Total Dissolved Solids Calculation (1 Viewer)

[laser6628]

So i was doing Q25a from the 2005 HSC and this TDS question comes up. Could someone explain how to do this? Thanks

http://www.boardofstudies.nsw.edu.au/hsc_exams/hsc2005exams/pdf_doc/chemistry_05.pdf

 

[jeffwu95]

a)So In this water, it will contain both suspended solids and dissolved solids, the procedure to determine the concentrations of TDS is to filter out the suspended solids with filter paper then to evaporate the remaining water to obtain just the dissolved solids (ie how boiling salty water will obtain salt)
0.19-0.16=0.03 grams of Suspended solids
45.59-45.33=0.26g of Dissolved Solids
thus the percentage of dissolved solids in the WHOLE sample of water is 0.26/500 times 100=0.052 percent (adjust for sig figs)

 

[jeffwu95]

b)The question specifies chemical test so dont say like AAS, i guess you could add Cl ions (HCl) to precipate the lead into lead chloride

 

[someth1ng]

a)So In this water, it will contain both suspended solids and dissolved solids, the procedure to determine the concentrations of TDS is to filter out the suspended solids with filter paper then to evaporate the remaining water to obtain just the dissolved solids (ie how boiling salty water will obtain salt)
0.19-0.16=0.03 grams of Suspended solids
45.59-45.33=0.26g of Dissolved Solids
thus the percentage of dissolved solids in the WHOLE sample of water is 0.26/500 times 100=0.052 percent (adjust for sig figs)

You might want to explicitly state that it is gravimetric analysis by filtration then evaporation of water to determine TDS, also, you should also say that "assuming 1mL of water=1 gram of water" because it is not pure/distilled water.

As for the chemical test, you should probably talk about addition of HNO3 then filtration then addition of NaCl or HCl and say that a white ppt would indicate the presence of Pb2+ ions.

 

[jeffwu95]

You might want to explicitly state that it is gravimetric analysis by filtration then evaporation of water to determine TDS, also, you should also say that "assuming 1mL of water=1 gram of water" because it is not pure/distilled water.

As for the chemical test, you should probably talk about addition of HNO3 then filtration then addition of NaCl or HCl and say that a white ppt would indicate the presence of Pb2+ ions.

Why exactly would you need to add HNO3? isnt addition of HNO3 just for the detection of carbonates

 

[someth1ng]

Why exactly would you need to add HNO3? isnt addition of HNO3 just for the detection of carbonates

On second thought, you probably don't need it in this one since lead is already in the solution and you just need to add acid but typically, you add HNO3 to remove the carbonates that could form a false precipitate.

CO3 2- + 2H+ --> H2O + CO2

Usually, it's just a precaution so you don't get a positive result that should be negative.