1. Suppose you have a sample of sodium weighing 11.43 g. How many atoms of sodiu

Question

1. Suppose you have a sample of sodium weighing 11.43 g. How many atoms of sodium are present in the sample?
_____atoms

2. What mass of potassium would you need to have the same number of potassium atoms as there are sodium atoms in the sample of sodium?
_____g

3. What mass of cobalt contains the same number of atoms as 53.0 g fluorine?

_____ g

4. Use the average atomic masses given inside the front cover of this book to calculate the number of moles of the element present in each of the following samples.

(a) 5.48 g of thallium_____ mol

(b) 74.3 g of scandium_____mol

(c) 123 mg of aluminum_____mol

(d) 7.58

Explanation / Answer

1) The number of atoms of Na = (11.43 g/23 g/mol)(6.022*1023 Na atoms) = 3.0*1023 Na atoms

2) Mass of potassium (K) = (3.0*1023 Na atoms*1 mol / 6.022*1023 atoms)(39.10 g/mol) = 19.47 g

3) Mass of Cobalt, Co = (53.0 g F / 19.0 g/mol) (58.93 g Co / 1 mol Co) = 164.38 g

4) a) Mols of Thalium, Tl = (5.48 g / 204.38 g/mol) = 0.0268 mol

b) Mols of Scandium, Sc = (74.3 g/44.96 g/mol) = 1.652 mol

c) Mols of aluminnum, Al = (0.123 g/27 g/mol) = 4.55*10-3 mol

d) Mols of gold = (7.58*10-6 g / 196.97 g/mol) = 3.848*10-8 mol

e) mols of cobalt, Co = (260 g / 58.93 g/mol) = 4.412 mol

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