Improve this chart| Accuracy| Precision|
Definition:| The degree of closeness to true value.| The degree to which an instrument or process will repeat the same value.| Measurements:| Single| Multiple measurements are needed| About:| A term used in measuring a process or device.| A term used in measuring a process or device.| Uses:| Physics, engineering, statistics etc.| Physics, engineering, statistics etc.| http://www.diffen.com/difference/Accuracy_vs_Precision
Example: One can say that a measurement is accurate but not precise; precise but not accurate; neither or both. An example of bad precision and good accuracy can be: Suppose a lab refrigerator holds a constant temperature of 38.0 F. A temperature sensor is tested 10 times in the refrigerator. The temperatures from the test yield the temperatures of: 37.8, 38.3, 38.1, 38.0, 37.6, 38.2, 38.0, 38.0, 37.4, 38.3. This distribution shows no impressive tendency toward a particular value (lack of precision) but each value does come close to the actual temperature (high accuracy).
In the Iodometry, this is based on the oxidation of iodide into iodine. Iodometry is used for determine the amount of oxidizing agents. The amount of oxidizing agent is determined by titration of iodine with thio sulfate. Starch is used as indicator. The end point detection is based on the formation of blue starch complex. Iodometric titration (oxidation of iodide) is done in two steps.
The first step is done by the reaction between the oxidizing agents (KMnO4, K2Cr2O7, CuSO4, peroxides etc) and KI (excess) in neutral or in weak acidic medium. Thus the iodine is quickly liberated.
KI + Oxidizing agent → I2 (or)
2I- ↔ I2 + 2e-
K2Cr2O7 + 6KI + 7H2SO4 → Cr2 (SO4)3 + 4K2 SO4 + 7H2O + 3I2 Second step
In this step, the liberated iodine (in first step) is titrated with standard solution of sodium thiosulfate. Starch is used as indicator. At the end point, the blue or violet color of starch indicator disappears due to change of iodine to iodide. So the titration in which liberated iodine (from potassium iodide) is titrated with a standard solution of sodium thiosulfate is known as iodometric titration. Thus the chemical reaction is I2 + Na2S2O3 → 2NaI + Na2S2O4
2S2O32- + I2 → S4O62- + 2I-
This is the principle reaction which shows the reduction of iodine. Thus the halogens, oxy halogens, cupric ions, peroxides, sulfur dioxide in food industry etc can be...