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A Comparison of Strong and Weak Acids and Bases

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Introduction

A Comparison of Strong and Weak Acids and Bases DATA COLLECTION Qualitative Data Table 1.1: The lists of the solutions being used in this experiment and classifying if it is a strong acid or base or a weak acid or base. Solutions Classifications H2SO4(aq) Strong acid HCl(aq) Strong acid HNO3(aq) Strong acid CH3COOH(aq) Weak acid NaOH(aq) Strong base NH3(aq) Weak base H2O(l) Neutral Table 1.2: The appearance of the marble chip used and the magnesium ribbon. Object Appearances Marble chip Coarse, hard , and leaves white powder when held. Magnesium ribbon Shiny silver colour and ductile, i.e. can be bent without breaking it. Note: The chemical formula for marble chip is CaCO3(s) and for magnesium ribbon is Mg(s). Table 1.3: The observations upon reacting different solutions and concentrations of acid with the marble chips, CaCO3(s). Before marble chip is placed in acid solutions. During the reaction between marble chips and acid solutions After reaction has stopped All solutions were colourless As soon as marble chip were placed in the acid solution, bubbles of gas were seen*. Some of the reaction finishes faster than the others. The order in which in this reaction occurs can be seen in Table 1.4. For H2SO4(aq), reaction did occur slowly in the beginning. This reaction however stops. Table 1.4: The order in which the speed of reaction occurs between the acids and the CaCO3(aq). ...read more.

Middle

Thus a "check is done": 1.00M of NH3(aq) Chemical Equation: Necessary formulas: From the Data Booklet, pKb of NH3(aq) is 4.75. Thus, Therefore, Actually, the formula for dissociation constant for a weak base is: However, since the [OH-] is very, very, very small, the [OH-] in ([NH3 (aq)] - [OH-(aq)] is ignored. It is suggested that if the [OH-] is 10% or less of the concentration of the base, then it does not cause any major differences. Thus a "check is done": Table 2.1: The theoretical pH values for CH3COOH(aq) and NH3(aq) with its respective concentrations. Solutions Used Concentration of Solution / mol dm-3 Theoretical pH values CH3COOH(aq) 1.00 2.38 NH3(aq) 1.00 11.62 * No uncertainty was allocated for the theoretical values as the values used for calculations were taken as exact values prepared by the lab technician. The pH calculations for weak acids and bases differ to that of strong. This is because in strong acid and bases, it fully dissociates but in weak acids and bases, it only partially dissociates. This also explains why although they have the same concentrations, their pH values are not the same. For example, 1.00M of HCl(aq) and 1.00M of CH3COOH(aq) has the same concentration, however, their pH differs, being pH 0 for HCl(aq) and pH 2.38 for CH3COOH(aq). Table 2.11: Comparison of theoretical pH value and experimental pH value. ...read more.

Conclusion

Therefore, it can be concluded that the conductivity of acids or bases comes in the order below: Strong acid > Strong base > Weak acid > Weak base As the reacgion of acids with CaCO3(s), it can be seen that the reaction is faster with higher concentration of the acid. This can be seen when 1.00M , 0.10M and 0.01M of HCl(aq) was reacted with CaCO3(s) and 1.00M reacted the fastest whilst 0.01M was the slowest. In addition, it is seen that although H2SO4(aq) was a strong acid, it reacted the slowest among the 1.00M of acids(HCl(aq) and HNO3(aq)) including the weak acid CH3COOH(aq) As for the reaction of H2SO4(aq), HCl(aq) , HNO3(aq), and CH3COOH(aq) with magnesium ribbon, it is again seen that as concentration increases, so will the speed of reaction. However, for this reaction, H2SO4(aq) was the most reactive, as it produces MgSO4(aq) + H2(g), thus nothing is hindering the reaction from occuring. It is also seen that the weak acid, CH3COOH(aq) has the slowest reaction amongst the 1.00M acids (H2SO4(aq), HCl(aq) and HNO3(aq)). The colour change that occurred when CuO(s) was heated in warm acid is related to the states of the electrons in the metal. Atoms absorb and emit specific energies of photon corresponding to the metal's different state of acceptable states for electrons. Therefore, as the mixture was heated, the states available changes and this cause the colour of the solution to change as frequency of transmitted light is different. ?? ?? ?? ?? ...read more.

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