Question

EDTA revised procedure (No need to make your own standard solution as stated in the original instructions) Equipment needed 2 x 125 ml E. Flasks, 3x 250ml E. Flasks, 1x500ml E. Flask, 3 watchglasses, 1x10ml Volumetric Pipet, 1 pipet bulb, 1x10 ml graduated cylinder, 1xBuret, 1 wash bottle and 1 slop beaker 600ml NOTE Do not dump any solutions down the drain- use slop beaker and then empty beaker into waste bottles by the sinks. Goggles and Lab Coat needed. work station# 1 to 15 - do step #1 then #2// Work Station 16-30 do step# 2 first then # 1 1-Set up 25ml Buret and get equipment needed from drawer 2-Go to Stockroom with 500 ml Flask to get 250 ml of 0.01M EDTA. Cover with watchglass 3- Pour 80 mls of Standard Solution (from 500ml Plastic Bottle at your bench) into a 125 ml E. Flask flask# 1) Cover with calculations watch glass. Record concentration value from the bottle. You will need it for your a 4- Pour 30 mls of Buffer PH10 solution (from 500ml Plastic Bottle at your bench) into a 125ml E. Flask (flask#2). Cover with a watch glass. 5 After rinsing Buret with a small amount of EDTA solution . Fill Buret with the EDTA solution. 6-After rinsing the 10 ml volumetric pipet with some standard solution (flask #1), add 10 mls of standard solution to an E-flask. 7-Add 2 drops of Eriochrome black T indicator and 5 ml of the pH Buffer 10 (use graduated cylinder) to the titration flask 8- Titrate with EDTA solution. Record volume used. Repeat 3 times. Empty flasks into slop beaker and rinse. 9- Rinse 125 ml E. Flask (flask #1) and go to stockroom to get 100mls of unknown. Cover with watch glass 10- After rinsing 10 ml volumetric pipet with some of the unknown solution pipet 20 mls of unknown into 250 ml E. Flask. Add indicator and pH 10 Buffer (#8). Titrate with EDTA. Repeat 3 times
Please find the molarity of CaCo3 standard given that the concentration is 179mg/100mL. Then please answer the questions and calculations below.

Answer 1

1) The molarity of CaCO₃ standard can be obtained with a unit factor:

ImolCacos 1,000mL mol (0.179gCaCOs)100.09gCaco 0.0179M 0.0179- 100m L 1L

2) The average volume of EDTA used to titrate the standard solutions is:

17.5m L+ 17.3mL+17.4mL = 17.4mL Va,std

3) The average volume of EDTA used to titrate the unknown solutions is:

14.1mL14.2mL+14.5mL Va,unk 14.3mL 3

4) To know the concentration of the unknown solution first we need to know the concentration of EDTA, this is done using the standard titration (Remember that each mol of EDTA combines with 2 mol of Ca²⁺):

0.0179molCac0s ImolEDTA 1, 000mL 1 ) 2molcaco17.4mL CEDTA (10m Lstnd) 1, 000mLstnd 1L 5.14 103M 5.14m M 5.14 10-37mol

Now we can know the concentration of the unknown solution:

5.14* 103molEDTA 2molCaco 1 1, 000mL (14.3mLEDTA) Cunkown 1molEDTA 20mL 1, 000mLEDTA 1L -3 mol 7.35 10 M 7.35m M 7.35 10 _