IMPORTANT INFORMATION: Due to the on-going COVID-19 pandemic, this practical class will be online. This means that you will be given the experimental data in order for you to complete the electronic SMARTSHEET for assessment. Please follow the guide below:    1. Read this laboratory script carefully and make sure you understand the underlying chemistry.  2. In the modules folder, read the Pre-lab work pages and access the titration related pages (e.g. how to carry out a titration and how to use a pipette). These pages give you access to the relevant videos that will aid your understanding.  3. Once you are happy, use the data provided at the end of this document (in red) and use it to complete the assessment (SMARTSHEET).   Introduction In a titration experiment a strong acid is slowly added from a burette to known volume of base until amount of acid added neutralizes the amount of base present. This is known as the end point and is accompanied by the change in colour of an indicator solution added to the base at the beginning of the titration. If the concentration of the base is accurately know (called a standard solution) then the unknown concentration of the acidic solution can be calculated and that acidic solution is then said to be standardized. Solutions of strong acids (eg HCl) may be standardised using a standard solution of borax (sodium tetraborate decahydrate, Na2B4O7.10H2O). Likewise, solutions of strong bases (eg NaOH) may be standardized using a solution of KHP (potassium hydrogen phthalate). Borax and KHP are commonly used as standards as both solids have a high molecular weight, making them easy to weigh accurately, and are air-stable (they don’t absorb moisture from the air, effecting their molecular composition). The first part of this practical involves the standardization of HCl (accurately determining the concentration of the acid) using the standard solution of borax. The second part of this practical uses the standardized hydrochloric acid solution to titrate against a solution of an unknown carbonate withe a molecular formula of X2CO3 where X is the unknown element.   Learning Objectives To become proficient in the use of a burette as demonstrated by obtaining concordant results. To prepare a solution from a solid using the weighing by difference method. To apply calculations of moles, molar mass, concentrations and dilutions. To apply the concept of valency to assess the validity of the results obtained.   Underlying Chemistry A standard solution of borax with a concentration of 0.04 mol dm-3 will be provided. The reaction of borax with hydrochloric acid proceeds according to the chemical reaction:  Na2B4O7.10H2O + 2 HCl → 4 H3BO3 + 2 NaCl + 5 H2O   From the chemical equation it can be seen that 2 moles of HCl are required to reaction with each mole of borax. Thus, the ratio of number of moles of acid to borax is:   which can be written as:                                                              or     The reaction of carbonate with hydrochloric acid proceeds as follows: X2CO3(aq) + 2HCl(aq) → 2XCl(aq) + H2O(l) + CO2(g) where X is an unknown element. Thus, the ratio of number of moles of acid to carbonate is:      Safety Notes Chemicals: ChemicalHazard Information Sodium tetraborate decahydrate Na2B4O7.10H2O 0.04 mol dm-3  Hazardous in case of inhalation. Slightly hazardous in case of skin contact (irritant), of eye contact (irritant), of ingestion. No long term health hazards when in solution. Should not be released into the drain. Hydrochloric acid HCl ~ 0.1 mol dm-3 Not classified as hazardous or dangerous at this concentration. Unknown carbonate X2CO3      Causes serious eye irritation. Methyl Orange C14H14N3NaO3S Not classified as hazardous or dangerous at this concentration.   PPE: As this practical involves working with an irritant it is advised that you should wear gloves for the practical session.  Handle all glassware with care. If a breakage occurs please inform your demonstrator and allow them to dispose of the broken pieces.   Waste Disposal: All solutions containing borax (both the standard solution provided and the solutions resulting from the titrations in part A) need to be disposed of in the waste containers provided. They should not be disposed of down the sink. All other solutions can be disposed of down the sink.     Methodology     PART A:   Standardisation of the Hydrochloric Acid Solution   1. Collect ~ 150 cm3 of the standard borax solution in a clean dry beaker.   2. Pipette 25.00 cm3 aliquots of the borax solution into each of three 250 cm3 conical flasks.   3. Add to each flask 5-6 drops of methyl red indicator. The solution will be yellow.   4. Obtain a sample (ca. 100 cm3) of hydrochloric acid in a clean dry beaker.   