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Moles and massChemistryHigh schoolabout 1:24

How many moles are in 45 g of C6H12O6?: animated lesson

A narrated, step-by-step moles and mass video lesson with captions. Final answer: M(C6H12O6) = 180.156 g/mol; 45 g = 0.249784 mol.

Video with a synthetic English voice and captions. Pick another language for subtitles in that language, or open the interactive version.

Video narrated by a synthetic voice (Piper TTS, en_US-ljspeech-high voice (LJ Speech dataset, public domain)); the steps come from our maths engine and the answer was checked independently. Download MP4 (0.6 MB) · Captions (WebVTT)

Steps on screen

  1. 1. The problem
    Worked example
    How many moles are in 45 g of C6H12O6?
  2. 2. Steps, part 1
    1. C:6,H:12,O:6\text{C}: 6,\quad \text{H}: 12,\quad \text{O}: 6
      Count the atoms of each element
    2. C=12.011,H=1.008,O=15.999\text{C} = 12.011,\quad \text{H} = 1.008,\quad \text{O} = 15.999
      Look up each atomic weight (g/mol)
    3. 6×12.011=72.06612×1.008=12.0966×15.999=95.9946 \times 12.011 = 72.066 \\ 12 \times 1.008 = 12.096 \\ 6 \times 15.999 = 95.994
      Multiply each count by its atomic weight
    4. M=72.066+12.096+95.994=180.156 g/molM = 72.066 + 12.096 + 95.994 = 180.156\ \text{g/mol}
      Add the contributions
  3. 3. Steps, part 2
    1. %C=72.066180.156×100≈40.00%%H=12.096180.156×100≈6.71%%O=95.994180.156×100≈53.28%\%\text{C} = \frac{72.066}{180.156} \times 100 \approx 40.00\% \\ \%\text{H} = \frac{12.096}{180.156} \times 100 \approx 6.71\% \\ \%\text{O} = \frac{95.994}{180.156} \times 100 \approx 53.28\%
      Mass percent of each element
    2. n=mM=45 g180.156 g/mol≈0.249784 moln = \frac{m}{M} = \frac{45\ \text{g}}{180.156\ \text{g/mol}} \approx 0.249784\ \text{mol}
      Convert the sample mass to moles
    3. N=nNA≈0.249784×6.02214076×1023≈1.5042×1023N = n N_A \approx 0.249784 \times 6.02214076\times10^{23} \approx 1.5042\times10^{23}
      Number of formula units
  4. 4. The answer
    M=180.156 g/molM = 180.156\ \text{g/mol}

    6×12.011 + 12×1.008 + 6×15.999 = 180.156 g/mol

  5. 5. Check
    • Percent composition adds to 100.00%.
    • Elements: carbon ×6, hydrogen ×12, oxygen ×6.

Transcript

The problem. Here is the problem: How many moles are in 45 g of C6H12O6? Add the atomic weights of all 24 atoms in one formula unit of C6H12O6.

Steps, part 1. Count the atoms of each element. Subscripts multiply everything inside the brackets before them, and a hydrate coefficient multiplies the whole water (or other) unit. Look up each atomic weight (g/mol). IUPAC standard atomic weights (abridged, conventional values). Multiply each count by its atomic weight. Add the contributions.

Steps, part 2. Mass percent of each element. Convert the sample mass to moles. Number of formula units.

The answer. So the answer is M(C6H12O6) equals 180.156 g/mol; 45 g equals 0.249784 mol. The molar mass is the mass of one mole of formula units. It equals the sum of the atomic weights of every atom in the formula, and numerically matches the formula mass in daltons (u).

Check. Percent composition adds to 100.00 percent. Elements: carbon times 6, hydrogen times 12, oxygen times 6.

About moles and mass

Convert between grams, moles and particles with molar mass and Avogadro's number.

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How many moles are in 45 g of C6H12O6?: Step-by-Step Lesson