Question on chemistry mols of Iodide?

Question

If you have a .20M solution of potassium iodide, and use 20.0 ml, how do you find the mols of Iodide ions? Please show work, thank you.

Answer 1

Molarity x liters gives u moles. think about it, moles/L x Liters. Liters cancel.

.20M x 0.020L=0.004moles of potassium iodide, which is KI.

since there is 1 mol of iodide (I-) in KI the answer is still 0.004 mol.

Note: if it weren't KI, but it was something like CaI2, then u would have to multiply by 2.

Answer 2

Let potassium iodide solution be called S.

20.0mLS x 0.20molKI/1000mLS = 0.004molKI = 0.004mol I-

The 20.0mL solution is given. The first factor comes from the molarity of KI solution. The mL S cancel, leaving moles KI, which equals mols I-.