Review Question [ENDORSED]

[204929947]

I am not sure how to solve the question from the review test on our first quiz, can someone please help me
Question: Hard water is water that has high mineral content (mainly Calcium and Magnesium). A concentration above 5.30 x 10−3 M is considered to be very hard water. Assuming that there are no magnesium ions present, is a 0.400 L solution of 0.120 g CaCO3 and 0.155g CaSO4 very hard water?

[april_bussey_1C]

So in order to solve this problem, you have to first think about what it is that the question is asking you to find. The question is asking you to compare the molarity that indicates hard water (5.30 x 10 -3) with the given information. This means that you need to figure out the molarity with the given information. We know that molarity is the moles/liters of solution so let's check what we have with the given information...... we have the liters (.400) but they only give us the mass of the solution, In order to correctly firgure out the Molarity to compare with the number given (5.30 x 10 -3) we have to convert both compounds to moles, add them together, and then plug that number of moles into the molarity formula to get the overall molarity. Once we get the molarity with the given information, compare to the molarity of very hard water. My answer is yes, it is very hard water because the molarity was 5.75 x 10 -3. Hope this helps :) GOOD LUCK!

[Hope_Pham_1G]

The molarity formula is moles of solute (n) divided by liters of solution (V). The units of molarity is mol/L (M). M can be substituted with c, which indicates a broader calculation of concentration.

[905085650]

I keep getting 5.75 x 10^-4 instead of 10^-3...

What am I doing wrong?