Calculate the number of moles...?

Question

Calculate the number of moles in the following:

1. 4.99 kg of titanium

2. 6.53 mg of calcium

3. 1.01 g of ruthenium

4. 1.14 pg of technetium

or could someone just explain to me how to find it myself, or both? Thanks.

Answer 1

first calculate mass of given atom of compound

number of moles= amount in grams / molecular or atomic mass  

Answer 2

To calculate the number of moles, you divide the actual amount by the relative formula mass.

Answer 3

Atomic mass titanium = 47.88g  4990g Ti = 4990/47.88 = 104.22moles

Atomic mass calcium = 40.078g  0.00653/40.078 = 1.63*10^-4 moles

Atomic mass ruthenium = 101.07g  1.01/101.07= 9.99*10^-3 moles

Atomic mass technetium = 98.906 Let us take a stop here for this element. Technetium is an unstable element and I have used the most stable known isotope. 1.14pg is  1.14*10^-12 grams so you will have:

(1.14*10^-12) / 98.906 = 1.15*10^-14 moles.

This is an incredibly small quantity of technetium, but it is still 6.94*10^9 atoms.