Thermochemistry Experiment 8 Excercises

Question

A 19.80 mL solution of NaOH is required to titrate 0.6014 g KHP. How many mL of this NaOH solution required to titrate 25.0 mL of 0.10 M HCL solution? Show work!

Answer 1

KHP (potassium hydrogen phthalate) has the chemical equation of C₈H₅KO₄ and so the molar mass is calculated as:

C: 12.011 x 8 = 96.088

H: 1.008 x 5 = 5.040

K: 39.098 x 1 = 39.098

O: 15.999 x 4 = 63.996

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204.22 g/mol

NaOH (aq) + C₈H₅KO₄ (aq) → NaKC₈H₄O₄ (aq) + H₂O (l)

so it takes 1 mole of NaOH to neutralize 1 mole of the potassium hydrogen phthalate

The number of moles of KHP is calculated by using the molar mass as calculated above (204.22 g/mol)

(0.6014 g)/(204.22 g/mol) = 0.002945 moles

Therefore it takes 0.002945 moles of NaOH.

The molarity of the NaOH is (0.002945 moles)/(0.01980 liters) = 0.1487 moles/liter or 0.1487 M

Now, switch to the other reaction:

NaOH (aq) + HCl (aq) → NaCl (aq) + H₂O (l)

We are told that 25.0 mL of 0.10 M HCl is neutralized. To calculate the number of moles of HCl neutralized:

(0.025 liters)(0.10 moles/liter) = 0.0025 moles

Since the chemical reaction equation tells us that 1 mole of NaOH neutrlizes 1 mole of HCl, then 0.0025 moles of NaOH are needed.

(0.0025 moles)/(0.1487 moles/liter) = 0.01681 liters = 16.81 mL of the NaOH solution are needed