Instructions 1. Take a chunk of chalk and measure its mass on the balance: 2. Go outside and draw something on the sidewalk. 3. Go back in class and weigh the unused chalk: 4. Based on the initial mass of the chalk and the mass at the end, calculate how many grams of chalk you left out on the sidewalk: 5. Write down the molecular formula of the chalk: 6. Get the masses of the atoms: 7. Calculate the chalk's molar mass: 8. Using this data, calculate: a. How many moles of chalk did you leave on the sidewalk? b. How many molecules of chalk did you leave on the sidewalk? c. How many atoms of calcium did you use? d. How many atoms of carbon did you use? e. How many atoms of oxygen did you use?

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Instructions 1. Take a chunk of chalk and measure its mass on the balance: 2. Go outside and draw something on the sidewalk. 3. Go back in class and weigh the unused chalk: 4. Based on the initial mass of the chalk and the mass at the end, calculate how many grams of chalk you left out on the sidewalk: 5. Write down the molecular formula of the chalk: 6. Get the masses of the atoms: 7. Calculate the chalk's molar mass: 8. Using this data, calculate: a. How many moles of chalk did you leave on the sidewalk? b. How many molecules of chalk did you leave on the sidewalk? c. How many atoms of calcium did you use? d. How many atoms of carbon did you use? e. How many atoms of oxygen did you use?

Answer 1

### a. 0.217 mol ### b. $ 1.31 \times 10^{23} $ molecules ### c. $ 1.31 \times 10^{23} $ atoms of calcium ### d. $ 1.31 \times 10^{23} $ atoms of carbon ### e. $ 3.93 \times 10^{23} $ atoms of oxygen

Answer 2

## Step 1: Calculate mass of chalk left on the sidewalk ### Subtract the final mass of the chalk from the initial mass. $\text{Mass left on the sidewalk} = 26.77 \, \text{g} - 5.05 \, \text{g} = 21.72 \, \text{g} $ ## Step 2: Calculate the number of moles of chalk left on the sidewalk ### Use the molar mass of chalk to convert the mass to moles. $n = \frac{m}{M} = \frac{21.72 \, \text{g}}{100.089 \, \text{g/mol}} = 0.217 \, \text{mol} $ ## Step 3: Calculate the number of molecules of chalk left on the sidewalk ### Use Avogadro's number to convert moles to molecules. $N = n \times N_A = 0.217 \, \text{mol} \times 6.022 \times 10^{23} \, \text{mol}^{-1} = 1.31 \times 10^{23} \, \text{molecules} $ ## Step 4: Calculate the number of atoms of calcium used ### Since there is 1 calcium atom per molecule of $ \mathrm{CaCO}_{3} $, the number of calcium atoms equals the number of molecules. $N_{Ca} = N = 1.31 \times 10^{23} \, \text{atoms} $ ## Step 5: Calculate the number of atoms of carbon used ### Since there is 1 carbon atom per molecule of $ \mathrm{CaCO}_{3} $, the number of carbon atoms equals the number of molecules. $N_C = N = 1.31 \times 10^{23} \, \text{atoms} $ ## Step 6: Calculate the number of atoms of oxygen used ### Since there are 3 oxygen atoms per molecule of $ \mathrm{CaCO}_{3} $, multiply the number of molecules by 3. $N_O = 3 \times N = 3 \times 1.31 \times 10^{23} = 3.93 \times 10^{23} \, \text{atoms} $

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