An Investigation of Titration

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Tom Burgess Yr 11 set 1                Chemistry Coursework

Introduction

I am going to do an investigation on how much acid is needed to neutralise a certain amount of alkali. The acid that I will use is hydrochloric acid and the alkali I will use is sodium hydroxide.

Hydrochloric Acid

Hydrochloric acid (HCl) contains hydrogen and chlorine and is ionically bonded.

Hydrochloric acid looks like this:

Sodium Hydroxide

Sodium Hydroxide (NaOH) is made up from Sodium, Hydrogen and oxygen. NaOH is ionically bonded and it looks like this:

Acids, Alkalis and Neutralisation        

An acid is a proton donor and an alkali is a proton receiver. An Acid will have a pH less than 7 and an alkali will have a pH of more than 7. An acid with a pH of 1 is the strongest as ALL of the Hydrogen ions are ionised. The strongest alkali, with a pH of 14, is when ALL the hydroxide ions are ionised.  

Neutralisation is when an acid and an alkali of equal strengths are mixed, the pH will be 7 and salt and water is produced. In more detail it is when ionised hydroxide and hydrogen meet and share electrons.  

When a substance is diluted the concentration is weakened. The molarity changes when the water is added.

The indicator will change colour when neutralisation occurs, also the temperature will stop rising.

Choosing an Indicator

I will find the best indicators to use in my experiment, the three indicators that I will compare are:

Phenol Phtalein

Methyl Orange

Universal Indicator

I will find which indicator is more beneficial for my experiment by filling a test tube with about 1/3 of Sodium Hydroxide and then adding a small amount of an indicator in, the first indicator I used was the Universal Indicator. As I added the hydrochloric acid to the sodium hydroxide it became neutralised and the colours kept changing as the substance changed from acid to alkali, it was very difficult to establish when you have reached neutralization as the colour changes to easily.

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When I added the Methyl Orange to another sodium hydroxide, it went red for the acid but wasn’t clear when neutralization had occurred.

When I used Phenol Phtalein the substance turned purple when an alkali and went clear when neutralization took place. It was very obvious when the substance was neutralised to the single drop. Therefore the indicator that I will use to judge when the substance is neutralised is the Phenol Phtalein

Measurement of Liquids

My most accurate method to measure the acid is by using a syringe pipette to create negative pressure and absorbing ...

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Here's what a star student thought of this essay

The author uses scientific vocabulary to good effect, but makes some grammar errors, and could make their writing more sophisticated. I think had they expressed themselves better their coursework could have been improved.

The author could have expanded their experiment to cover multiply acids and alkalis, and if I had conducted this experiment and had had the time, I would have done so. It is excellent that the author mentioned the bonding in the molecules, but needed to check their facts before submitting their coursework. It was good that they put in the equation “acid + alkali --> salt + water” and putting in “HCl + NaOH --> NaCl + H2O” was also useful. Their explanation of the pH scale was slightly inaccurate, but that may be simply because they are doing GCSE chemistry. Their neutralisation shows reasonable results, but they did not give the concentrations of the acid or alkali, which they should have done. Ideally the author would have considered some of the major problems before doing their experiment (such as spilling things) and tried to eliminate them before conducting it. They could have improved their experiment by doing more neutralisations, and then creating a graph with error bars. They could also have used different amounts of acid and alkali to check the trend continued. The same applies to the investigation into temperature.

The essay is of a reasonable standard, with few factual errors, but the standard of English could be improved, there is no graph, and some over-generalisations have been made. Hydrochloric acid is covalently bonded, not ironically bonded. The author has implied that all acid-alkali neutralisations have a 1:1 acid:alkali ratio when this is not always the case. The author does answer the question set “How much acid neutralises a certain amount of alkali?”, but probably should have made the question more specific because their experiment is only on a single acid and a single alkali.