Objectives:
apply the concept of percentage composition in choosing grocery items. realize that the amount of substance intake can be monitored with the use
of percentage composition. Materials:
DRAFT
March 31, 2014
77
Procedure:
1. Get 3 samples of containers or package of grocery items such as canned goods, snacks and beverages.
2. List the substances written as content/ingredients on the label. Choose 2 substances from each type of grocery item.
3. Research from a chemistry book or from the internet the chemical formula of the substances on your list.
4. Compute for the percentage composition of the substances you have listed.
Q1. Based on this activity, what food do you regularly consume which give your body a lot of carbon (C) atoms and sodium (Na) ions?
Q2. Are these good for your body? Why? Research on how much of these types of food are recommended for your age group.
Q3. In what other ways can you make use of the concept on percentage composition? Knowledge about percentage composition is useful in choosing the best fertilizer that gives higher amount of nitrogen and potassium in the soil. Aside from this, it will help us to be a wise consumer because it is a good basis of choosing the food product we need to eat based on its content. Whenever you buy t-shirt, it is good to check whether it is 100% cotton or just 75% cotton. In terms of product development, percentage composition will indicate the correct amount of substances needed in order to produce the expected product. For example, if a manufacturing company wants to produce resin it will not be formed if they do not know the correct percentage of every component.
Summary:
It is important that you remember the following ideas from this module:
Different kinds of materials with the same number of particles have different masses.
One mole contains the Avogadro’s number of particles equal to 6.02 x 10 23.
Different substances with the same number of moles have the same number of particles but they have different masses.
Molar mass is the mass of one mole of a substance expressed in grams.
The molar mass of a monatomic element like Na, Li, Mg is numerically equal to its atomic mass expressed in grams.
The mass of the substance divided by its molar mass gives the number of moles of the substance.
The number of moles multiplied by the Avogadro’s number gives the number of particles.
DRAFT
March 31, 2014
78 Percentage composition of a compound tells you the percentage of the mass
made up by each element in a compound
Glossary:
Avogadro’s Number the number equal to 6.02 x 10 23 which refers to the number of
atoms or ions or molecules equal to 1 mole
chemical formula a combination of the symbol of elements and subscript numbers representing a compound
molar mass the mass of one mole of a substance mole SI unit to express the amount of a substance
molecule the smallest unit of a substance that retains its physical and chemical properties, it may be composed of one kind of atom or two or more kinds of atoms bonded together.
percentage composition the percentage by mass of each element in a compound
Summative Assessment
Direction: Choose the letter of the correct answer.
1. The label of the dark chocolate indicates that its mass is 150g and it is 70% cacao, if you consume the whole chocolate bar, how much cacao did you eat?
a. 105 g cacao b. 45 g cacao c. 100 g cacao d. 50 g cacao 2. What is the representative particle of ionic compounds?
a. atom b. ion
c. molecule d. formula unit
3. How many particles are there in one mole of any kind of substance? a. 3.01 x 1023 b. 6.02 x 1023
DRAFT
March 31, 2014
79 4. Moth balls (paradichlorobenzene-C6H4Cl2) are used as cockroach repellent. It is often
placed inside the cabinet. If 1piece of moth ball weighs 5.0g and your mother put 3 pieces in your cabinet, how many molecules of paradichlorobenzene-C6H4Cl2 (Molar
Mass = 147.00 g/mol) will be circulating inside your cabinet considering all the moth balls have sublimed?
a. 6.02 x 10 22 molecules of C6H4Cl2
b. 6.02 x 10 23 molecules of C6H4Cl2
c. 6.14 x 10 22 molecules of C6H4Cl2
d. 6.14 x 10 23 molecules of C6H4Cl2
5. Who among the following students describes the result of the activity on counting by weighing correctly?
Ann – Different sets of materials having the same mass have different number of pieces.
Dan – Different sets of materials have the same number of pieces and the same mass.
