Percent Composition Parts of a Whole. Percent Short for per centum …”by the hundred” Part of a whole If there are 10 people in a room and 4 of them have.

Presentation on theme: "Percent Composition Parts of a Whole. Percent Short for per centum …”by the hundred” Part of a whole If there are 10 people in a room and 4 of them have."— Presentation transcript:

1 Percent Composition Parts of a Whole

2 Percent Short for per centum …”by the hundred” Part of a whole If there are 10 people in a room and 4 of them have blue eyes, what percentage of people have blue eyes?

3 Composition Chemical formula Molar mass

4 Percent Composition Write the formula Find the molar mass Determine the percentage of the part in question

5 Problem #1 Determine the percent composition of water.

6 Problem #1—Step 1 Write its formula ▫ H 2 O

7 Problem #1—Step 2 Determine its molar mass ▫ H—2 x 1.01 = 2.02 ▫ O—1 x 16.00 = 16.00 18.02 g/mol

8 Problem #1—Step 3 Determine the portion that each element makes up by its mass and multiply by 100…determine the percent composition ▫ H—2 x 1.01 = 2.02 x 100 = 11.2% H 18.02 ▫ O—1 x 16.00 = 16.00 x 100 = 88.8% O 18.02

9 Problem #2 Determine the percent composition of aluminum carbonate.

10 Problem #2—Step 1 Write its formula ▫ Al 2 (CO 3 ) 3

11 Problem #2—Step 2 Determine its molar mass ▫ Al—2 x 26.98 = 53.96 ▫ C—3 x 12.01 = 36.03 ▫ O—9 x 16.00 = 144.00 233.99 g/mol

12 Problem #1—Step 3 Determine the percent composition ▫ Al—2 x 26.98 = 53.96 x 100 = 23.1% Al 233.99 ▫ C—3 x 12.01 = 36.03 x 100 =15.4% C 233.99 ▫ O—9 x 16.00 = 144.00 x 100 =61.5% O 233.99

13 Problem #3 A compound contains only copper and chloride ions. It is found to be 47.3% copper. Determine the formula of the compound.

14 Problem #3—Step 1 Determine the possible formulas ▫ Copper can have charges of 1+ or 2+ ▫ So, your choices are: CuCl and CuCl 2

15 Problem #3—Step 2 Determine both molar masses ▫ Cu—1 x 63.55 = 63.55 ▫ Cl—1 x 35.45 = 35.45 99.00 g/mol ▫ Cu—1 x 63.55 = 63.55 ▫ Cl—2 x 35.45 = 70.90 134.45 g/mol

16 Problem #3—Step 3 Determine the percentage of copper in each. ▫ Cu—1 x 63.55 = 63.55 x 100 = 64.2% Cu 99.00 ▫ Cu—1 x 63.55 = 63.55 x 100 = 47.3% Cu 134.45 So, the answer is CuCl 2

17 Problem #4 A compound is known to contain 41.7% magnesium. Determine if the compound is magnesium fluoride, magnesium hydroxide, or magnesium oxide.

18 Problem #4—Step 1 Determine the formulas ▫ MgF 2 ▫ Mg(OH) 2 ▫ MgO

19 Problem #4—Step 2 Determine all three molar masses ▫ Mg—1 x 24.31 = 24.31 ▫ F—2 x 19.00 = 38.00 62.31 g/mol ▫ Mg—1 x 24.31 = 24.31 ▫ O—2 x 16.00 = 32.00 ▫ H—2 x 1.01 = 2.02 58.33 g/mol ▫ Mg—1 x 24.31 = 24.31 ▫ O—1 x 16.00 = 16.00 40.31 g/mol

20 Problem #4—Step 4 Determine the percentage of magnesium in each. ▫ Mg—1 x 24.31 = 24.31 x 100 =39.0% Mg 62.31 ▫ Mg—1 x 24.31 = 24.31 x 100 = 41.7% Mg 58.33 ▫ Mg—1 x 24.31 = 24.31 x 100 =60.3% Mg 40.31

21 Problem #4—Answer Mg(OH) 2

22 Practice, practice, practice