Question

if i add 25 ml of water to 135 ml of a 0.25 M NaOH solution what will the molarity of the diluted solution be​

Answer 1

Answeri think 0.21 M

Step-by-step explanation:

Answer 2

0.21 M. (2 sig. fig.)

Step-by-step explanation:

The molarity of a solution is the number of moles of the solute in each liter of the solution. The unit for molarity is M. One M equals to one mole per liter.

How many moles of NaOH in the original solution?

`n = c \cdot V`,

where

• 
  `n` is the number of moles of the solute in the solution.
• 
  `c` is the concentration of the solution.
  `c = 0.25 \;\text{M} = 0.25\;\text{mol}\cdot\textbf{L}^(-1)` for the initial solution.
• 
  `V` is the volume of the solution. For the initial solution,
  `V = 135\;\textbf{mL} = 0.135\;\textbf{L}` for the initial solution.

`n = c\cdot V = 0.25\;\text{mol}\cdot\textbf{L}^(-1) * 0.135\;\textbf{L} = 0.03375\;\text{mol}`.

What's the concentration of the diluted solution?

`\displaystyle c = (n)/(V)`.

• 
  `n` is the number of solute in the solution. Diluting the solution does not influence the value of
  `n`.
  `n = 0.03375\;\text{mol}` for the diluted solution.
• Volume of the diluted solution:
  `25\;\text{mL} + 135\;\text{mL}  = 160\;\textbf{mL} = 0.160\;\textbf{L}`.

Concentration of the diluted solution:

`\displaystyle c = (n)/(V) = \frac{0.03375\;\text{mol}}{0.160\;\textbf{L}} = 0.021\;\text{mol}\cdot\textbf{L}^(-1) = 0.021\;\text{M}`.

The least significant number in the question comes with 2 sig. fig. Keep more sig. fig. than that in calculations but round the final result to 2 sig. fig. Hence the result: 0.021 M.