1. The atomic mass unit is presently based on assigning a mass of exactly 12 amu

Question

1.The atomic mass unit is presently based on assigning a mass of exactly 12 amu to:

(a) an atom of carbon isotope 13C      (b) an atom of carbon isotope 12C     (c) all carbon atoms

(d) the average atomic mass of carbon

Which of the following samples contain the greatest number of oxygen atoms?

(a) 1mol H2O (b) 3 x 1023 molecules O3    (c) 1mol CO2   (d) 1mol CO

Approximately, how many oxygen molecules are in a 16.00 g sample of oxygen?

(a) 1 x 1023    (b) 2 x 1023    (c) 3 x 1023    (d) 6 x 1023     (e) 8 x 1023   

The number of moles of nitric acid (HNO3) present in 126.04 g of nitric acid is:

   (a) 1    (b) 2    (c) 0.5    (d) 1.5

Which one of the following is a correct expression for molarity?

   (a) mol solute/L solvent     (b) mol solute/L solution       (c) mol solvent/L solution

   (d) mol solution/L solvent

How many grams of potassium chloride are there in 100.0 ml of 1.50 M KCl ?

   (a) 11.2 g (b)112 g ( c) 1.12 g (d) None of these

Which statement is not true?

   (a) 1 mole of Na2CO3 contains same number of Na+ cations as CO32- anions

   (b) 1 mole of Na2CO3 contains twice as many Na+ cations as CO32- anions

   (c) 1 mole of Na2CO3 contains Na+ cations and CO32- anions in the ratio 2:1

   (d) 1 mole of Na2CO3 contains twice the Avogadro number of Na+ cations

Which one of the following molecular formulas is not an empirical formula?

   (a) CHO     (b) C2H2O3     (c) C6H9O3       (d) C12H14O3      (e) C14H12O3

Please help!!!

Explanation / Answer

1.The atomic mass unit is presently based on assigning a mass of exactly 12 amu to:

Ans: (b) an atom of carbon isotope 12C

2. Which of the following samples contain the greatest number of oxygen atoms?

Ans: (a) 1mol H2O (Oxygen atoms present is 5.35 x 1023 atoms)

3. Approximately, how many oxygen molecules are in a 16.00 g sample of oxygen?

Ans: (c) 3 x 1023

4. The number of moles of nitric acid (HNO3) present in 126.04 g of nitric acid is:

Ans: (b) 2 (no. of moles = 126.04/63.02 = 2)

5. Which one of the following is a correct expression for molarity?

Ans: (a) mol solute/L solvent

6. How many grams of potassium chloride are there in 100.0 ml of 1.50 M KCl

Ans: (a) 11.2 g ( 0.15 x 74 = 11.2)

7. Which statement is not true?

Ans: (a) 1 mole of Na2CO3 contains same number of Na+ cations as CO32- anions

8. Which one of the following molecular formulas is not an empirical formula?

Ans: (c) C6H9O3   (this can be represented as C2H3O)

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