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#### Apps

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« on: July 05, 2024, 05:28:29 AM »
Hey. There is an experiment I am doing where I assume that a defect/contamination is happening due to the presence of some sodium carbonate in my solution.
The solution that I use is a mixture of sodium silicate solution and water in the ratio 1:2. I assume that the atmospheric carbon dioxide interacts with this sodium silicate solution to produce sodium carbonate inside the solution. Therefore I want to calculate the amount of sodium carbonate (if any) is present in this solution.
Is an acid-base titration to detect HCO3- and OH- useful in this case with HCl as titrant and double end point titration with phenolphthalein and methyl-orange indicators?
I tried this titration recently, however, in the second part the strength of NaOH is coming out to be almost 40g/L. But the qualitative analysis data sheet from the manufacturer of  the sodium silicate solution states that it contains onlz 14% NaOH.
Can someone help me with the procedure to be followed or the mistake in what I did?
The procedure I adapted is as follows : (from a different titration)

Aim of titration procedure I followed: To estimate the strength of Na2CO3 and NaOH in a given mixture by titrating against HCl
solution using two indicators method. You have been provided with ~ N/40 HCl solution. Prepare
Observations and Calculations:
Mass of Anhydrous Na2CO3 required for preparation of standard solution (~N/40):
Normality =
Molar mass of anhydrous Na2CO3 = 105.9888 g/mol
Equivalent mass of anhydrous Na2CO3 (a base) = = 52.9944 π
Amount of anhydrous Na2CO3 required to prepare N/40 standard solution =
g
g = 0.1325 g
Normality of standard sodium carbonate solution prepared =
= = = β¦β¦.. N
Step I) Preparation of Standard N/20 Sodium carbonate solution:
Mass of the clean and dry weighing bottle = W1 g = β¦β¦β¦. g
Mass of weighing bottle + anhydrous sodium carbonate = W2 g = β¦β¦β¦. g
Mass of weighing bottle after transferring sodium carbonate = W3 g = β¦β¦β¦. g
Mass of sodium carbonate transferred = (W2 β W3 ) g = W g = β¦β¦β¦. g
Normality of standard sodium carbonate solution prepared =
= = = β¦β¦.. N ------- Eqn 1
=
Step II) Standardization of the given HCl solution using standard Na2CO3 solution
Solution in burette: Given HCl
Solution in conical flask: Standard Na2CO3 solution (10 mL)
Indictor used: Methyl orange
Colour change at the end point: Yellow to red
Step III) To find the strength of Na2CO3 and NaOH in the given
mixture
Titration of given mixture of alkali against standardized HCl solution:
Solution in burette: Given HCl
Solution in conical flask: Given Mixture of Na2CO3 and NaOH (10
mL)Indictor used: (i) Phenolphthalein and (ii) Methyl orange
Colour change at the end point: (i) Pink to colourless and (ii) Yellow to red
Calculations:
Using the normality equation, ππ»ππππ»πΆπ = πNa2CO3(π π‘π) VNa2CO3(π π‘π)
Where,
From Table-I:
ππ»πΆπ = Volume of HCl used = β¦.. mL
VNa2CO3(π π‘π) = Volume of standard Na2CO3 solution used = 10 mL
= Normality of standard Na2CO3 solution
= = = β¦β¦.. N ------- (From Eqn 1)
β¦ Eqn 2
Normality of HCl = β¦β¦.. N
From Table-II:
Volume of HCl used with phenolphthalein as an indicator =
π1 = β¦β¦β¦β¦ = β¦β¦.. mL
Volume of HCl used with methyl orange as an indicator =
π2 = β¦β¦β¦β¦ = β¦β¦. mL
Thus, Volume of HCl used to neutralize NaOH and half of Na2CO3 β NaHCO3 = π1 mL
Volume of HCl used to neutralize NaOH and complete Na2CO3 = π2 mL
Volume of HCl used to neutralize half of Na2CO3 = (π2 β π1) ππΏ = β¦β¦. = β¦.. mL
Volume of HCl required to neutralize Na2CO3 completely = ππ»πΆπ = 2(π2 β π1) ππΏ = Vβ mL
Volume of HCl required to neutralize NaOH in the given mixture = π2 β 2(π2 β π1) ππΏ= VβmL
Using the normality equation π1 π1 = π2 π2,
I) πNa2CO3 (in mix) ππiπ₯π‘π’ππ = ππ»πΆπ πβπ»πΆπ
πNa2CO3 (in mix) = = N β¦β¦β¦ (Using Eqn 2) -------- Eqn 3
πNa2CO3 (in mix) = β¦β¦.. N
Strength of Na2CO3 in the mixture = π Na2CO3(in mix) Γ Equivalent mass of Na2CO3) g/L =
= g/L = g/L
Strength of Na2CO3 in the mixture = β¦β¦ g/L
II) πNaOH (in mix) ππiπ₯π‘π’ππ = ππ»πΆπ πββπ»πΆπ
Normality of NaOH in the mixture = = N β¦β¦ (Using Eqn 2) -------- Eqn 4
Strength of NaOH in the mixture = πNaOH (in mix) Γ Equivalent mass of NaOH g/L
= g/L = β¦ g/L
Strength of NaOH in the mixture =

