POTENTIOMETRIC ANALYSIS OF TIN (Sn) PLATING BATHS

Potentiometric analysis of tin (Sn) plating baths

Summary
Potentiometric titration methods for the analysis of acid and alkaline tin plating baths are presented. Following methods are described: tin(II) / tin(IV) / total tin, free fluoroboric acid or free sulfuric acid, chloride in acidic tin baths, free hydroxide and carbonate in alkaline tin baths.

Apparatus and accessories
• Titrino or Titrando with Dosino or Dosimat
• Magnetic swing-out stirrer
• Exchange unit(s)
• Pt Titrode 6.0431.100 with electrode cable 6.2104.020
• Comb. pH glass electrode 6.0255.100
• Ag Titrode with Ag2S coating 6.0430.100

Reagents
These are described under the individual analyses.

1. Iodometric tin determination
To increase the accuracy of this analysis, 10.0 mL bath sample is pipetted into a 100 mL graduated flask, filled up to the mark with distilled water and mixed well.

Reagents:
• c(Iodine solution) = 0.05 mol/L
• w(HCl) = 36%
• Iron powder p.a.

1.1. Tin(II)
Add 15 mL HCl and 50 mL dist. H2O to 10.0 mL diluted sample (corresponding to 1 mL original bath) in a beaker and titrate with c(iodine solution) = 0.05 mol/L against the Pt Titrode.








Application Bulletin No. 90/2 e
Potentiometric analysis of tin plating baths Page 2

1.2. Tin(IV) and total tin
In compliance with the tin content, pipet between 10.0 - 50.0 mL of the diluted sample (1 - 5 mL original bath) into a wide-necked Erlenmeyer flask and add 50 mL HCI. Stirring well, add ca. 1 g iron powder in small portions and when reaction subsides, warm up until the iron powder is entirely dissolved. Cool immediately and titrate with c(iodine solution) = 0.05 mol/L against the Pt Titrode.

Calculations:
1 mL c(Iodine solution) = 0.05 mol/L = 5.9345 mg Sn

Sn = EP1 x C01 / C00 ;2; g/L

C00 = sample size in mL original bath = 1 mL
C01 = 5.9345

Answer

Sn = 3.03 x 5.9345 / 1 = 17.98 g/L

Where
EP1 = 3.03 mL


Application Bulletin No. 90/2 e
Potentiometric analysis of tin plating baths Page 3

2. Free fluoroboric acid or free sulfuric acid
Reagents:
• c(NaOH) = 1 mol/L
• Sodium sulfate p.a.

Analysis:
Dilute 10.0 mL bath sample to approx. 50 mL with dist. H2O in a beaker. While stirring dissolve approx. 5 g Na2SO4 and titrate afterwards with c(NaOH) = 1 mol/L against the comb. pH glass electrode. The flat potential jump at pH = approx. 3.2 is evaluated.


Calculations:
1 mL c(NaOH) = 1 mol/L = 87.81 mg HBF4 or 49.037 mg H2SO4

HBF4 = EP1 x C01 / C00 ;2; g/L
H2SO4 = EP1 x C02 / C00 ;2; g/L

C00 = Sample size in mL original sample = 5 mL
C01 = 87.81
C02 = 49.037

Answer

HBF4 = 9.932 x 87.81 / 5 = 174.43 g/L
H2SO4 = 9.932 x 49.037 / 5 = 97.41 g/L

EP1 = 9.932 mL

3. Chloride determination in acidic tin baths

Reagents:
• c(AgNO3) = 0.1 mol/L
• w(HNO3) = 65%

Application Bulletin No. 90/2 e
Potentiometric analysis of tin plating baths Page 4

Analysis:
Pipet 1.0 mL bath solution into a beaker and dilute to approx. 50 mL with dist. H2O. Add 2 mL HNO3 and titrate with c(AgNO3) = 0.1 mol/L against the Ag Titrode (Ag2S-coating).

Calculations:
1 mL c(AgNO3) = 0.1 mol/L = 3.5453 mg Chloride

Chloride = EP1 x C01 / C00 ;2; g/L

C00 = sample size in mL original bath = 1 mL
C01 = 3.5453

Answer

Chloride = 3.473 x 3.5453 / 1 = 12.31 g/L

EP1 = 3.473 mL


4. Free hydroxide and carbonate in alkaline baths

Reagents:
• c(HCl) = 1 mol/L
• w(BaCl2) = 25%

Analysis:
Add 50 mL BaCl2 to 10.0 mL bath sample in a wide-necked Erlenmeyer flask and boil for a short time. Allow to cool and slowly titrate the still warm solution with c(HCl) = 1 mol/L against the comb. pH glass electrode.

Calculations:
Two endpoints are obtained. The consumption up to EP1 corresponds to NaOH, between EP1 and EP2 to tin and between EP2 and EP3 to carbonate.

1 mL c(HCl) = 1 mol/L = 40.0 mg NaOH or 106.0 mg Na2CO3

NaOH = EP1 x C01 / C00 ;2; g/L
Na2CO3 = (EP3 - EP2) x C02 / C00 ;2; g/L

C00 = Sample size in mL original sample =10 mL
C01 = 40
C02 =106

Answer

NaOH = 6.911 x 40 / 10 = 27.54 g/L
Na2CO3 = (14.329-11.657) x 106 / 10 = 28.32 g/L

EP1 = 6.911
EP2 = 11.657
EP3 = 14.329

Literature
Metrohm, Application Bulletin No.90/2e