Preparation and Standardization of Na OH PDF

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Preparation and standardization of NaOH....

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Practical 1: Preparation and Standardization of sodium hydroxide SURNAME AND INITIALS: Fwamba R.M STUDENT NUMBER: 220102914 LABORATORY: LOCKER NUMBER:

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SIGNATURE: _________________________ DATE: __23 February 2021___

Preparation of sodium hydroxide solution and standardization of sodium hydroxide solution against potassium hydrogen phthalate

AIM

To prepare a sodium hydroxide solution. Then, to standardize the sodium hydroxide solution with the primary standard potassium hydrogen phthalate in the presence of phenolphthalein indicator using a massvolume titration.

REFERENCES

1.GH Jeffery, J Bassett, J Mendham and RC Denney, Vogel's Textbook of Quantitative Chemical Analysis, 5th ed., Longman Scientific and Technical, London, 1989, p. 292 – 293. 2.DA Skoog, DM West, FJ Holler and SR Crouch, Fundamentals of Analytical Chemistry, 9th ed., Brooks/Cole, USA, 2004, p. 385 – 387. 3.H Oosthuizen, Practical Manual for Analytical Chemistry Students, 2000, (Referred to as Green Book), p. 47 – 52. EQUATIONS

KH (C8H4O4)

(aq)

+ NaOH

(aq)

→ NaK (C8H4O4)

(aq)

+ H2O

(l)

REAGENTS

Potassium hydrogen phthalate solid, KH (C8H4O4) (AR) (Molar mass = 204.23 g mol−1) Sodium hydroxide solid, NaOH (ca. 0.1 M) Phenolphthalein indicator

PRELIMINARY CALCULATIONS 1. Mass of NaOH needed to prepare 250 mL of ca. 0.1 M NaOH solution (beaker) A minimum of 3 titrations need to be done. If a maximum of 50 mL NaOH will be used per titration, the total volume needed is 150 mL. 50 mL is needed as well for rinsing. So, I will prepare 250 mL.

mass NaOH = (0.1 mol NaOH/L) ×0.25 L × (39.997 g NaOH/mol NaOH) = 0.999925 g NaOH ≈ 1 g NaOH Dissolve 1 g NaOH solid with distilled water to a final volume of 250 mL (beaker).

2. Mass of potassium hydrogen phthalate needed to standardize 20 − 30 mL of ca. 0.1 M NaOH (m/v titration): 20 mL = 0.020 L 30 mL = 0.030 L

C

NaOH

= n NaOH ÷ V NaOH

n NaOH = C

NaOH

x V NaOH = 0.1 M x 0.020 L = 2.0 x 10-3 mol NaOH

n KH(C8H4O4) = n NaOH n KH(C8H4O4) = 2.0 x 10-3 mol KHP 204.23 g.mol-1 KHP x 2.0 x 10-3 mol KHP = 0.4085 g KHP

n NaOH = C

NaOH

x V NaOH = 0.1 M x 0.030 L = 3.0 x 10-3 mol KHP

n KH(C8H4O4) = n NaOH n KH(C8H4O4) = 3.0 x 10-3 mol KHP 204.23 g.mol-1 KHP x 3.0 x 10-3 mol KHP = 0.6127 g KHP Weigh between 0.4085 g and 0.6127 g of KHP accurately into a conical flask and dissolve in ca. 50 mL of distilled water.

FLOW CHART Weigh 0.4085 g – 0.6127 g KHP accurately into a numbered conical flask (x3). Record the mass in table 2.

Weigh ca. 1 g NaOH(s) and dissolve with distilled water to a final volume of 250 mL. Record the weighed mass in table 1.

Dissolve in 50 mL of distilled water.

Burette : ca. 0.1 M NaOH.

Add 1-2 drops of phenolphthalein indicator. Titrate

Titrate until a colour change from colourless to light pink occurs. Complete table 3 and calculate the concentration of NaOH.

RESULTS Standardization of sodium hydroxide against potassium hydrogen phthalate. Equation: KH (C8H4O4) (aq) + NaOH (aq) → KNa (C8H4O4) (aq) + H2O (l) Table 1. Mass of NaOH weighed out. Mass of vial + NaOH

Mass of vial

Mass of NaOH

(g)

(g)

(g)

[NaOH] =

M

Table 2. Masses of potassium hydrogen phthalate weighed out.

Mass of vial + salt (g)

Mass of vial

Mass of salt

(g)

(g)

1. 2. 3. 4. 5. 6.

Table 3. Volumes of NaOH titrated against sodium hydrogen phthalate.

Mass of

Initial

Final

Volume of

x

KH(C8H4O4)

burette

burette

NaOH

(M)

reading

reading

(mL)

(g)

(NaOH)

(NaOH)

[NaOH]

(mL)

(mL)

(M)

1. s (M)

2. 3.

CV (%)

4. 5. 6.

[NaOH] =

M

FINAL CALCULATIONS

Standardization of ca. 0.1 M NaOH with KHP NaOH mol: KHP mol 1:1 Therefore, number of moles of KHP= number of moles NaOH Equation: [NaOH]1 = (mass KHP1 (g) ÷ 204.23 g.mol-1 KHP) = mol ÷ V(NaOH)titrated 1 (L) = M (mol/L) NaOH [NaOH]1 = = =

g KHP1 ÷ 204.23 g.mol-1 KHP mol ÷ L (NaOH)titrated 1 M NaOH

[NaOH]2 = = =

g KHP2 ÷ 204.23 g.mol-1 KHP mol ÷ L (NaOH)titrated 2 M NaOH

[NaOH]3 = = =

g KHP3 ÷ 204.23 g.mol-1 KHP mol ÷ L (NaOH)titrated 3 M NaOH

Avg. [NaOH] = ________________ M (mol/L)

CONCLUSION

Discuss the precision of your experiment by mentioning the CV value. A low CV indicates good precision, whereas a high precision indicates low precision. Say what could’ve been done differently or additionally to get more accurate results....