Required Practicals

Question 1

• RP1: Make up a volumetric solution and carry out a simple acid-base titration
• STEPS FOR MAKING A SOLUTION

Answer 1

• Weigh the sample bottle containing the required mass of solid on a 2dp balance
• Transfer to beaker
• Reweigh empty sample bottle
• Record the difference in mass
• Add 100cm3 of distilled water to the beaker. Use a glass rod to stir to help dissolve the solid
• Sometimes the substance may not dissolve well in cold water so the beaker and its contents could be heated gently until all the solid had dissolved
• Pour solution into a 250cm3 graduated flask via a funnel
• Rinse beaker and funnel and add washings from the beaker and glass rod to the volumetric flask
• Make up to the mark with distilled water using a dropping pipette for last few drops. Ensure meniscus rests on calibration line
• Invert flask several times to ensure uniform solution

Question 2

RP1: Make up a volumetric solution and carry out a simple acid-base titration
• Describe how to prepare 250cm3 of an aqueous standard solution of ethanedioic acid containing an accurately measured mass of the acid

Answer 2

• Accurately weigh out a dry sample of ethanedioic acid using a high precision (minimum 2dp) balance
• Transfer to a beaker and reweigh weighing boat to determine mass transferred
• Dissolve acid in a small volume of distilled water, stirring with a glass rod
• Transfer to a VOLUMETRIC flask and rinse all equipment transferring rinsings too
• Add deionised water up to calibration line using dropping pipette at end
• Ensure meniscus rests on calibration line
• Stopper bottle and invert 10 times to homogenise solution

Question 3

RP7: In the iodine clock reaction, I reacts with hydrogen peroxide to form I2. This reacts with HSO: and forms further iodide ions, until the supply of HSO, is exhausted. At this stage, 12 forms a blue complex with starch.
You are given solution A, containing iodide ions, solution B containing hydrogen peroxide, and a starch solution. Describe how you would design a series of experiments to determine the order of reaction with respect to the iodide ions.

Answer 3

• Perform a series of experiments in which only the concentration of solution A varies.
• All volumes remain the same.
• [B] + [starch] stay the same
• Temperature controlled using a water bath
• Add 5cm3 of solution B and 1cm3 of starch to the beaker
• Simultaneously add 5cm3 of solution A and start timer
• Record time taken for blue colour to appear
• Dilute solution A so concentration is half the original
• Repeat experiment and record time taken
• Use 1/time taken for blue to appear as surrogate rate
• If rate x2 when [A] x 2, reaction is first order with respect to A
• If rate does not change when [A] x 2, reaction is 0 order with respect to A
• if rate x4 when [A] x 2, reaction is second order with respect to A

Question 4

Answer 4

• In each experiment, use a known volume and concentration of B, C and X
• Place B, C and X in a conical flask
• Add a known volume and concentration of A to the flask and start the timer
• Stop the timer when the blue colour is seen
• Rate is proportional to 1/t
• Repeat the experiment using same volume and concentrations of B, C and X
• Keep temperature the same using a water bath
• Change the concentration of A (keeping the total volume the same)
• Do this for 4/5 concentrations of A
• Plot a graph of 1/t against [A]

Question 5

RP1: Why should you not heat or put hot solutions in the graduated/volumetric flask?

Answer 5

• Do not heat or put hot solutions in the volumetric flask because the heat would cause the flask to expand and the volume would then be incorrect