Question

Compound A is a water-soluble solid at room temperature with a molecular weight of 138.12 amu. Describe one (or more) experiment(s) that you would perform in lab to determine if Compound A is a strong acid, weak acid, strong base, weak base, or none of these in water. State what you would do, what you would measure, and how you would decide the nature of Compound A in water?

Answer 1

There are two ways to decide the nature of Compound . Both these ways are based on one common principle,pH.pH is a numerical scale which is used to identify the nature of a given compound in its solution with water, The pH scale ranges from 0 to 14. If the pH of the solution of a compound with water is less than 7, then the compound is acidic whereas if the pH is more than 7 then the compound is basic. On the other hand, if the pH of solution is 7 then the compound is neutral.

In this case, the compound A when mixed with water will give a homogeneous solution. In the first method, this soluton is then tested on pH paper. pH paper is a small strip which when dipped in the solution or a drop of solution is placed on the pH strip, the strip will change its color based on the pH of the solution. This color can be then matched with the color code mentioned on the packing of the pH strip and the pH value associated with a color on the package of the pH strip,the solution's pH can be estimated. If the color of pH strip is green, then the compound A is neutral. If the color of the strip becomes red (pH =2) or dark red(pH <=1), then compound A is strong acid and if the color of the strip becomes dark blue (pH=13) or a dark purple(pH=14), then compound A is strong base. If the color of pH strip is orangish to light greenish, then its pH lies between 2 to 7 indicating compound A is weak acid. If the color of the pH strip is between dark green to blue, then the pH lies between 7 to 12 indicating compound A to be a weak base.

Another method is to use the pH meter. This pH meter has a glass probe which measures the solution's ion conncentration when inserted in the solution. When the probe is placed in the solution it will yield the exact pH numerical value of the solution of compound A. As in previous case, if the numerical value of pH from pH meter gives value less than or equal to 2, then the compund A is strong acid. If pH lies between 2 to 7 then it is weak acid.Similarly, if pH lies between 7 and 13 then the compound A is weak base whereas if pH is greater or equal to 13 then compound A is strong base.