During the determination ofCaCO3 in chalk content by back titration.
a_what inert materials are likely to be present?
b_suggest other suitable indicators of the reaction.
https://www.jiskha.com/questions/1806082/What-inert-materials-are-likely-to-be-present-in-chalk-and-what-other-indicator
To determine the CaCO3 content in chalk using a back titration, it is important to consider inert materials that may be present in the analysis. Inert materials are substances that do not react chemically with the reagents involved in the analysis. These materials can interfere with the accuracy of the results if not accounted for.
a) In the case of chalk, the most common inert materials that may be present are:
1. Silica (SiO2): This is a common impurity in chalk, which is chemically inert and does not react with the reagents used in the analysis.
2. Clay minerals: Chalk sometimes contains clay minerals, like montmorillonite or kaolinite, which do not react with the reagents.
3. Metal oxides: Small amounts of metal oxides, such as iron oxide (Fe2O3) or aluminum oxide (Al2O3), may also be present as impurities in chalk. These materials are inert as well.
b) When it comes to choosing suitable indicators for the reaction, an indicator is used to determine the endpoint of a titration by changing color at or near the equivalence point. In the case of back titration for CaCO3 determination, the commonly used indicator is phenolphthalein, which changes from colorless to pink at a pH of around 9-10.
However, if phenolphthalein is not suitable or available, other indicators that can be used include:
1. Methyl orange: This indicator changes color from red to orange or yellow at a pH of around 4.4-6.2. Although not as commonly used as phenolphthalein, it can be applicable if the reaction conditions permit.
2. Bromothymol blue: This indicator changes color from yellow to blue at a pH of around 6.0-7.6. This indicator could be used if the reaction is carried out at a higher pH than the range of phenolphthalein.
3. Thymol blue: This indicator changes color from red to yellow at a pH of around 8.0-9.6. It can be used if the reaction pH is higher than the range of phenolphthalein but lower than methyl orange or bromothymol blue.
It is important to note that the choice of the indicator depends on the specific reaction and conditions in the back titration, so it's always essential to consider the pH range and the reaction characteristics when selecting an indicator.