# Using Avogadro's Number

How many H2O molecules are there in a snowflake weighing 1 mg?

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Snowflakes are made of water, H2O. First, we need to find the mass of one mole (Avogadro's number or 6.022 x 10^23) of H2O molecules. To obtain this number, first look up the atomic masses for H and O ...

Stoichiometry Problems

Please see the attached file for the complete problems.

"Activity - Stoichiometry Exercises"

1. 1a. How many atoms are in 12 molecules of glucose.

1a. How many atoms are in 12 molecules of glucose, C6H12O6 ?

Use exact value for this answer.

24

2. 1b. How many moles of fluorine gas (F<sub>2</sub> molecule)?

1b. How many moles of fluorine gas (F2 molecule) are present in 55.0 grams of fluorine (F2) ?

Use three significant figues and express your answer.

1.45

3. 1c. What is the mass (g) of a single molecule of CO<sub>2</sub>

1c. What is the mass (g) of a single molecule of CO2 ? Hint: Express your answer in terms of grams per molecule.

Use three significant figues and express your answer in exponential notation.

0.0000000000249 = 2.49 e -11

1.

4. 1d. What is the atomic mass (atomic weight, g/mol) of an element.

1d. What is the atomic mass (atomic weight, g/mol) of an element that weighs 9.12 x 10-23 g ?

Round off your answer to the tenth of a gram/mole.

1.

5. 1e. Mole and Avogadro's Number: C8H9O4

01e. What is the mass (grams) of 0.216 mol of C8H9O 4 ?

Round off to the tenth of a gram.

1.

6. 2a. Balancing Equation and the Mole Concept

2a. Balance the equation and determine the number of moles of potassium chlorate (KClO3) required if 6 moles of potassium chloride and 9 of oxygen is produced from its decomposition.

Type in the moles of potassium chlorate.

Your answer should be an exact number.

1.

7. 2b. Balancing Equation and the Mole Concept

2b. How many moles of H2O will be produced from the complete combustion of 4.4g of C3H8 ?

Round off your answer to the hundredth of a mole.

1.

8. 2c. Balancing Equation and the Mole Concept

2c. A sample of ammonium dichromate (NH4)2Cr2O7, contains 2.25 mol of hydrogen atoms. What is the number of moles of oxygen atom in the sample?

Round off your answer to the tenth of a mole.

1.

9. 2d. Balancing Equation and the Mole Concept

2d. Balance the equation and determine the mass (grams) of nitrogen dioxide produce when 102.0 grams of ammonia reacts with excess oxygen to produce nitrogen dioxide and water.

Round off your answer to a tenth of a gram.

1.

10. 3a. Mass of hydrogen

3a. Calculate the mass (grams) of hydrogen formed when 25.00 g of aluminum reacts with excess HCl. The other product from this reaction is aluminum chloride.

Use four significant figures in your final answer.

1.

11. 3b. Mass of ammonia

3b. Carbon dioxide, CO2, and ammonia, NH3, combines together to form urea, CH4N2O, plus water. Write a balanced equation and calculate the mass of ammonia in grams that would be needed to make 2.0 moles of urea.

Use two significant figures.

1.

12. 3c. Grams of oxygen

3c. How many grams of oxygen are required to burn the 14.4 g of C5 H12 ?

Round off your answer to the tenth of a gram.

1.

13. 3d. Moles of oxygen

3d. How many moles of oxygen are needed to produce 11.0 g of P4 O6 from phosphorus

Round off to a thousandth of a mole.

1.

14. 3e. Percent yield of Iron.

3e. What is the percent yield for a reaction when 6.50 grams of Fe2 O3 combines with carbon monoxide to produce 3.85 g of iron ? (not balanced) __Fe2O3 + __CO ---> __Fe + CO2

Round off your answer to a tenth of a percent.

1.

15. 3f. Molecules of nitrogen dioxide.

3f. How many molecules of nitrogen monoxide is produced if 92.0 g of nitrogen dioxide is combine with excess water according to the following reaction? (Not balanced) __NO2(g) + __H2O(l)  __HNO3(g) + __NO(g)

Use three significant figues and express your answer in exponential notation.

2350 = 2.35 e + 03

1.