1 of 5 Bases, Acids and Antacids INTRODUCTION The terms acid and base are used q

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1 of 5 Bases, Acids and Antacids INTRODUCTION The terms acid and base are used quite looscly in chemistry and may have slightly different meanings under different circumstances. We will generally be using these terms to refer to chemical substances that dissolve in water. Kcep in mind that an acid is a substance that increases the amount of H ion in water and a base is a substance that increases the amount of OH ion in water. It is important to rcalize that as the amount of H ion increases in water, the amount of Oll ion decreases by a proportionate amount. T concentration in pure water or dilute aqueous solutions will be constant (note -the square brackets [ ] around a chemical species represents the concentration of that species): The product of their molar The relative acidity or basicity of aqueous solutions is measured as pH (notice that the symbol used is lower case p followed by upper case H), which is defined as: pH--log [H'] What this means is that for every change in the concentration of H by a factor of 10, the pH will change by a factor of 1 . When [H] is 10'2 M, the pH is 2 and when [H] is 10,5 M, the pH is 5. When the pH is 12, this means H is 10 M, which is a very small amount ( trillionth molar or 1/1,000,000,000,000). In contrast, the [OH] will be relatively large at pH 12, 102 M We encounter acids and bases frequently in our daily routines, although we don't always think about the acid or base properties of the myriad substances we come in contact with each day. We have discussed acid rain in the course and saw how it fits into the larger picture of our environment. Many of the foods we eat are acidic or alkaline (alkaline is another word for basic that can be used to avoid confusion with the word basic when it is used to mean "fundamental"). Acidic foods tend to taste sour (e.g., many fruits, especially citrus and tomatoes). Many foods that taste bitter are alkaline. But because we can perccive so many different tastes, the taste test isn't always a good indicator of whether substances are acids or bases. In this laboratory exercise you will measure the acidity of vinegar and the relative

Explanation / Answer

1) Phenolphthalein is used in titration of vinegar with aqueous NaOH solution. As vinegar and NaOH both are colourless we can not detect the end point of the titration. Phenolphthalein is colourless in acidic solution, and pale pink in alkaline region ( pH=8) .So when the acid is completely neutralized by the base the solution turns pale pink .Excess addition of base intensify the color.

2) An antacid tablet is dissolved in known amount of acid.Some of the acid will be neutralized by the acid and the excess acid is titrated by base. Here Congo red dye indicator is used to detect the end point. It shows blue color in acidic region (pH=3) and red colour in alkaline region (pH=5.2). As the is initially acidic the solution shows blue colour. When the acid will be completely neutralized by the base ,the solution will turn red in color. Hence with the help of this indicator we can detect the end point .

3) From the above experiment we can see that the 1st antacid tablet can neutralise 4.2mEq of acid which is more than the other two .So we can say that 1st tablet can neutralise more acid ,so it would give more relief from Excess stomach acid.

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