Practical 3 & 4: Gravimetric Analysis of Sulfate 65410 Skills - - PowerPoint PPT Presentation

Practical 3 & 4: Gravimetric Analysis

• f Sulfate

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65410 Skills for the Professional Chemist

2

Pre-lab work

• Chemical Safety

– Safety Data Sheets provide crucial information regarding the use

• f 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 BaSO4 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 BaCl2”
• BaCl2 is the source of Ba2+ ions that will be reacting with the SO4

2- ions

in the fertiliser. Ba2+ (aq) + SO4

2- (aq)  BaSO4 (s)

• You will need to calculate how much BaCl2 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 BaCl2 – Add ~10% extra to ensure all of the sulfate turns to solid BaSO4

6

Aims of this Practical

• Calculate the required volume of 0.5 M BaCl2 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.