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Chemistry

The document contains practice problems related to stoichiometry and percent composition by mass. It begins with questions about moles, molecules, and chemical formulas. It then provides the answers to calculating percent composition of NaCl, glucose (C6H12O6), and the element with the highest percentage by mass in Mg(OH)2. Next, it asks the reader to calculate the percent carbon and oxygen in aspirin (C9H8O4) by mass. Finally, it gives an activity to determine the percent sodium in various snack foods by looking at food labels.

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Earl Cris Riggs
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79 views1 page

Chemistry

The document contains practice problems related to stoichiometry and percent composition by mass. It begins with questions about moles, molecules, and chemical formulas. It then provides the answers to calculating percent composition of NaCl, glucose (C6H12O6), and the element with the highest percentage by mass in Mg(OH)2. Next, it asks the reader to calculate the percent carbon and oxygen in aspirin (C9H8O4) by mass. Finally, it gives an activity to determine the percent sodium in various snack foods by looking at food labels.

Uploaded by

Earl Cris Riggs
Copyright
© © All Rights Reserved
We take content rights seriously. If you suspect this is your content, claim it here.
Available Formats
Download as DOCX, PDF, TXT or read online on Scribd
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6. In which of the following quantities will two isotopes of an element have different values?

A. Atomic number C. Number of protons


B. Mass number D. Number of electrons
7. Which of the following information on the number of protons (p), electrons (e) and neutrons
(n) is correct for 92 U238?
A. 92 p, 92 n, 92 e C. 238 p, 146 n, 238 e
B. 92 p, 146 n, 92 e D. 146 p, 82 n, 92 e
8. What is the mass number of an atom which has 11 protons, 11 electrons, and 12 neutrons?
A. 11 C. 22
B. 12 D. 23
6. How many molecules of H2O are there in 1 mole of water molecules?
Answer: 6.022 x 1023 H2O molecules
7. How many molecules of carbon dioxide, CO2, are there in 2.648 moles CO2?

8. How many atoms of oxygen are there in 2.648 moles CO2?

="3.189"x"10"24"O"atoms"
9. Determine the number of moles of ammonia, NH3, in 8.254 x 1025 molecules of ammonia.

="137.1"moles"NH3"

Percent Composition by Mass


Ask them to answer the following practice exercises:
I. Calculate the percent composition of NaCl.
II. The chemical formula of glucose is C6H12O6. Determine its percent composition.
III. Which element comprising Mg(OH)2 has the highest percentage by mass?
1. 39.34% Na, 60.66% Cl
2. 39.99% C, 6.727% H, 53.28% O
3. O; the composition is 41.68% Mg, 54.89% O,
and 3.46% H

Aspirin has the molecular formula C9H8O4.


_____1. What is the % C in aspirin by mass in aspirin?
_____2. What is the % O in aspirin by mass in aspirin?
Answer Key
1. 60.00%
2. 35.53%

Activity

Determine the % sodium in snack food


Look at the food labels of some snack food like potato chips, peanuts, popcorn, etc. Fill up the
table below.
1. Identify your chosen snack food and brand.
2. Get the amount in grams of one serving of the snack food.
3. Get the amount of sodium in mg in one serving of the snack food.

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