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1.1

Minor Versionm

by Procheta Mallik

Introduction

The simplest acid/base indicator tests involve a colour-change. Here we perform a classic test using bromothymol blue on an acidic and basic solution and then perform a titration to measure the concentration of the acid/base.

    • Care should be taken while adding HCl.

    • Do not ingest any materials

    • Wash hands thoroughly after conducting the experiment

    This guide needs various editing from you first: spelling of chemicals, some changes in materials and/or alternate instructions based on the actual materials we’ll give kids etc.

    Procheta Mallik - Reply

  1. Take out the given lime (calcium oxide).
    • Take out the given lime (calcium oxide).

    • Pour 200ml of water in a transparent container.

    • Mix the lime thoroughly in the water

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    • Using a dropper/syringe, pour 5ml of the lime-water solution (calcium hydroxide) into another transparent container

    • Make sure to clean out the dropper/syringe with water

    • Add 5-6 drops of bromothymol blue to the above container.

    • Stir it well; you should observe a dazzling blue colour solution .

    Same problem here. It needs to be Ca(OH)2 in the picture as well

    Procheta Mallik - Reply

    • Take out the bottle containing HCl.

    • Pour all of it into a third transparent container

    • Draw some of the HCl to fill the dropper/syringe.

    I can change the `L’ in the text, but can’t in the picture, which you will have to do. L should not be capital. Has to be HCl.

    Procheta Mallik - Reply

    • From the dropper/syringe, add the HCl drop by drop into the container containing the calcium hydroxide solution.

    • Observe the colour change .

    • You may/will need to keep filling up the dropper/syringe multiple times before you see the colour change. Keep a note of this. Please note the volume of HCl that was required to change the colour

    Again, HCl will be added directly from the dropper and not a syringe. Pictures and instructions have to reflect that

    Procheta Mallik - Reply

    • Make sure you add HCl drop by drop and stir well.

    • Measuring of HCl should be accurate.

    • There should be no spillage of acid or base

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    • Calculate the concentration of the HCl solution?

    • Sample calculation and some required data are given in the next step

    • Find the molar mass of Ca(OH)2 and HCl

    • Write down the neutralisation chemical reaction happening in this experiment

    • At what point does neutralisation occur? I.e. how many moles of HCl are required to neutralise 1 mole of Ca(OH)2?

    • If the volume of Ca(OH)2 is 10ml, what will be the concentration of HCl if 5ml of HCl neutralises the solution?

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    • Molar mass of Ca(OH)2 = 74.093g/mol

    • Maximum solubility of lime in water at room temperature is 1.7g/l. Since we have given 1g for 200ml of water, we reach the maximum molarity of 0.02moles/litre for Ca(OH)2.

    • For your calculation, use molarity of Ca(OH)2 = 0.02moles/litre.

    • In our sample calculation, we will assume molarity of Ca(OH)2 = 0.01M and that we needed 5ml of HCl to neutralise the solution

    • From the chemical equation we know that C1V1=2C2V2, where C1 is concentration of Ca(OH)2 and V1 is volume of Ca(OH)2. C2 is concentration of HCl and V2 is volume of HCl.

    • By applying the above formula , C2 = C1V1/ V2 i.e,

    • Concentration of HCl = 0.01M X 5ml / 20 ml = 0.0025M

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Vishal Bhatt

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