Answer to Question #307738 in Physical Chemistry for Mona

Question

A Laboratory assistant prepares 5 litres of 0.1N hydrochloric acid stock solution using commercial HCl available in laboratory which has percentage purity of 35% (w/w) and specific gravity of 1.18 g/ml. Then he fills five 100ml standard flasks with 50.0ml of 0.1N HCl solution and dilutes it with distilled water upto the mark. Then he takes 10ml of diluted HCl solution from each flask into a conical flask, mixes it and adds 50ml of 0.025M Sodium hydroxide solution to it. Finally, he adds few drops of phenolphthalein to the resulting solution in the conical flask.

What was the concentration of HCl solution prepared in 100ml standard flasks?

What do you think will be the colour of the resulting solution after addition of indicator?

Calculate the pH of the resulting solution.

Answer 1

First of all check the specific gravity(sg) on HCL reagent bottle and percentage of concentration

Use the formula for stock calculation

N=sg*%*1000/(equivalent wts*100)

By this to find out stock normality of HCl solution

Now use

M1V1(stock)=M2V2(required) means

Required means 0.1N in 100mL

M2=0.1 and V2=100

M1= find from above formula i.e N=sg*%*1000/(equivalent wts*100)

Now you find V1 from M1V1=M2V2

When universal indicator is added to a solution, the color change can indicate the approximate pH of the solution. Acids cause universal indicator solution to change from green toward red. Bases cause universal indicator to change from green toward purple.

the components of a two-acid solution provide 0.025 and 0.015 mol of hydrogen ions (H+), respectively, and the mixed solution has a volume of 200 ml, the concentration will be 0.040 mol divided by 200 ml – or 0.0002 mol of H+. The -log of this concentration, and the pH, would then be 3.699