Question

please answer 45

Solutions 41. Calculate the quantity of grams found in 250 ml of a 15% w/ solution of Non 42. Calculate the quantity of grams found in 475 mL of a 30% w/ solution of KCL 43. How many ml of a 90% ethyl alcohol solution are needed to prepare 150 mL of a 10 eur alcohol solution? 44. Determine the quantity of stock 75% EtOH required to prepare 300 mL of a 25% EtOH solution. 45. Determine the concentration of a solution if 300 mL of a 20% buffer solution was diluted to a final volume of 1000 mL.

Answer 1

41) Given :- 15% w/v solution of NaOH

Calculations :-

100 ml solution contains 15g soute.

1 ml solution contains 15/100 = 0.15g g solute

250 ml solution contains 0.15×250 = 37.5g solute

Hence the mass of solute present in 250 ml of 15% solution is 37.5 gram.

42) Given :- 30% w/v solution of KCl

Calculations :-

100 ml solution contains 30g solute.

1 ml solution contains 30/100 = 0.30g solute

475 ml solution contains 0.30×475 = 142.5g solute

Hence the mass of solute present in 475 ml of 30% solution is 142.5 gram.

43) given :-

90% ethyl alcohol solution 1st

To prepare :- 150 ml of 10% ethyl alcohol solution 2nd

Calculations :-

a) 1st solution:-

100 ml solution should have 10g ethyl alcohol

1 ml solution should have 10/100 = 0.1g ethyl alcohol

150 ml should have 0.1×150 = 15g ethyl alcohol

b) 2nd solution:-

90g ethyl alcohol present in 100 ml solution

1g ethyl alcohol present in 100/90 = 1.11 ml solution

15g ethyl alcohol present in 1.11×15 = 16.66 ml solution

Hense volume of 90% ethyl alcohol required to prepare 150 ml of 10% ethyl alcohol solution is 16.6 ml

44) Given :-

75% ethyl alcohol solution 1st

To prepare :- 300 ml of 25% ethyl alcohol solution 2nd

Calculations :-

a) 1st solution:-

100 ml solution should have 25g ethyl alcohol

1 ml solution should have 25/100 = 0.25g ethyl alcohol

300 ml should have 0.25×300 = 75g ethyl alcohol

b) 2nd solution:-

75g ethyl alcohol present in 100 ml solution

Sense the volume of 75% ethyl alcohol solution required to prepare 300 ml of 25% ethyl alcohol solution is 100 ml