ of FA 4. [1][1]
3. (c)(i)Give your answers to (c)(ii), (c)(iii) and (c)(iv) to an appropriate number of significant figures. [1][1]
4. (c)(ii)Calculate the number of moles of hydrochloric acid present in the volume of FA 4 calculated in (b). moles of HCl = .............................................. mol [1][1]
5. (c)(iii)Calculate the number of moles of Group 1 metal carbonate, M₂CO₃, present in 25.0 cm³ of FA 3. moles of M₂CO₃ in 25.0 cm³ = .............................................. mol [1][1]
6. (c)(iv)Calculate the relative formula mass, Mr, of M2CO3. Mr of M₂CO₃ = .............................................. [1][1]
7. (c)(v)Identify the cation, M⁺. Show your working. M⁺ is .............................................. [1][1]
8. (d)A student carrying out a similar experiment, using the same method, found the cation in Question 2 to be Rb⁺. The student is told that the acid provided, FA 4, was incorrectly prepared. The cation in the student's experiment should have been identified as K⁺. State whether the acid supplied is more, or less, concentrated than 0.110 mol dm⁻³. Explain your answer. [1][1]