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We are aiming to accurately prepare a standard solution of 0.1 M (mol dm-3) sodium carbonate; this solution will then be used to calculate the concentration of a hydrochloric acid solution

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Introduction

´╗┐Serena Wright Gardner Titration Aim A common practise carried out in the laboratory is to accurately prepare chemical solutions. We are aiming to accurately prepare a standard solution of 0.1 M (mol dm-3) sodium carbonate; this solution will then be used to calculate the concentration of a hydrochloric acid solution. Background The most convenient ways to express concentration is in: g dm-3 grams per cubic decimetre or grams per litre mol dm-3 the number of moles per cubic decimetre For measuring accurately, you will use equipment like pipettes, burettes and volumetric flasks. Experiment 1 Making a solution of sodium carbonate (alkali) by weighing Below is the standard procedure that I followed I copied and pasted it into my work: Calculate the mass of sodium carbonate needed, m1. Weigh a clean weighing bottle, and record its mass, m2. (See figure a) With a clean spatula, add pure anhydrous sodium carbonate until the combined mass of weighing bottle and sodium carbonate = m1+m2. Transfer the sodium carbonate carefully into a clean beaker. (See figure b) Use a washed bottle of distilled water so that all the washings run into the beaker. Add about 100 cm3 of distilled water. Stir with a glass rod until the entire solid has dissolved. (See figure c) ...read more.

Middle

The method uses a titration in which an acid is added to a base, until there is just enough of the acid to neutralise the base. An indicator tells when exactly the right volume of solution has been added to achieve neutralisation. When the concentration of the acidic and basic complexes of the indicator is equal, the indicator is said to be at its end point. The amount of acid it takes to neutralise the base is recorded. The concentrations of one of the two solutions must be known, and the volumes of both must be measured. You can use a standard solution of a base to find out the concentration of a solution of an acid. You have to find out what volume of the acid solution of unknown concentration is needed to neutralise a known volume, usually 25.0cm3, of the standard solution of a base. ________________ Method Use a pipette to deliver 25.0cm3 (V2) of the alkali solution into a clean conical flask Add a few drops of indicator. (The alkali solution in this experiment is the standard solution you made up of 0.1M Sodium Carbonate (M2) ) Wash the burette with a little of the acid solution. Allow the solution to run into the tip of the burette. Read the burette (from the bottom of the meniscus) and record this ?initial volume of acid? in the results table) ...read more.

Conclusion

The accuracy of my calculation was quite good, as my predictions never went above 25.6 (first 25.6, second 25.4, third 25.3). Problems with experiment For some of the results I did not turn off the tape at the exact time that it changed colour, which would make it not a far test. There were some problems that were not my fault; such as I could not turn off the tape some times, which made it difficult to get a correct reading. I also may not have filled the burette to exactly 50cm3, which means that it would have taken more solution to get to the correct reading. When I put the 50cm3 of solution into the burette I could not clearly see the line, and I may have not read off the reading from the meniscus line. I did not stop pouring out the solution at exactly the same time it changed colour, and so this would make readings out. To get even better results I could do more of the same experiment and overall get the class average. A known mass of the primary standard is dissolved in distilled water?? ?? and the volume of the solution is made up to a known volume. Use a pipette filler to suck up the liquid into the pipette Allow liquid to run slowly down to the graduation mark Run the liquid into a conical flask Touch the side of the flask with the tip of the pipette. ...read more.

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