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# Determine the unknown concentration of three acid solutions using a standard known concentration of alkali.

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Introduction

Aim The aim of this experiment is to determine the unknown concentration of three acid solutions using a standard known concentration of alkali (which is also known as 'base'). The three acids that will be utilised in this practical are hydrochloric acid, ethanoic acid and sulphuric acid. The concentration of the acid will be determined by titrating the acid against the base. In this scenario sodium hydroxide will be titrated against the three acids named above. Theory In water, sodium hydroxide is a strong base. It separates into sodium and hydroxide ions. The most common strong bases are the water-soluble hydroxides that belong to sodium, potassium & lithium; all three can be referred to as ionic solids. A solution containing 0.5mol of dissolved NaOH per litre of solution will also contain 0.5mol dm-3 of OH- ions. This is due to the ratio being on a 1:1 basis. Please refer to the example below. NaOH Na+ + OH- When bases react with acids the reaction that takes place is known as neutralisation. In a 1:1 ratio of acid if there are 0.1 mols of hydrogen ions (H+) ...read more.

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Conclusion

1. HCl +NaOH NaCl + H2O (ratio = 1:1) 2. 0.1 x 24.1 = 2.41 x 10-3 x 1000 = 0.0964 mol dm-3 1000 25 3. CH3COOH + NaOH CH3COONa + H2O (ratio = 1:1) 4. Mol of NaOH = 0.1 x 25.05 = 2.50 x 10-3 = 0.1002 mol dm-3 1000 2 5. 6. H2SO4 + 2NaOH Na2SO4 + 2H2O (0.1 x 55.20 = 5.52 x 10-3) 7. Ratio = 1:2 � � � 2.76 x 10-3 x 100 = 0.1104 mol dm-3 25 Please note that as the ratio was 1:2, 5.52 had to be divided by 2. 8. 9. Contamination was one error source that had occurred; this was due to some people sticking the pipette directly into the acids, which meant that there could have been a chance that the acid had been contaminated. In the future this can be avoided by the proper use of a conical flask to transfer to the pipette. 10. Weak acid - substances capable of donating hydrogen but do not completely ionize in solution. Strong acid - an acid that completely dissociates to produce an H+ ion and the conjugate base 11. 12. ...read more.

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