Let’s Celebrate the

National Molar Day

Getting the Molar Mass

A Strategic Intervention Material in Science 9

Prepared by: JOHN FLORENTINO E. ECHON, Science Teacher I

Presented to: LENIE N. ELAMPARIO, Principal II

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LEAST MASTERED SKILLS:MOLAR MASS

Learning competencies:use the mole concept to express mass of substances; specifically to calculate the molar mass of a given compound.Learning code: S9MT-IIi-19

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THE GUIDE CARDTa

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Substances take up space and have mass. Molecules are also substances, and in experiments, it is important to measure their amounts accurately. How do we normally measure molecules? In the science laboratory, we use an analytical balance to measure their weight in grams. For instance, we already know the number of moles that we need, but we do not know how many grams we need. The good thing is, scientists have come up with a way for us to figure out how many grams we need from the number of moles. To do this, we need to use the molar mass.The molar mass, also known as molecular weight, is the sum of the total mass in grams of all the atoms that make up a molecule per mole. Its unit is in grams per mole.

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Molar Mass from Periodic Table

Molar mass is the atomic mass expressed in grams/mol

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How to Find the Molar Mass For Compounds

Compounds are substances that are made up of more than one element. For example, the following are common compounds:The compound NaCl is made up of two elements, namely, Na (sodium) and Cl (chlorine). Let us use NaCl as our first example on how to calculate the molar mass for the compounds. The first thing we need to do is to find Na and Cl in the periodic table:

Element Atomic Mass

Number of Atoms Total Mass

Na 23 g

Cl 35.5 g

NaCl

MOLAR MASS OF A COMPOUND

Find the atomic masses of individual elements in the periodic tableThe first thing we need is to find the individual atomic masses for each element (Na and Cl). The picture above shows the elements Na and Cl in the periodic table. The numbers we will be looking for are those at the top left for each element -- these represent the atomic mass. The element Na (sodium) has an atomic mass of 22.98976 g/mol. The element Cl (chlorine) has an atomic mass of 35.453 g/mol.

Step 1Step 1

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Count how many atoms there are for each elementFor the compound NaCl, since there are no subscripts (small numbers at the bottom of each element), that means there is only one Na and only one Cl atom for this compound.

Element Atomic Mass Number of Atoms Total Mass

Na 23 1

Cl 35.5 1

NaCl

Step 2

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Step. 3 Find the molar mass by multiplying the atomic mass (g) of an element to the number of atoms. ADD the total mass to get the molar mass of the compound

Element Atomic Mass

Number of Atoms Total Mass

Na 23 g 1 23

Cl 35.5 g 1 35.5

NaCl 58.5 g/mol

Step 3

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8The molar mass of a compound is the sum of the molar masses of the elements in the formula.

Example: Calculate the molar mass of CaCl2.Element Atomic

MassNumber of

AtomsTotal Mass

Ca 40.1 g 1 40.1 g/molCl 35.5 g 2 71.0 g/mol

CaCl2 111.1 g/mol

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Molar Mass of K3PO4Calculate the molar mass of K3PO4.

Element Atomic Mass

# of atoms Total Mass in K3PO4

K 39.1 g 3 117.3 g/molP 31.0 g 1 31.0 g/molO 16.0 g 4 64.0 g/mol

K3PO4 212.3 g/mol

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ACTIVITY CARDWHAT’S THE MESSAGE?

Learning competencies:use the mole concept to express mass of substances; specifically to calculate the molar mass of a given compound.Learning code: S9MT-IIi-19

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Activity # 1WHAT’S THE MESSAGE?

The Given: Below are the given compound. Get their molar mass.1. NaBr 2. PbSO4

3. Ca(OH)2

4. Na 3(PO)45. (NH4)2CO3

6. C6H12O6

7. Fe3(PO4)28. (NH4)2S9. Zn(C2H3O2)2

Direction: Calculate the molar mass of the given compound. Each molar mass represents a code which can be found inside the box below.

_ _ _ _ _ _ _ _ _ _ _ _ _1 2 3 4 5 6 4 7 6 8 2 9 6

A (164.0 g/mol) R (96.0 g/mol)E (180.0 g/mol) S (68.1 g/mol)M (183.4 g/mol) U (74.1 g/mol)O (303.3 g/mol) W (357.4 g/mol)Y (102.9g/mol)

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AssessmeNt card Ta

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Assessment CardTIME’S UP!Direction: Find your partner and calculate the molar mass of the following compound. Your partner will serve as the timer. You have five minutes to do the task. Record the time and let your partner do the task too.

1. Al2S3

2. H2O 3. Na2O 4. CCl5

5. CO2

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eNrichmeNt card Ta

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ENRICHMENT CARDArrange the following compound in increasing molar mass.1. ZnCl2

2. NH3

3. Al2O3 4. C6H10O5

5. H2SO4

For additional activities, you may play the MOLAR BINGO. See attachment for the problems and the bingo card

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IT’S DONE! CONGRATULATIONS!15

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ACTIVITY #11. Y2. O3. U4. A5. R6. E7. W8. S

9. M

TIME’S UP!1. 150.2 g/mol2. 18 g/mol3. 62 g/mol4. 153.8 g/mol5. 44 g/mol

ENRICHMENT1. 136.3 g/mol2. 17g/mol3. 102g/mol4. 162g/mol5. 98.1g/mol

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Read me wheN YOU ARE DONE

RefereNce card Ta

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Reference CardAbistado et al.(2014). Science Link 9. Rex Bookstore. Manila Philippines. Pp. 173-176

For more practice problems please visit: misterguch.brinkster.net/PRA001.pdfpeople.uwec.edu/bhattas/ppt_ch4_ch5_b.pdf

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