Question

The mass of solute per 100 mL of solution is abbreviated as (m/v). Mass is not technically the same thing as weight, but the abbreviation (w/v) is also common. How many grams of sucrose are needed to make 795 mL of a 40.0% (w/v) sucrose solution? sucrose MISS

Answer 1

40% w/v sucrose solution means that there are 40 g of sucrose in 100 mL solution.

Or we can say, 100 mL contains 40 g sucrose

$\Rightarrow$ 1 mL solution contains (40/100) g sucrose

$\Rightarrow$ 795 mL solution contains (40/100) X 795 g sucrose = 318 g sucrose

Molarity is defined as number of moles of solute present per liter of solution.

So, M = moles of solute / L of solution

As explained earlier % (m/v) equals the mass of solute per 100 mL of solution.

So, % (m/v) = (grams of solute / mL of solution) X 100

Molarity = no of moles of solute / vol of solution (in L)

So, Molarity of NaOH solution = 0.2 mol / 1.85 L = 0.37 M

To calculate the molarity of NaCl solution we need to calculate moles of NaCl present in 23.5 g of NaCl

no of moles = given mass / molar mass =  23.5 g / 58.44 g mol^-1 (molar mass of NaCl = 58.44 g mol^-1 )

moles of NaCl = 0.402 mol

Volume of solution = 631 mL = 0.631 L

So, Molarity of NaCl solution = 0.402 mol / 0.631 L = 0.637 M

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