Approximately 7 mL of 6M Noah was diluted to 400 mL and standardized against 0.1

Question

Approximately 7 mL of 6M Noah was diluted to 400 mL and standardized against 0.1135M HCL . the initial volume reading was 0.16 mL for HCL and 0.04 mL for NaOH . upon reaching the pale pink phenolphthalein endpoint, the fine volume reading was 27. 36 for HCL and 35.26 for NaOHA 0.5736g sample of an unknown solid acid titrated with the above -standardized sodium hydroxide required 43.24 mL of base for neutralization. a. how many moles of OH- were required ? b. how many moles of H+ ions are in the unknown solid? c. determine the Em of the unknown solid?.

Explanation / Answer

Volume of NaOH used = 35.26 - 0.04

Volume of HCl used = 27.36 - 0.16

so using M1V1 = M2V2,

0.1135*(27.36-0.16) = x*(35.26 - 0.04)

or x=0.087 M

so the concentration of NaOH is 0.087 M.

a) moles of OH- used = 0.087*43.24*10^-3

=3.76*10^-3 moles

b)so moles of H+ in the solid = 3.76*10^-3 moles

c)enthalpy of the neutralization reaction

H+ + OH- => H2O is -57.7 kJ/mol

so Em of the solid = -57.7*3.76*10^-3 kJ

=-0.216 kJ

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