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Questions tagged [titration]

A laboratory method to determine the concentration of an analyte in solution. The solution volume plays a key role in the analysis.

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17
votes
2answers
17k views

Why is a theoretical titration curve higher than a practical one?

I'm currently in high school and I did two titrations. The first one is a titration of $10.0~\mathrm{mL}$ $0.1~\mathrm{M}$ $\ce{HCl}$ with $x~\mathrm{mL}$ $\ce{NaOH}$. I obtained the following ...
12
votes
2answers
1k views

Why are synthetic pH indicators used over natural indicators?

Synthetic indicators seem to be exclusively used when determining the pH of a substance with an indicator (with the exception of that school experiment where you boil cabbage to demonstrate natural pH ...
12
votes
1answer
1k views

How to analyze a acid and salt mixture using titrimetry?

Given a mixture of $\ce{HCl}$ and $\ce{MCl3}$ and the following dissociation constants for $\ce{M(OH)3}$, how can the concentrations of $\ce{HCl}$ and $\ce{MCl3}$ be determined separately by titrating ...
11
votes
4answers
51k views

Shouldn't the pH at the equivalence point always be 7?

I learned in class that the equivalence point in an acid-base titration is reached when the solution contains an equal amount of substance of $\ce{OH-}$ and $\ce{H+}$ ions. However, in a weak acid and ...
11
votes
1answer
4k views

Why is Borax used as a primary standard?

It's given in my book that borax is a useful primary standard for titrating against acids. I have heard that primary standard is a pure reagent and does not gain any weight by absorbing moisture. (...
10
votes
2answers
567 views

Use of pipette during experiments for determination of oxygen by Winkler's method

We were performing estimation of $\ce{O2}$ by Winkler's method and we were told by the instructor that while adding $\ce{MnSO4}$ and $\ce{NaOH}$ / $\ce{KI}$ the pipette tip should be well below the ...
9
votes
2answers
844 views

What are the limitations of the Hendersson-Hasselbalch equation?

Our instructor told us that prior to the equivalence point, the $\mathrm{pH}$ of a solution is dependent on the HH equation. However, when I tried practicing for polyprotic acid titration, I came upon ...
9
votes
2answers
4k views

Find the initial volume of the weak acid given a titration graph

Question: Below is a picture of a titration between a weak acid, $\ce{HA}$, and a 0.150 M $\ce{NaOH}$ solution. Find the initial volume of the weak acid in milliliters in this titration. My ...
9
votes
3answers
17k views

How do we calculate N factor and why is it useful in calulations?

I don't understand the concept of N factor at all. Why is it important? I know that it is something dependent upon the oxidation number, for example N factor of Na would be 1 since it has oxidation ...
8
votes
3answers
39k views

Calculating Buffer Capacity

I completed a titration of Ammonium Acetate buffer solution and to it I added $\pu{2M}$ Hydrochloric Acid. I measured the initial $\ce{pH}$ of the buffer solution before any acid was added and I ...
8
votes
2answers
22k views

Why are strong acids and bases not suitable as primary standards?

This is one of the questions with which I have puzzled over, and can arrive at no definite conclusion. Why are strong acids or bases, such as $\ce{H2SO4}$,$\ce{ HNO3}$, $\ce{HCl}$, and $\ce{NaOH}$ not ...
8
votes
2answers
313 views

What is the meaning of cmmol in chemistry?

I came across a unit called $\text{cmmol dm}^{-3}$ in buffer solutions. What does this unit mean?
8
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3answers
39k views

Volume required to dilute solution for a pH change

A $\pu{100 mL}$ solution of $\ce{NaOH}$ has a $\mathrm{pH}$ of $13$. What volume of water in $\pu{mL}$ must be added to change the $\mathrm{pH}$ to $11$? My steps: Begin by calculating conc. of $[\...
8
votes
1answer
33k views

How do I calculate the concentration of sulphuric acid by a titration experiment with sodium hydroxide?

In my latest chem lab the objective was to create a primary standard of $\ce{NaOH}$ and use it to determine the concentration of sulfuric acid. The first part of the lab was determine the molarity of ...
8
votes
1answer
234 views

Why do these two calculations give me different answers for the same acid-base titration?

In class, I performed an weak acid-strong base titration using commercial white vinegar and sodium hydroxide with the aim of finding the concentration of of ethanoic acid in the vinegar, and I used ...
7
votes
1answer
3k views

Why does phosphoric acid mask the colour of iron(III) complex in water?

In the redox titration of iron(III) with permanganate or dichromate, we use phosphoric(V) acid to "mask" the color of iron(III) because it interferes with the end point color change. What's the ...
7
votes
1answer
2k views

Why must NaOH be kept dry during storage?

