# Chemistry - Molecular Formula

A carbohydrate contains 39.56% C, 7.75% H, and 52.70% O by mass. A solution of 11.3 g of this carbohydrate in 375 g of ethanol has a boiling point of 78.49 deg C. The boiling point of ethanol is 78.29 deg C, and Kb for ethanol is 1.23 deg C*kg/mol. What is the molecular formula of this carbohydrate?

So this is what I have so far:

C: 39.56/12.01 = 3.2939 mol = 3.2939/3.2937 = 1.00

H: 7.75/1.008 = 7.6885 mol = 7.6885/3.2937 = 2.33 = 2

O: 52.70/16 = 3.2937 mol = 3.2937/3.2937 = 1

So the empirical formula is CH2O, and the formula mass is 30.026 g/mol

Then,

(78.48-78.29)/1.23 = 0.1626016 mol/kg
n=0.1626016 mol/kg*375*(1kg/1000g) = 0.0609756 mol
M=11.3g/0.0609756 mol = 185.32 g/mol
185.32/30.026 = 6.172 = 6 formula units per molecule

Meaning the molecular formula should be C6H12O6. But the homework program I'm using says this is incorrect. Can you help me see where I might have gone wrong? Thanks

1. 👍 0
2. 👎 0
3. 👁 147
1. Nevermind, I got it.

I totally forgot about multiplying empirical formulas to the nearest whole number. It's actually: C3H7O3

Which makes the formula mass 91.086

Which makes the molecular formula C6H14O6

1. 👍 0
2. 👎 0
posted by Jamie

1. 👍 0
2. 👎 0

## Similar Questions

1. ### Chemistry

a solution of 4.65 of a carbohydrate in 100.0g of water has a density of 1.016g/mL and an osmotic pressure of 3.18 atm at 20.0 degrees celcius. calculate the molar mass of the carbohydrate.

asked by Amy on February 15, 2011
2. ### physics

How many grams of carbohydrate does a person of mass 75 kg need to metabolize to climb five flights of stairs (15 m height increase)? Each gram of carbohydrate provides 17.6 kJ of energy. Assume 10.0% efficiency—that is, 10.0%

asked by Nasir on June 8, 2012
3. ### chemistry

By using the data in this question, estimate how much oxygen a person requires on average in a life time and how far a motor can go using the same amount of oxygen. the typical daily food requirement of a person can be considered

asked by Anonymous on June 3, 2012
4. ### Chemistry

By using the data in this question, estimate how much oxygen a person requires on average in a life time and how far a motor can go using the same amount of oxygen. the typical daily food requirement of a person can be considered

asked by Cherie on June 3, 2012
5. ### Chemistry

The following questions concern the iconic Nestle Toll House Chocolate Chip Cookie recipe, shown below: 2 1/4 cups all-purpose flour 1 teaspoon baking soda 1 teaspoon salt 1 cup butter or margarine, softened 3/4 cup granulated

asked by qwerty on October 10, 2013
6. ### probability and statistics

welsh, davis, burke, and williams (2002) conducted a study to evaluate the effectiveness of a carbohydrate-electrolyte drink on sports performance and endurance. experienced athletes were given either s carbohydrate-electrolyte

asked by kiera on January 6, 2012

How many grams of carbohydrate does a person of mass 75 kg need to metabolize to climb five flights of stairs (15 m height increase)? Each gram of carbohydrate provides 17.6 kJ of energy. Assume 10.0% efficiency—that is, 10.0%

asked by Nasir on June 11, 2012
8. ### Phsyics Plz Help

How many grams of carbohydrate does a person of mass 75 kg need to metabolize to climb five flights of stairs (15 m height increase)? Each gram of carbohydrate provides 17.6 kJ of energy. Assume 10.0% efficiency—that is, 10.0%

asked by Nasir on June 11, 2012
9. ### Inferential Statictics

Welsh, Davis, Burke, and Williams (2002) conducted a study to evaluate the effectiveness of a carbohydrate-electrolyte drink on sports performance and endurance. Experienced athletes were given either a carbohydrate-electrolyte

asked by Summer on February 27, 2012
10. ### Chem

A patient receives 3.2 L of glucose solution intravenously (IV). If 100. mL of the solution contains 5.0 g of glucose (carbohydrate), how many kilocalories did the patient obtain from the glucose solution? *If anyone could help me

asked by Lori on September 3, 2018

More Similar Questions