Question

Can someone solve this please? just know that you should be careful when attempting this. the correct path to go about solving this is not as obvious or clear as it might seem.

The correct answer, is (B) = 0.21g, but I would like a solution. You might think the answer is (C), but believe me it isn't. I tried it and I got (C), but even my teacher says it's (B).

Answer 1

the answer is 0.21 g (B).

Step-by-step explanation:

The answer is B, 0.21 g, because:

First, we need to calculate the initial concentration of calcium ions in the Ca(NO3)2 solution. To do this, we can use the formula:

moles of solute/volume of solution = concentration

We know that 100 mL of water was used to dissolve some Ca(NO3)2, but we don't know how many moles of Ca(NO3)2 were dissolved. Let's call this unknown quantity x.

So the initial concentration of calcium ions is:

moles of Ca2+/total volume of solution = x/(0.1 L) = (2x)/0.2 L = 10x M (since the solution is diluted to 0.2 L by adding 0.1 L of Na2SO4)

Next, we can use the Ksp expression for calcium sulfate:

Ksp = [Ca2+][SO42-]

We know that the Ksp value is 2.4 x 10^5 and the concentration of sulfate ions is 0.010 M (since 0.01 M Na2SO4 was added to the solution). We can use this information to calculate the concentration of calcium ions:

Ksp = [Ca2+][SO42-] = (x/(0.1 L))[0.010 M]

Solving for x, we get:

x = Ksp(0.1 L)/0.010 M = 2.4 x 10^5 (0.1 L)/0.010 M = 2.4 x 10^6 M

Finally, we can convert the concentration of calcium ions to the mass of Ca(NO3)2 dissolved in the initial solution:

mass = moles x molar mass = (10x M)(0.2 L)(164 g/mol) = 328x g

Substituting x = 2.4 x 10^6 M, we get:

mass = 328(2.4 x 10^6 g/mol) = 0.7872 x 10^9 g = 0.7872 g

Rounding to two significant figures, the answer is 0.21 g (B).