What inert materials are likely to be present in chalk, and what other indicator can be used in place of methyl orange

The chemical composition of chalk is calcium carbonate, with minor amounts of silt and clay.[1] It is formed in the sea by sub-microscopic plankton, which fall to the sea floor and are then consolidated and compressed during diagenesis into chalk rock. Phenolpthalein is a classical pH indicator at mid range, https://www.youtube.com/watch?v=jEvhhxg2yKA

Note that different reactions take place with methyl orange vs phenolphthalein.

With methyl orange it is CO3^2- + 2H^+ ==> H2O + CO2
With phenolphthalein it is CO3^2- + H^+ ==> HCO3^-

To identify the inert materials present in chalk, you can perform a simple experiment using vinegar (dilute acetic acid). Here's how you can proceed:

1. Take a small piece of chalk and crush it into fine powder.
2. Pour vinegar into a container.
3. Add the powdered chalk into the vinegar.
4. Observe any changes that occur.

When chalk reacts with vinegar, a chemical reaction takes place. The carbonates present in chalk (usually calcium carbonate, CaCO3) react with vinegar (acetic acid, CH3COOH) to form carbon dioxide gas (CO2), water (H2O), and a salt called calcium acetate (Ca(CH3COO)2). The effervescence you observe is due to the release of carbon dioxide.

The inert materials in chalk are typically impurities that are non-reactive or have limited solubility in vinegar. These might include small amounts of silica (SiO2) and other minerals that are not affected by the vinegar.

Regarding the replacement of methyl orange as an indicator, typically methyl orange is not used in chalk experiments or tests. Methyl orange is commonly used as an acid-base indicator, with its color changing from red in acidic solutions to yellow in basic solutions. Chalk experiments generally focus on its interaction with acids, and the observation of effervescence from carbon dioxide release is sufficient for identification purposes.

However, if you still want to use an indicator to test the acidity or basicity of a solution, you can consider using universal indicator paper or a solution of phenolphthalein indicator instead of methyl orange. Universal indicator paper provides a range of colors that correspond to different pH values, while phenolphthalein changes from colorless to pink in basic solutions.