Why should the Erlenmeyer flask used to store $\ce{NaOH}$ be dry? Why should it be kept covered at all times?
7
votes
2answers
31k views

Amount of Phenolphthalein required

We just had chemistry practical few days a go. The topic was strong acid-base titration, in which we had to find the normality and concentration of $\ce{HCl}$. My teacher instructed me to add 2 drops ...
7
votes
3answers
3k views

Is the Henderson–Hasselbalch equation volume independent?

Looking at this equation $\mathrm{pH} = \mathrm{p}K_\text{a} +\log\frac{[\ce{CB}]}{[\ce{A}]}$ makes me think that it is concentration independent. What I mean is, when we look at $\frac{[\ce{CB}]}{[\...
7
votes
1answer
104 views

How did early chemists measure concentrations and purity?

My chemistry teacher loves going back through the history of famous chemists. This got me wondering how these chemists would first determine the concentration of a sample before they had any other ...
7
votes
1answer
557 views

How can one optimise the formation of copper acetate?

Mixing solid copper, $5\%$ vinegar, and hydrogen peroxide ($\ce{H2O2}$) causes copper acetate to form. The process will occur very slowly without hydrogen peroxide. Adding $\ce{H2O2}$ speeds the ...
7
votes
2answers
1k views

Brown color at end point during titration with phenolphthalein as indicator

We did a titration experiment at school and I did not understand one part of it. The scenario: Titrate : White wine (ethanoic acid) Titrant: $\ce{NaOH}$ Indicator: Phenolphthalein What happened:...
7
votes
1answer
235 views

How to derive the conductivity titration curve which accounts for salt formation

I derived an equation that gave me the volume of base required to get a certain $\mathrm{pH}$: In a titration between a weak acid $\ce{HA}$ and weak base $\ce{B}$ (adding base into acid solution) the ...
7
votes
2answers
2k views

Weighing by difference

When preparing a known mass of something (e.g. when producing a standard solution) it is often that in my school lab that we first use a weighing boat to measure the mass and then once transferred ...
7
votes
1answer
12k views

Sodium carbonate titration in presence of phenolphthalein

Why phenolphthalein cannot show the endpoint for the complete titration of Na2CO3 with only phenolphthalein? What's the reason that we consider only half of the moles of sodium carbonate when ...
6
votes
1answer
8k views

Why, in titration, is universal indicator not commonly used?

My teacher said that we always used indicators such as methyl red, methyl orange, litmus, phenolphthalein, etc. rather than universal indicator. I don't understand why, though, would not universal ...
6
votes
1answer
3k views

How is the the law of chemical equivalence defined and what are its limitations?

I've heard that the law of chemical equivalence states that the gram equivalence of each of the reactants equals the gram equivalence of each of the products. But I'm facing difficulties in ...
6
votes
1answer
102 views

How much additional hydrochloric acid should be added to arrive at ‘excess acid’?

I am an IB student. And I am trying to find the mass percentage of $\ce{NaHCO3}$ in antacid. I am dissolving the antacid in $\pu{0.1 M}$ $\ce{HCl}$ solution. So, first of all I conducted some ...
6
votes
2answers
682 views

How to calculate the concentration of conjugate acid from given pH and pKa values?

Preface: Buffer solution (acid-base buffer). I am provided with a weak base, which I will designate B. $\mathrm{p}K_\mathrm{a}$ for $\ce{B}$'s conjugate acid, which I will designate $\ce{BH}$, is $8.1$...
6
votes
2answers
7k views

What is causing the buffer region in a weak acid - strong base titration?

For the buffer region in this, why does it stop the pH from increasing? At the start: $$\ce{CH3COOH + NaOH -> CH3COONa + H2O}$$ Which means there will be a high amount of salt in the solution, ...
6
votes
1answer
4k views

Buffer formation in weak acid/strong base titration?

I'm a little confused about what happens when you titrate a weak acid or base. For example, let's say that you are trying to titrate a weak acid. Based on this question, it seems like the weak acid ...
6
votes
1answer
617 views

What would one have to do differently if they used NaMnO4 instead of KMnO4 for redox titrations?

I am doing a chemistry report related to redox titrations (using $\ce{KMnO4}$ as the titrant), and one section of the report asks me to explain what would occur if I were to use sodium permanganate ($\...
6
votes
1answer
1k views

Which method can be used to determine the pKa of an acid-base indicator like bromothymol blue?

I have a question about how one would determine the pKa of an acid-base indicator such as bromothymol blue. I know that spectrophotometric analysis is one option, but is it possible to perform an ...
6
votes
3answers
8k views

Why the colour of KMnO4 at the end point of titration may disappear after some time?

In the redox titration of $\ce{FeSO4}$ with $\ce{KMnO4}$, the colour change of the solution at the end point is colourless to light pink. Most laboratory manuals and books advice us to check whether ...
5
votes
5answers
83k views

What role does sulfuric acid play in the titration of oxalic acid and potassium permanganate?