5. Use a funnel to fill the burette with the HCl solution. Remember to lower the burette to below shoulder height before filling it. Also remember to close the tap of the burette before adding any solution. You do not need to fill your burette to the zero mark. You should fill your burette to a level which is comfortable to read a eye level when returned to a position above the bench.   6. Remove the funnel, return the burette to it’s normal position above the bench, run a little of the solution through the tap to remove any air bubbles below the tap. Record the initial reading on the burette.   7. Assign one student within the pair to titrate the borax solution using the hydrochloric acid, added from the burette, to the orange end point. Overshooting the end point will give a red solution. The colour change should be effected by the addition of one drop of titrant. Record the final reading on the burette. The difference in these two volumes recorded is your titration volume.   8. Repeat the titration of the other aliquots of borax solutions until you achieve concordant titrations, that is two titre values which agree to 0.1 cm3 or better.   9. Dispose of your solutions in the waste containers provided and rinse out your conical flasks.   The concentration of the hydrochloric acid solution can now be calculated by calculating the number of moles of borax in the aliquot and using the volume of HCl used.   PART B:   Identification of an Unknown Carbonate   1. Using a 4 decimal place balance weigh accurately approximately 2.0 g of the unknown carbonate into to a clean dry weighing boat (a mass anywhere between 1.9 – 2.1 g is acceptable). To do this: i) tare the balance, ii) add the weighing boat and note the mass shown, iii) add approximately 2.0 g of the unknown carbonate to the boat. iv) Record the mass of the carbonate and the boat, that is, do not tare the balance after you place the boat on.   2. Carefully transfer the contents of the weighing boat to a 250 cm3 volumetric flask via a DRY glass funnel. Re-weigh the weighing boat and any adhering carbonate. Record this mass also (boat and the residue).   The difference in the two masses measured in steps 1 and 2 is the mass of carbonate which has been transferred to the volumetric flask. This procedure is called “weighing by difference”.   3. Tap the funnel on the volumetric flask so that most of the carbonate falls through into the flask. Wash the remainder of the solid from the funnel into the volumetric flask using a jet of water from a wash bottle, rinsing the funnel well before removal.   4. Dissolve the solid by adding distilled water to the volumetric flask until the bulb is ~ 3/4 full (shaking will be required). Finally dilute to the mark with distilled water, carefully adding the last few cm3 with a plastic dropping pipette. Mix thoroughly by inversion of the flask.   5. Pipette 25.00 cm3 aliquots of this solution into each of three 250 cm3 conical flasks, and add 5-6 drops of methyl red indicator to each flask.   6. Use a funnel to re-fill the burette with the HCl solution (remember to do this safely by lowering the burette to below shoulder height). Remove the funnel and record the initial reading on the burette.   7. Ensuring that the second student within the pair now performed the titrations: Titrate with your standardised hydrochloric acid solution to the end point, which is indicated by a colour change from yellow to red, ideally stopping at orange. Repeat the titration with the other aliquots to give at least two (preferably three) results that agree within 0.1 cm3.     The identity of the carbonate can be determined from the molar mass of the powder. This can be calculated from the number of moles of acid used to neutralise the carbonate and the molar mass of the carbonate weighed out.     Before leaving the laboratory Ensure that your demonstrator has marked you as present on the register Dispose of any solutions in the correct manner (those containing borax in the waste container provided, all others are permitted to go down the sink). Rinse all of your used glassware with tap water Place all rinsed glassware in the grey drawers of the trolley (except for burettes). Place used burettes in the elephants foot in the window. Please separate the glassware so that beakers are in one drawer, pipettes in another drawer, conical flasks in another drawer etc. If a drawer is full, put your glassware in the drawer below. Do not build a mountain of glassware!   Results to be used for the SMARTSHEET assessment Section A: Borax standard solution Borax standard solution preparation: 16.01 g was dissolved in 1 Litre (1000 cm3). Section B: Standardisation of HCl solution Table 1: Titration data for standardisation of HCl solution Titration number  Volume of HCl used to reach end-point (cm3)Titration 120.95 Titration 221.05Titration 321.00   Section C: Determination of the identity of the carbonate Amount of unknown carbonate used = 2.02 g Table 2: Titration data for standardisation of HCl solution Titration number Volume of HCl used to reach the end-point (cm3)138.05238.00337.95