Calculate the volume of 1M solution of HCl needed for 1 unit shift of the pH of

Question

                    Calculate the volume of 1M solution of HCl needed for 1 unit shift of the pH of thhe following solutions:
                

                    a. 100 mL of 0.1 M solution of weak acid (pKa = 6) and 0.05 M of its sodium                     salt.                 

                    b. 0.005 mole of sodium formiate and 23 g of formic acid dissolved in 100 mL of water.                     (pKa of formic acid = 3.75)                 

                    c. 100 mL of 0.1 M ammonia solution.                 

Explanation / Answer

Recall that M = (moles of solute/1 liter of solution)
So you got (12.0 moles of HCl / 1L)

The question is asking to figure out how many liters are needed to prepare 5L of .0250 M.

You can use M1V1 = M2V2 but I'm going to show you the long way so you can understand what's going on

5L x .0250 moles / 1L (Liters cancel out)
.125 moles of HCl

So set up an equation!

.125 mole of HCl = 12 moles x L
.125 / 12 moles moles = L
.0104 liters!

Using M1V1 = M2V2
12 M HCl x L = 0.0250 M2 X 5.00L
12 M HCl x L = .125ML
.125ML / 12M = .010416

In the future when you start going over titrations the M1V1 = M2V2 will not work because there will be different ratios. For now though you can do M1V1 = M2V2

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