How many moles of H2X would be required to react with this quantity of NaOH?
Look at the equation the ratio of H2X to NaOH is 1:2. So if we have 0.0025 moles of NaOH then we will have 0.0025/2 moles of H2X = 0.00125. (iii) Calculate the relative molecular mass of H2X. The 0.00125 moles of H2X came from a total of 500 cm3 solution, so there must be 20 times as much in the orginal solution (500 /25). Therefore 0.00125 x 20 = 0.025 moles in 500 cm3. We know that the total mass of H2X was 2.25 grams at the beginning. Now use the mass formula to work out the relative molecular mass: RMM = mass / moles = 2.25 / 0.025 = 90 (iv) A hydrated form of the acid also exists, H2X.yH2O. A solution containing 6.30 g dm-3 of the hydrated acid has the same (molar) concentration as the solution of the anhydrous acid, H2X, originally used. Using this information and your answer from (b), calculate the value of y. (8 marks) Out of the 6.30 grams 2.25 grams must be due to H2X and therefore 6.30 – 2.25 grams must be due to the H2O in H2X.y H2O. This calculation is similar to empirical