Question

how many grams of nacl (molar mass = 58 g/mol) are needed to prepare 100. ml of a 0.25 m nacl solution?
a 1500 g
b 15 g
c 5.8 g
d 1.5 g

Explanation:

Step1: Convert volume to liters

$V = 100\ mL=100\times10^{- 3}\ L = 0.1\ L$

Step2: Calculate moles of NaCl

Use the formula $n = M\times V$, where $M = 0.25\ mol/L$ and $V = 0.1\ L$. So $n=0.25\ mol/L\times0.1\ L = 0.025\ mol$

Step3: Calculate mass of NaCl

Use the formula $m=n\times M_m$, where $n = 0.025\ mol$ and $M_m = 58\ g/mol$. So $m = 0.025\ mol\times58\ g/mol=1.45\ g\approx1.5\ g$

Answer:

D. 1.5 g