Tom - The same sets of materials, have the same number of pieces but different masses.
a. Ann b. Dan
c. Tom d. none of them
6. The roots of the plants absorb the nutrients from the soil. For the farmers, it is important to strengthen the root system of their plants to ensure its growth. Potassium is the mineral responsible for a healthy root system. If you were a farmer, which of the following fertilizers are you going to use?
a. K2SO4 b. K2O
c. KCl d. K2CO3
7. Methane (CH4Molar Mass = 16.04 g/mol) is one of the greenhouse gases. If 32.08 g of CH4 is released in the atmosphere, how many molecules of CH4 are added in the
atmosphere?
a. 1.20 x 1024 b. 1.20 x 1023
c. 6.02 x 1024 d. 6.02 x 1023
8. The presence of SO2 in the atmosphere causes acid rain. How many percent of sulfur is present in SO2 (Molar Mass = 64.07g/mole)?
a. 40.00% b. 49.95%
DRAFT
March 31, 2014
80 9. Arrange the following substances from the lightest to the heaviest:
Cl2; CH4; H2O; NH3; N2
a. H2O< NH3< N2< CH4< Cl2 b. CH4< NH3< H2O< N2< Cl2
c. N2< Cl2< H2O< CH4<NH3 d. NH3< CH4< Cl2< H2O< N2
10. Why is mole concept important?
a. It is useful when converting between grams and atoms or molecules. b. It gives us a convenient way to express large numbers
c. It can be applied to any type of particle representative d. All of the above
11. Ammonium nitrate (NH4NO3 Molar Mass = 80.06g/mole) is a substance use to
produce dinitrogen monoxide (N2O), a dental anesthetic. Determine the mass percent of
N in ammonium nitrate?
a. 35.00% b. 40.65%
c. 39.50% d. 43.68%
12. People usually use hydrogen peroxide (H2O2 Molar Mass = 34.02 g/mole) to clean
their wounds. If Cheska used 1.0 g of H2O2 to clean her wound, how many mole of H2O2
did she use?
a. 0.035 mole b. 0.030 mole
c. 0.029 mole d. 0.025 mole
13. In cold areas, many fish and insects, including the common housefly produce large amounts of glycerol (C3H8O3 Molar Mass = 92.11 g/mole) to lower the freezing point of
their blood. How many percent of oxygen is present in glycerol?
a. 52.11% b. 50.11%
c. 51.11% d. 53.11%
14. Ethyl butanoate (C3H7COOC2H5) is the substance responsible for the aroma of
pineapple. What is the molar mass of ethyl butanoate?
a. 118.00 g/mole b. 117.12 g/mole c. 120.12 g/mole d. 116.18 g/mole
15. Calcium carbonate (CaCO3 Molar Mass = 100.09 g/mole ) is an antacid used to
neutralize extra acid in the stomach. Lorie is prescribed by the doctor to take 250mg- tablet of CaCO3 three times a day. How many moles of CaCO3 will Lorie consume for 3
days?
a. 0.0252 moles b. 0.0225 moles
DRAFT
March 31, 2014
81
References:
LeMay, E.H. Jr., Robblee, K.M., Brower, H., Douglas C. (1996). Chemistry Connections to Our Changing World. New Jersey: Prentice Hall, Inc.
Magno, M., et. al. (2001). Practical Work in High School Chemistry Sourcebook for Teachers. Quezon City: UP National Institute for Science & Mathematics Education Development
Department of Education,.Culture and Sports.1992 Teaching Resource Package: S&T- Chemistry. PASMEP, AIDAB,UP-ISMED, DECS. Pasig: Author.
Silberberg, M. (1996). Chemistry: The Molecular Nature of Matter and Change. St. Louis: Mosby
Wilbraham, A.C., Staley, D. D., Matta, M. (1997). Chemistry ( 4thed) New York: Addison-
Wesley Pub.
Wilbraham, A.C., Staley, D.D., Matta, M.S. & Waterman, E.L. (2007). Chemistry, Teacher’s Ed. Boston, Massachusetts:Pearson, Prentice Hall, Inc.