Question

If an ion of Na+ has a mass of 23, and Cl- has a mass of 35, how many grams of NaCl are added to 100ml of water to make a 3M solution?

a)580b) 5.8 c)17.4 d)35

Answer 1

Answer : The correct option is, (C) 17.4 grams.

Explanation : Given,

Mass of $Na^+$ = 23 g

Mass of $Cl^-$ = 35 g

Volume of solution = 100 mL

Molarity = 3 M = 3mol/L

Molar mass of $NaCl$ = 23 + 35 = 58 g/mole

Molarity : It is defined as the number of moles of solute present in one liter of volume of solution.

Formula used :

$\text{Molarity}=\frac{\text{Mass of }NaCl\times 1000}{\text{Molar mass of }NaCl\times \text{Volume of solution (in mL)}}$

Now put all the given values in this formula, we get:

$3mol/L=\frac{\text{Mass of }NaCl\times 1000}{58g/mole\times 100mL}$

$\text{Mass of }NaCl=17.4g$

Therefore, the mass of NaCl added are, 17.4 grams.