How many moles of Ca2+ ions are in 0.150 moles of calcium titanate, CaTiO3?

Question

Part 1-

How many moles of Ca²⁺ ions are in 0.150 moles of calcium titanate, CaTiO₃?

Part 2-

What is the mass of these Ca²⁺ ions?

Answer 1

Hello Kirsten,

For Part 1 you need to start with the moles of the compound and convert to moles of the ion by looking at how many Ca²⁺ ions there are in the CaTiO₃ compound. Since this compound breaks up into Ca²⁺ and TiO₃^2- the conversion is 1 mole Ca²⁺ = 1 mole CaTiO₃ . (If it were something like Ca₂C, then the ratio would be 2 moles Ca²⁺ = 1 mole Ca₂C and you want to make sure you take that 2 into account in your math).

Part 1-

How many moles of Ca²⁺ ions are in 0.150 moles of calcium titanate, CaTiO₃?

0.150 moles CaTiO₃ X (1 mole Ca²⁺ / 1 mole CaTiO₃) = 0.150 mole Ca²⁺

Part 2-

What is the mass of these Ca²⁺ ions?

Taking the moles of Ca²⁺ from part 1 and using the molar mass of Calcium from the periodic table (g/mole) you can convert from moles to grams. Weight of an ion and its neutral form are pretty much the same since the loss of 2 electrons is negligible.

0.150 mole Ca²⁺ X (40.078 g Ca²⁺/mole of Ca²⁺) = 6.0117 g --> 6.01 g Ca²⁺ (rounded to 3 significant figures since that is what the starting information was in)

Let me know if you need any further clarification.

Best,

Kristy

Answer 2

Kirsten

As you have 0.150 moles of the compound, and there is 1 Ca²⁺ ion per molecule, there must be 0.150 moles of Ca²⁺ ions.

The atomic mass of Ca is 40.078 so 0.150 moles of Ca atoms would have mass 0.150 x 40.078 = 6.0117 g

A Ca ²⁺ ion is a Ca atom with 2 electrons removed, so technically to answer the second question you need to take off the mass of 0.150 x 2 = 0.30 moles of electrons from 6.0117g.

One electron has mass 9.1 x 10^-28g so 0.30 moles has mass 0.30 x 6.02 x 10²³x 9.1 x 10 -²⁸ = 0.0001 g , giving a final answer of 6.0116 g

MIKE