Stock Solutions: (These will be prepared for you, but you should come to lab wit

Question

Stock Solutions: (These will be prepared for you, but you should come to lab with the calsulations written ont in your lab book for making 100 mL. each of Stock Solution A and B. Include all units) A) 0.20 MNaH:PO H:O (monobasic sedium phosphate) (FW of monobasic, monohydrate is 137.99) B) 020MNa:HPOs (dibasic sodium phosphate) (FW of anhydrous dibasie is 41.96) 1. You will be provided 100 ml each of Solution A and Solution B 2. Prepare the 12 solutions noted in the table below by combining the specified amounts of Solutions A, B, and water. Measure the pl of the prepared solutions before, and after, challenge with either HC1 or NaOH, as specified in the table. Calculate the change in plH after challenge and enter the value in the table

Explanation / Answer

Molarity: it is a measure of the concentration of solute in a solution. It is defined as the number of moles of solute present in 1 liter of solution.

Molarity = no of moles/volume of solution

            M = n/V (in liters)

If n = weight (wt) /Molecular weight (M.Wt)

Then

M = wt/ M.Wt *1/ V (in liters)

Or

M = wt/ M.Wt *1000 / V (in milliliters)

Stock A) preparation of 0.20 M NaH2PO4.H2O (monobasic sodium phosphate) (FW of monobasic monohydrate is 137.99)

100ml of 0.20 M stock solution A preparation:

Weight of solute                     = (x)? gm

Molecular weight of glucose   =137.99g/mol

Volume of solution                 =100ml

Molarity (M) = wt/ M.Wt *1000 / V (in milliliters)

0.20M= x gm/ 137.99*1000 / 100 (in milliliters)

x gm=0.032*137.99*100/1000

=2.759gm

Take 2.759 gm of NaH2PO4.H2O and dissolve in the 100ml of double distilled water then you will get 100ml of 0.20M NaH2PO4.H2O solution.

Stock B) preparation of 0.20 M Na2HPO4 (dibasic sodium phosphate) (FW of anhydrous dibasic is 141.96)

100ml of 0.20 M stock solution B preparation:

Weight of solute                     = (x)? gm

Molecular weight of glucose   =141.96g/mol

Volume of solution                 =100ml

Molarity (M) = wt/ M.Wt *1000 / V (in milliliters)

0.20M= x gm/ 141.96*1000 / 100 (in milliliters)

x gm=0.032*141.96*100/1000

=2.839gm

Take 2.839 gm of Na2HPO4 and dissolved in the 100ml of double distilled water then you will get 100ml of 0.20M Na2HPO4 solution.

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