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If the concenuaion of hydroxide in a solution of calcium hydroxide is x. what is

ID: 923158 • Letter: I

Question

If the concenuaion of hydroxide in a solution of calcium hydroxide is x. what is the concentration of calcium ion in ihc same sample If a 20,00-mL solution of only calcium hydroxide (not saturated) requires 11.25 mL of 5.25 x 10^-3 M HCI to titrate to the methyl orange endpoint, what was the concentration of hydroxide ion in the solution A 50.00 ml. aliquot of a saturated volution of gold (III) hydroxide. Au(OH)_3. is titrated by 0.058 M HCI. If it takes 47.22 mL. of the titrant to reach the methyl orange endpoint. how many moles of hydroxide ion were neutralized What is the concenration of hydroxide ion in the saturated Au(OH), solution described in question #5

Explanation / Answer

Solution :-

Q3) Ca(OH)2 is the calcium hydroxide

1 mol Ca(OH)2 gives 2 mol OH-

So if the concentration of the OH- = x

Then concentration of the Ca(OH)2 = x/2

Q4)

To find the concentration of the hydroxide ion we can use the molarity and volume of the HCl solution

Molarity of the hydroxide = molarity of HCl * volume of HCl / volume of Ca(OH)2 solution

                                             = 5.25*10^-3 M * 11.25 ml / 20.00 ml

                                            = 2.95*10^-3 M

So the concentration of the hydroxide ion = 2.95*10^-3 M

Q5) lets calculate the moles of the HCl using the molarity and volume

Moles of HCl= molarity * volume in liter

                      = 0.058 mol per L * 0.04722 L

                     = 0.002739 mol HCl

Mole ratio of the HCl and OH- is 1 : 1

Therefore moles of the hydroxide ion neutralized = 0.002739 mol OH-

Q6)

Moles of OH- in the previous part = 0.002739 mol

So the moles of the Au(OH)3 are calculated as

0.002739 mol OH- * 1 mol Au(OH)3 / 3 mol OH- = 0.000913 mol Au(OH)3

Now lets calculate the molarity of the Au(OH)3

[Au(OH)3] = moles / volume in liter

                  = 0.000913 mol / 0.050 L

                 = 0.01826 M Au(OH)3

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