Question

How would you make a 1.75M solution of sucrose using solid sucrose, a 2mL graduated pipet, and a 25mL volumetric flask?

How would you make a 0.500M solution of sucrose by diluting the solution in the previous question?

Answer 1

We have to make 1.75 M solution of Sucrose.

Molarity(M) = (moles of solute) / (Volume of solution in litres)

Here, we will make 25 ml of solution in the 25 ml volumetric flask.

Then, Volume of solution = 0.025 L.

moles of solute = 1.75*0.025 = 0.04375

then grams of Sucrose we need to prepare 1.75 M solution = 0.04375*342.3 = 14.976 gm. [molecular wt. = 342.3]

Now,

1. Add 14.976 gm of sucrose in the flask

2. Slowly, add water in the flask. In the volumetric flask their will be marking(indication) for 25 ml volume. So, add water in the flask and when the water level reaches near to marking, use 2 ml pipet so that the accuracy is quite high and you will get exact molarity solution.

Now, we have to dilute the solution, to prepare 0.5 M solution.

we have formula for dilution, M₁V₁=M₂V₂  -------1

where, M₁ and V₁ are the molarity and volume of solution before dilution,

M₂ and V₂ are the molarity and volume after dilution.

By equation 1.

M₁V₁=M₂V₂

=> 1.75*.025 = 0.5*V₂

=> V₂ = 0.0875 L = 87.5 ml

Water to be added = 87.5 - 25 =62.5 ml

Therefore, to make 0.5 M solution we have to add extra 62.5 ml of water in the beaker or bigger volumteric flask.