Question

Which of the following solutions have the same concentration?
A. 20g of NaOH in 200 mL of solution
B. 0.5 mole of KCl in 200 mL of solution
C. 40g of NaOH in 100 mL of solution
D. 20g of KOH in 200 mL of solution

Answer 1

Hint: Molarity of the solution is defined as the amount of number of moles which have been dissolved in 1 litre of the solution. So we represent the concentration in terms of molarity with the symbol of M. The molarity of the solution changes with the change in physical properties such as pressure and temperature.

Complete step by step answer:
Now to calculate the concentration of the substance we will use the formula of molarity. The formula is the following:
Molarity = $$\dfrac{{{ {mass \;of \;solute \times 1000}}}}{{{ {molar\; mass \;of \;solute \times volume \;of \;solution}}}}$$
Now for option (a)the mass of solute is 20g, the molar mass of NaOH will be = 23+16+1 = 40$${ {gmo}}{{ {l}}^{{ { - 1}}}}$$and volume of solution is 200 mL. Now substituting the value in formula we get,
Molarity = $$\dfrac{{20 \times 1000}}{{40 \times 200}}$$ = 2.5M
Now for option (b) the moles of the solute is given which is 0.5 moles, the volume of solution is 200 mL. The formula which we will be using here is :
Molarity = $$$$
Molarity = $$\dfrac{{{ {0}}{ {.5 \times 1000}}}}{{200}}$$ = 2.5M
Now for option (c) the value for mass of solute is 40g and the molar mass of NaOH is 40g and volume of solution is 100 mL. Now substituting the value:
Molarity = $$\dfrac{{{ {40 \times 1000}}}}{{40 \times 100}}$$ = 10M
Now for option (d) the value for mass of solute is 20g and the molar mass for
KOH = 39+16+1 = 56$${ = {gmo}}{{ {l}}^{{ { - 1}}}}$$ and volume of solution is 200 mL.
Now substituting the values in formula we get,
Molarity = $$\dfrac{{{ {20 \times 1000}}}}{{20 \times 200}}$$ = 5M

So, the correct answer is Option A,B.

Note: The one molar of the substance means the molarity of solution in which the 1 g of the solute has been dissolved in one litre of the solution. We take the complete volume of the solution because the solute as well as solvent is used to blend the solution. The molarity is the ratio of moles of solute to the volume of solution.