The titration is between oxalic acid and potassium permanganate, with $\ce{H2SO4}$ added to oxalic acid. My question is what role other than a dehydrating agent and maybe catalysing does the $\ce{...
5
votes
1answer
69k views

Why is phenolphthalein an appropriate indicator for titration of a strong acid with a strong base?

How does the pH at the equivalence point, as well as the pH range over which the colour of phenolphthalein changes, make it a suitable indicator for titrations between strong acids and strong bases?
5
votes
2answers
104 views

Should the tip of the burette of an automatic titrator be immersed in the analyte?

In all the tutorials I found online, the tip of the burette (containing the titrant - NaOH) was immersed into the analyte solution. My question is: shouldn't the tip be out of the solution? Isn't ...
5
votes
1answer
705 views

NaOH Normality Slowly Changing

Our lab uses a sodium hydroxide solution of a (theoretically) known normality (0.8000 - 1.0000) to titrate product samples for quality control. However, we suspect that the normality of the $\ce{NaOH}...
5
votes
1answer
662 views

How to get a precise reading from pipette?

While doing titrations, we are instructed to use pipette and they demonstrated how to use a pipette. But still after all this, we face difficulties of how to take precise reading from pipette. ...
5
votes
2answers
3k views

What are the products for the redox reaction HCl + SnCl₂ + KMnO₄?

In the redox reaction, where $\ce{HCl}$ is the excess reactant do these reactions produce following half reactions? \begin{aligned} (1)&&\ce{SnCl2 &-> Sn^{4+} + 2e-}\\ (2)&&\ce{...
5
votes
1answer
2k views

Yellowish tinge during titration of oxalic acid with potassium permanganate

One of the our chemistry practicals involve finding the molarity of an oxalic acid solution by titrating it with standard $\ce{KMnO4}$ solution. The oxalic acid solution is heated and little sulfuric ...
5
votes
1answer
19k views

No indicator is suitable when titrating weak acid with weak alkali

This was a statement in my book: A solution of a weak acid cannot be titrated with a weak base using an indicator to find the end-point because the pH change is too gradual close to the equivalence ...
5
votes
1answer
2k views

The significance of the dissociation constant of an indicator

In the chapter acid-base, I learned about indicators and how they are actually weak acids. This is the equation given in our book: $\ce{HIn + H_2O <=> H_3O^+ + In^-}$ $K_{in}= \left(\frac{[\...
5
votes
1answer
1k views

How to calculate the dissociation constant of a weak acid from the titration with a strong base?

Problem: A solution of an unknown weak acid of unknown concentration was titrated with a solution of a strong base of unknown concentration. During the titration, the pH after adding $\pu{2.00 mL}$ ...
5
votes
1answer
8k views

Deriving the equation for oxygen estimation by Winkler’s method

We were doing $\ce{O2}$ estimation by Winkler's method The procedure and reactions involved in this experiment are: Carefully fill a 300-mL glass stoppered bottle brim-full with sample water. ...
5
votes
2answers
6k views

How can I choose an indicator for determining the concentration of a base using its pKb values?

I have a base $\ce{M(OH)_{3}}$ having 3 $\mathrm{p}K_{\mathrm{b}}$ values as, $$ \mathrm{p}K_{\mathrm{b}_{1}} = 0.5\\ \mathrm{p}K_{\mathrm{b}_{2}} = 3.7\\ \mathrm{p}K_{\mathrm{b}_{3}} = 7.7\\ $$ If a ...
5
votes
1answer
829 views

What does it mean to take reading up to 0.05 mL?

In titration we usually take burette reading upto $0.01~\mathrm{mL}$, but my teacher says that we need to take reading up to $0.05~\mathrm{mL}$. What does that mean? Does it mean if I read $23.56~\...
5
votes
1answer
642 views

Iodometric titration of copper – standard electrode potentials

Upon inspection of the standard electrode potentials for the half reactions for both $\ce{Cu^2+}$/$\ce{Cu+}$ and $\ce{I2}$/$\ce{2I-}$, it becomes apparent it should be the iodide ions that act as the ...
5
votes
1answer
58 views

How do you experimentally calculate the ionization constant of the carbonate ion?

Given sodium hydrogen carbonate, $\ce{NaHCO3}$, as well as hydrochloric acid, $\ce{HCl}$, how would you experimentally determine the ionization constant for the carbonate ion, $\ce{HCO3-}$? By ...
5
votes
2answers
341 views

Find second acid dissociation constant at a given pH

In short, the problem states that: We have a molecule that has two ionizable groups $\mathrm{p}K_\mathrm{a,1}$ is between $5.0$ and $9.0$; $\mathrm{p}K_\mathrm{a,2}$ is outside of this range. ...