total alkalinity water test | phenolphthalein alkalinity | methyl orange alkalinity

Summary

This video provides a step-by-step guide on performing an alkalinity test on water, covering both phenolphthalein and methyl orange indicators. It details the required materials, preparation, titration process, and calculation of alkalinity in parts per million (ppm). The tutorial also explains how to interpret results using a table to determine hydroxyl, carbonate, and bicarbonate ion concentrations. Viewers learn how to identify the type and amount of alkalinity in a water sample, ensuring they can assess water quality effectively. The video concludes with practical examples and emphasizes typical drinking water alkalinity ranges for context.

Takeaways

• 😀 The video demonstrates how to perform an alkalinity test on water using phenolphthalein and methyl orange indicators.
• 😀 Required materials include 0.02 N HCl solution, 1% phenolphthalein and methyl orange indicators, a 50 mL beaker, conical flask, buret, funnel, dropper, and magnetic stirrer with bar.
• 😀 There are two types of alkalinity tested: phenolphthalein alkalinity (P) and methyl orange alkalinity (T).
• 😀 Phenolphthalein alkalinity is tested by adding phenolphthalein indicator to 50 mL of water and titrating with HCl until the pink color disappears.
• 😀 Methyl orange alkalinity is tested by adding methyl orange indicator to 50 mL of water and titrating with HCl until the water turns dark pink.
• 😀 The formula to calculate alkalinity in ppm is: volume of acid used (mL) × 10.
• 😀 In the example, phenolphthalein alkalinity was 25 ppm and methyl orange alkalinity was 196 ppm.
• 😀 A table can be used to determine the concentration of hydroxyl (OH⁻), carbonate (CO₃²⁻), and bicarbonate (HCO₃⁻) ions based on P and T values.
• 😀 For the given results, hydroxyl ions were 0 ppm, carbonate ions were 50 ppm, and bicarbonate ions were 146 ppm.
• 😀 Typical drinking water alkalinity ranges from 20 to 200 ppm, indicating that the tested water falls within normal limits.
• 😀 Proper use of magnetic stirring ensures homogeneous mixing during titration and accurate readings.
• 😀 Observing color changes carefully is crucial: pink for phenolphthalein, green and then dark pink for methyl orange, to determine endpoint accurately.

Q & A

What are the two types of alkalinity discussed in the video?

The two types of alkalinity are phenolphthalein alkalinity and methyl orange alkalinity.

Which indicators are used for testing phenolphthalein and methyl orange alkalinity?

Phenolphthalein alkalinity is tested using 1% phenolphthalein indicator, and methyl orange alkalinity is tested using 1% methyl orange indicator.

What is the initial volume of water sample used for both alkalinity tests?

50 milliliters of water sample is used for both phenolphthalein and methyl orange alkalinity tests.

What is the procedure to test phenolphthalein alkalinity?

Add 2–3 drops of 1% phenolphthalein indicator to 50 mL water. If the water turns pink, titrate with 0.02 N HCl using a buret until the color becomes colorless. Note the volume of acid used and calculate alkalinity using the formula: Volume of acid × 10.

How is methyl orange alkalinity determined?

Add 2–3 drops of 1% methyl orange indicator to 50 mL water. If the water turns green, titrate with 0.02 N HCl using a buret until the color turns dark pink. Note the volume of acid used and calculate alkalinity using the formula: Volume of acid × 10.

What were the observed volumes of HCl used in the experiment for phenolphthalein and methyl orange tests?

The volume of HCl used for phenolphthalein alkalinity was 2.5 mL, and for methyl orange alkalinity, it was 19.6 mL.

How are hydroxyl, carbonate, and bicarbonate ions determined from phenolphthalein and methyl orange alkalinity values?

Using the relationship between P (phenolphthalein) and T (methyl orange): if 2P < T, hydroxyl ion is absent, carbonate ion = 2P, and bicarbonate ion = T − 2P. Other conditions depend on the comparison of P and T values as explained in the table.

What were the calculated hydroxyl, carbonate, and bicarbonate ion concentrations in this experiment?

Hydroxyl ion = 0 ppm, carbonate ion = 50 ppm, and bicarbonate ion = 146 ppm.

What is the typical range of alkalinity in drinking water according to the video?

The typical alkalinity range in drinking water is between 20 and 200 ppm.

Why is a magnetic stirrer used during titration in this experiment?

A magnetic stirrer is used to ensure homogeneous mixing of the water sample and acid during titration, allowing accurate color change observation and precise measurement of alkalinity.

What does it mean if the phenolphthalein indicator does not change color when added to water?

If the phenolphthalein indicator does not change color, it indicates that the phenolphthalein alkalinity is zero and hydroxyl ions are absent.