#### Hunter2

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« Reply #1 on: July 05, 2024, 09:35:53 AM »
I think it's not possible to do in sodium silicate solution, because SiO2 will be precipitate, if acid is added.
What problems do you observe with your Silicate solution? Strong alkaline solution everything will absorb CO2.

Generally you can detect NaOH and Carbonate by using the two indicators

The consumption to  pH 4.5 Methylorange is the sum of both.
The consumption to pH 8.2 Phenolpthalein is the amount of NaOH + half of Carbonate. At that point bicarbonate still exising.
The Difference between times 2 is the amount of Na2CO3.

The description  you have shows to prepare some standard carbonate solutions. But do you need it?
You need only the factors for the normality for NaOH and Na2CO3.
« Last Edit: July 05, 2024, 10:50:48 AM by Hunter2 »

#### Apps

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« Reply #2 on: July 08, 2024, 06:46:20 AM »
I think it's not possible to do in sodium silicate solution, because SiO2 will be precipitate, if acid is added.
What problems do you observe with your Silicate solution? Strong alkaline solution everything will absorb CO2.

Generally you can detect NaOH and Carbonate by using the two indicators

The consumption to  pH 4.5 Methylorange is the sum of both.
The consumption to pH 8.2 Phenolpthalein is the amount of NaOH + half of Carbonate. At that point bicarbonate still exising.
The Difference between times 2 is the amount of Na2CO3.

The description  you have shows to prepare some standard carbonate solutions. But do you need it?
You need only the factors for the normality for NaOH and Na2CO3.

Thanks a lot for the reply.
no i do not require any standard carbonate solution to be prepared.
yes, I understand that this titration can be used to detect NaOH and carbonate.
However, in my case, I am not sure if any sodium carbonate are being formed in the solution. Although I got the strength to be around 11g/L.
I also tried bubbling some CO2 to this sodium silicate solution, and then titrated. the strength came out to be around 11g/L again. (I expected the value to be higher this time)
So now my conclusion would be that there is no sodium carbonate in the sodium silicate solution that I use? My first assumption was that atmospheric CO2 react with the sodium silicate solution to form some sodium carbonates in it.

also on adding HCl, I did not observe any SiO2 precipitate.. is it visible to naked eye? Could you please give me a chemical reaction for this process?

#### Hunter2

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« Reply #3 on: July 08, 2024, 06:59:47 AM »
Are you sure you have sodium silicate.
With any acid you will get
Na4SiO4 + 4 H+ => 4 Na+ + SiO2 + 2 H2O

And with your test with CO2, why should it higher, if you get Na2CO3 the NaOH or the silicate will drop. The amount of Na+ will not change.

https://en.m.wikipedia.org/wiki/Sodium_silicate

#### Apps

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« Reply #4 on: July 08, 2024, 09:23:56 AM »
I think there is some misunderstanding. I am sorry for my language. I will explain my problem again.

My original solution - sodium silicate (10mL) + water (20 mL). While using this solution for some of my experiments, there is some sort of contamination arising (cloudy milky appearance). The reason for this contamination is unknown. Therefore, one of my assumptions is that the contamination is from my sodium silicate solution. I assume that atmospheric carbon dioxide reacts with this sodium silicate solution to form sodium carbonate which now appears as the contamination.
Hence, I want to confirm the presence of this sodium carbonate in my sodium silicate solution and find out the amount using an acid base titration.
The titration I did was with HCl (titrant), and double endpoint with first phenolphthalein indicator and later methyl orange indicator on the same solution.

I got the strength of sodium carbonate as 11g/L and strength of NaOH as 40g/L.

Next I produced some CO2 (mixing citric acid and baking soda) and bubbled it into my original sodium silicate solution. Here I thought that this would accelerate my sodium carbonate presence. But again the strength of sodium carbonate came out to be around 11g/L in the new solution.

So now I infer that the atmospheric carbon dioxide may not have affected the sodium silicate solution at all. But where did the CO2 I bubbled go?
The question on original contamination still remains

#### Hunter2

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« Reply #5 on: July 08, 2024, 09:38:00 AM »
Quote
(cloudy milky appearance).

That is the SiO2 what precipitate this can be caused by CO2 or any other acid.
I am not sure you can detect Carbonate, because silicate will disturb the Analysis.

#### Apps

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