I am having problems with my chemistry lab homework. Title: Determining the diss

ID: 709016 • Letter: I

Question

I am having problems with my chemistry lab homework. Title: Determining the dissociation of a weak acid using pH Measurements

Data:

Molarity of unknown acid1.0 M

NaOH solution: 0.500 M

Volume of Unknown acid, mL: 20.0 mL

Final Buret Reading, mL: 18.2 mL

Initial Buret Reading, mL: 6.25mL

Volume of NaOH solution, mL: 11.95 mL

Total Volume of solution, mL: .100 mL

pH reading: 4.32

I need to find the following: Calculating Ka of unknown acid

Initial number of moles for HAn(aq) & OH- (aq)

Number of moles at equilibrium: HAn(aq) & An-

Equilibrium concentration, mol L^-: HAn, An- & H3O^+

Ka ?

Slope of the line ?

Ka Determined slope

Please help

Plz show work so I can understand it

Initial no. of moles of acid = 0.02 x 1 = 0.02 moles = 20 millimoles

Number of moles of NaOH consumed = 11.95/2 = 5.98 millimoles

final no. f moles of An- = 20 - 5.98 = 14.02 millimoles so conc. of An- = 14.02 x 10^(-3)/0.1 = 14.02 x 10^(-2)

final no. of moles of HAn = 5.98 millimoles so conc. of HAn = 5.98 x 10^(-3)/0.1 = 5.98 x 10^(-2).

pH = pKa - log([An-]/[HA]) = 4.32

pKa = 4.32 + 0.37 = 4.69

So Ka = 10^(-4.69) = 2 x 10^(-5) (approx)

HAn is a weak acid.

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