Not usually. Potassium iodide is usually present in a large excess. It is usually the potassium iodate that is the limiting ingredient.
When an analyte that is a reducing agent is titrated directly with a standard iodine solution, the method is called "iodimetry". When an analyte that is an oxidizing agent is added to excess iodide to produce iodine, and the iodine produced is determined by titration with sodium thiosulfate, the method is called "iodometry".
Long story short, iodine in the solution made earlier through a reducing agent is weakly soluble and prone to loss to the air. Therefore, let's say you are using the titration to determine concentration of the titrant, the concentration would be off from the "true" concentration because you've lost some reactants.
THE PROCESS IS CALLED STANDARDIZATION OR CALIBRATION. It's called titration
This is far to be a rule for this titration.
If you're asking me to explain how Thiosulfate-Iodine titration works, I'll explain. Usually, this titration is used to calculate the amount of Iodide ions produced in a previous reaction, in order find the concentration of the substance reacted in that reaction. For example, in an attempt to find the percentage of Copper in a coin, the coin is first dissolved in concentrated Nitric acid, where Cu2+ ions are formed. Next, this solution is treated with excess Potassium Iodide solution. The reaction is: 2Cu2+ + 4I- ----> 2CuI + I2 The amount of Iodine liberated is then titrated with a known concentration of Sodium Thiosulfate solution. The reaction is: 2S2O32- + I2 ----> S4O62- + 2I-. Starch is used as indicator for this titration. The color at the end-point is bluish-black. From the volume of Thiosulfate required, the amount of Iodide ions can be calculated(using the second equation). From this, the amount of Copper can be calculated from the first equation. I hope this answers your question.
Because the iodine is liberated, hence it is called as iodometric titration.
hypo solution used in iodometric titration is sodiumthiosulphate. Its N\10 normality of Na2S2O3.
The end-point of the titration is more sharper if NH4CNS exist in the solution;
A thiosulfate titration is mostly carried out to determine the amount of iodine present in the solution. In these reactions, thiosulfate ion acts as the reducing agent. This types titrations are often called as 'iodometric titrations'.
It is used as indicator for the endpoint of a Iodometric (redox) titration: it gives a bluish grey to black color with very minute excess of Iodine-iodide ions (I3-)
In iodometry sodium thiosulphate is used because it is standardized by potassium dichromate and it is the best and relaible way to standardized sodium thiosulphate using iodometric titration. Infact sodium thiosulphate is also standardized by iodimetry. The difference between both of them is only of iodine. In iodometry iodine gas is liberated that will further react with sodium thiosulphate but in iodimetry standard solution of iodine is used.
yes
In formol titration, amino acids with formaldehyde are titrated with NaOH to measure the amount of amino acids in the solution. Potassium is also necessary for this titration and is supplied by using potassium oxalate. If calcium is present, it will react with the NaOH to form Ca(OH)2. This will make it appear to need more of the NaOH solution (and overestimate the titration). Potassium oxalate will chelate the calcium, and prevent it from reacting (forming calcium oxalate).
Because starch forms a dark blue colored soluble product with free iodine, so that the appearance of color in the solution from this reaction effectively shows when all the substances in the solution that react more strongly with iodine than does starch have been consumed and the titration is finished.
Method: titration with a standardized solution of sodium (or potassium) hydroxide.
Method: titration with a standardized solution of sodium (or potassium) hydroxide.
· In analytical chemistry, sodium thiosulphate is used for the determination of the strength of a given solution of iodine. · Sodium thiosulphate is preferred in iodometric analysis due to the fact that sodium thiosulphate is oxidized by iodine. It is also used to determine the strength of many oxidizing agents.