Practical 3 & 4: Gravimetric Analysis of Sulfate 65410 Skills for the Professional Chemist conecum re volupta evelignis Graphics created by Ullupta pe et doluptuam.
2 Pre-lab work • Chemical Safety – Safety Data Sheets provide crucial information regarding the use of chemicals. You will learn more about this in the lectures. • Precipitation reaction equation – The reaction occurring in today’s experiment involves aqueous barium and sulfate ions forming solid barium sulfate • Gravimetric analysis calculations – Using the mass of precipitated BaSO 4 to determine the mass of sulfate and sulfur in lawn fertiliser.
3 Gravimetric Analysis • Gravimetric analysis is the quantitative determination of an analyte by mass • We can use the precipitation method of gravimetric analysis to separate ions from a solution and find the amount of an aqueous ionic compound in a sample: 1. Precipitation reaction 2. Filter 3. Wash the precipitate 4. Dry precipitate 5. Weigh the precipitate
4 Gravimetric Analysis • When analysing something by mass, what is important? – Clean and dry glassware – Use of an analytical balance – Minimising sources of systematic error
5 General procedure today • Step 6 reads “slowly add the required amount of 0.5 M BaCl 2 ” BaCl 2 is the source of Ba 2+ ions that will be reacting with the SO 4 2- ions • in the fertiliser. Ba 2+ (aq) + SO 4 2- (aq) BaSO 4 (s) • You will need to calculate how much BaCl 2 reagent you need? – Assume that all of your initial fertiliser sample is sodium sulfate – Calculate moles of barium you need to precipitate out the sulfate – Convert moles into a volume of 0.5 M BaCl 2 – Add ~10% extra to ensure all of the sulfate turns to solid BaSO 4
6 Aims of this Practical • Calculate the required volume of 0.5 M BaCl 2 that needs to be added to the solution in order to precipitate ALL of the sulfate ions • Perform the experiment by following the general procedure provided in the guidelines • Calculate the mass of sulfate and sulfur present in the lawn fertiliser and compare with manufacturer’s quoted amounts • Re-design the experiment so that others can replicate your methods • Consider the risk assessment process and safety procedures that need to be followed before you undertake an experiment
7 Important considerations • How long will this experiment take? Can it be done in a 1 hour class or does it require a double period or more? • Do you need individual bottles of reagents in small volumes? • Think about your safety considerations – Should you be wearing gloves and why? – Is it hazardous? – Do we need to limit volumes? – Is it hot? • This practical runs over two weeks so you stop when you get to step 7
8 Laboratory Report 3 • Your report will consist of: – A re-written experimental method – Post-laboratory worksheet – Risk assessment (details given in workshop) – Scanned copy of labnotes • Keep in mind the purpose and audience for this report – a High School chemistry practical class • Further information is in the Practical 3 guide on UTSOnline
9 Laboratory Report 3 submission • Your individual report will be submitted as ONE FILE and must contain your scanned laboratory notes. – Convert report to pdf – Scan lab notes (as pdf) – Merge pdf files (using a website such as pdfmerge.com or Adobe Acrobat Pro DC) – Submit via the link in UTSOnline – You have 2 weeks to submit the report after the second of your two prac sessions.
Recommend
More recommend
