Answer:
3.998 M
or, if considering significant figures,
4 M
Step-by-step explanation:
Molarity is a unit of concentration used to express the concentration of a solution in terms of moles of solute per liter of solution. To calculate the molarity of a solution, we need to know the number of moles of solute present in the solution and the volume of the solution in liters.
We can use the formula:
Molarity = moles of solute / liters of solution
We are given the mass of the solute: 40 grams of HF. The molar mass of HF is 20.01 g/mol. By dividing the mass of HF by the molar mass of HF, we can obtain the number of moles of HF: (40 grams HF) / (20.01 grams HF/moles HF) = 1.999 moles HF.
The volume of the solution is given as 500 mL, which is equivalent to 0.5 L.
Now we can use the formula to calculate the molarity:
Molarity = moles of solute / liters of solution = 1.999 moles HF / 0.5 L = 3.998 M HF.
Therefore, the molarity of the solution when 40 grams of HF are added to water to make a 500-mL solution is 3.998 M.
Note that all numerical quantities in the question are given to one significant figure. So, if you must also consider significant figures, the molarity of the solution would be 4 M. Since it is not entirely clear whether you are to disregard significant figures for this question, I will provide you with both representations.