Question

you need to make 400 ml of a 50mM solution of sucrose in 3% KCI in water. you have water, you have sucrose, and you have kci. the molecular weight of sucrose is 342. the molecular weight of kci is 74.5. how do you make this solution? how many grams of sucrose will you need? how many grams of kci will you need?

Answer 1

given

final volume of solution = 400ml

molarity of solution = 50mM

% of KCl water = 3%

MW of sucrose = 342

MW of KCl= 74.5

first we calculate KCl require for to make 3% KCl water

we have to make 3% KCl water so that

3/100 x 400= 1200/100= 12

to make 3% KCl water we have to mix 12 gram of KCl in 400 ml of water.

we know that 1M solution means gram molecular weight of solute in 1 liter of solvent.

so that

to make 1M = 1000mM sucrose solution we have to dissolve 342 gram of sucrose in 1 liter of water

i.e 1000mM = 342 gram sucrose

if

1000mM= 342, then

50mM= x gram

x= 342 X 50 = 17100/1000 = 17.1gram in 1000ml

but we have to make only 400 ml

so that

if

17.1 gram =1000ml then

x gram = 400ml

x = 400 *17.1/1000 = 6.84gram

to make 50mM of 400ml sucrose solution we have to dissolve 6.84 gram of sucrose in 400ml of water

finally to make 3% KCl water with 50mM sucrose you have to dissolve 12gram of KCl and 6.84 gram of sucrose in 400 ml of water