Question

7.How would the molar mass of the unknown acid be affected (higher, lower, or no change) if the follow-ing errors occurred? Briefly explain why in each case.

a.The pH meter was incorrectly calibrated to read lower than the actual pH.

b.During the titration, several drops of NaOH missed the reaction beaker and fell onto the bench top.

c.In Part B of the procedure the acid was dissolved in 75 mL of distilled water rather than the 50 mL called for in the procedure.

Answer 1

a) when we note down low value of pH than the actual pH value, in that case concentration of H+ would be more therefore no. Of moles would be more and molar mass will be less.

Concentration is equal to no. Of moles per litre of solution. And no. Of moles is equal to mass divided by molar mass.

So when no..of moles is high, molar mass is less.

b) M1V1 = M2V2

Molarity of NaOH (M1) is fixed, Volume of NaOH (V1) is more because some drops are wasted . Also volume of acid (V2) is fixed.

So when V1 is more, than molarity of acid will also be higher . Therefore again in this case no. Of moles is more and molar mass reduces.

c) In this case , acid is diluted therefore it's molarity or concentration is less which makes the no. Of moles to be less and due to which molar mass increases.