With the given information, estimate H3O+ in a 2.0 M solution of each acid. Expr

Question

With the given information, estimate H3O+ in a 2.0 M solution of each acid. Express the molar concentrations to two significant figures. Help with Part C only please! Hrefo MasteringChemistry Assignment 6 (Chapter 15)- a htps/session masteringchemistry.com/myct/tem View assignmentProblemID-95 Assignment 6 (Chapter 15) Mozilla Problem 15.83 with feedback Constants I Periodic Table Acid FormulaK Formic HCO2H 1.8 x 101 Hydrocyanic | HCN | 4.0 × 10 10 Perchloric HCIO4 very large Hypobromous HOBr 2.0 x 109 You may want to reference (Pages 627 - 628) Section 15.10 while completing this problem.

Explanation / Answer

1)
HCO2H dissociates as:

HCO2H          ----->     H+   + HCO2-
2                 0         0
2-x               x         x


Ka = [H+][HCO2-]/[HCO2H]
Ka = x*x/(c-x)
Assuming x can be ignored as compared to c
So, above expression becomes

Ka = x*x/(c)
so, x = sqrt (Ka*c)
x = sqrt ((1.8*10^-4)*2) = 1.897*10^-2

since c is much greater than x, our assumption is correct
so, x = 1.897*10^-2 M



So, [H+] = x = 1.897*10^-2 M

2)

HCN dissociates as:

HCN          ----->     H+   + CN
2                 0         0
2-x               x         x


Ka = [H+][CN]/[HCN]
Ka = x*x/(c-x)
Assuming x can be ignored as compared to c
So, above expression becomes

Ka = x*x/(c)
so, x = sqrt (Ka*c)
x = sqrt ((4.9*10^-10)*2) = 3.13*10^-5

since c is much greater than x, our assumption is correct
so, x = 3.13*10^-5 M



So, [H+] = x = 3.13*10^-5 M

3)
Since it is strong acid, it will dissociate completely to give [H+] = 2.0 M

4)
HOBr dissociates as:

HOBr          ----->     H+   + OBr-
2                 0         0
2-x               x         x


Ka = [H+][OBr-]/[HOBr]
Ka = x*x/(c-x)
Assuming x can be ignored as compared to c
So, above expression becomes

Ka = x*x/(c)
so, x = sqrt (Ka*c)
x = sqrt ((2*10^-9)*2) = 6.325*10^-5

since c is much greater than x, our assumption is correct
so, x = 6.325*10^-5 M



So, [H+] = x = 6.325*10^-5 M

Answer:
1.9*10^-2 , 3.1*10^-5 , 2.0 , 6.3*10^-5

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