Question

A 17.0-g sample of hf is dissolved in water to give 2.0 x 10 2 ml of solution. the concentration of the solution is:

Answer 1

 The  concentration  of the solution  is   4.25 M

 Explanation

molarity=moles/volume in liters

moles  = mass/molar mass
molar mass  of HF = 19 + 1 =  20 g/mol
moles is therefore = 17.0 g/ 20 g/mol  = 0.85  moles

volume in  liters = 2  x10^2ml/1000 = 0.2  liters

therefore  molarity =  0.85/0.2 = 4.25  M

Answer 2

Answer:

The concentration of the HF solution: M = 4.25 M

Explanation:

Molarity, denoted by M, is the molar concentration of a given solution. It is the ratio of number of moles of solute and the total volume of the solution in L.

Molarity of a solution is given by,

$M = \frac{Number\: of\: moles\: of \: solute\: (n)}{Total\: volume\: of\: the\: solution\: (V)(in\: L)}$

and,  $n = \frac{Given\: mass\: of\: solute\: (w)}{Molar\: mass\: of\: solute\: (m)}$

Given: Total volume of solution: V = 2 × 10² mL = 2 × 10² × 10⁻³ L = 0.2 L    (∵ 1 mL = 10⁻³ L)

Given mass of solute (HF): w = 17 g, Molar mass of solute (HF): m = 20 g/mol

Molarity of HF solution: M = ?

So the number of moles of solute (HF):

$n = \frac{w}{m} = \frac{17\: g}{20\: g/mol} = 0.85\: mol$

Therefore, the Molarity of the HF solution:

$M = \frac{n}{V(in\: L)} = \frac{0.85\: mol}{0.2\: L} = 4.25\: mol/L\: or\: 4.25\: M$

Therefore, the concentration of the HF solution: M = 4.25 M