Molar Mass Calculation Calculate the molar mass of sodium carbonate, Na2CO3, using 4 sig figs from the periodic table for each element. Since you are adding, your answer should contain 5 significant figures. Make sure you include correct units for molar mass in your response or it will be marked incorrect. Grams to Moles A student measure out 145.3 grams of sodium carbonate on the electronic balance. Calculate the number of moles that represents. Include the correct sig figs and units in your response or it will be marked incorrect. nection AL Moles to Formula Units The 145.3 grams of sodium carbonate contains how many formula units? Use 4 sig figs in Avogadro’s number, and report the answer in scientific notation (formatted as “X 10^23”). Use the word “formula units” as the unit!
The Correct Answer and Explanation is :
calculate the molar mass of sodium carbonate (Na₂CO₃), we sum the molar masses of its constituent elements, each taken to four significant figures: Sodium (Na): 22. g/mol
- rbon (C):* 12.01 mol
- Oxn (O): 16.00 g/m
The form r sodium carbonate indicates it contains two sodium atoms, one carbon atom, and three oxygen atoms. Thus, the momass is calculated as follows: \begin{ali}text{Molar mass of Na}_2\text{CO}_3 &= (2 \times 22.99\, \text{g/mol}) + (1 \times 12.01\, \text{g/mol}) + (3 \times 16.00\, \text{g/mol}) \\ &= 45.98\, \text{g/mol} + 12.01\, \text{g/mol} + 48.00\, \text{g/mol} \\ &= 105.99\, \text{g/mol} \end{align*}
Since we are add lues, the result should be reported with five significant figures, yielding a molar mass of 105.99 g/mol.
Next, to determine mber of moles in a 145.3-gram sample of sodium carbonate, we use the formula: \text{Number of mol \frac{\text{Mass of sample (g)}}{\text{Molar mass (g/mol)}}
Substituting the known vas \text{Number of moles} = a145.3\, \text{g}}{105.99\, \text{g/mol}} \approx 1.3709\, \text{mol}
Here, the mass of the sample (13) has four significant figures, and the molar mass (105.99 g/mol) has five significant figures. When performing division, the resulould be reported with the same number of significant figures as the value with the fewest significant figures—in this case, four. Therefore, the number of moles is 1 mol.
To find the number of formula units ine45.3-gram sample, we multiply the number of moles by Avogadro’s number. Avogadro’s number is exactly 6.02214076es10236.02214076 es 10^{23} mol⁻¹, but for this calculation, we’ll use four significant figures: 6.022×10236.022 \times 10^{23} mol⁻¹. Number of formula units=Neof moles×Avogadro’s number\text{Number of formula units} = \text{Neof moles} \times \text{Avogadro’s number}
Substituting the values: Number of fu units=1.371 \textl×6.022×1023 mol−1≈8.256×1023 formula units\text{Number of fu units} = 1.371\, \textl\times 6.022 \times 10^{23}\, \text{mol}^{-1} \approx 8.256 \times 10^{23}\, \text{formula units}
The number of moles (1.371 mol) has four significantges, and Avogadro’s number (6.022 × 10²³ mol⁻¹) also has four significant figures. Therefore, the result should be reported with four signint figures. Thus, the 145.3-gram sample of sodium carbonate contains aximately 8.256 × 10²³ formula units.
In summary, the molar mass of sodium carbonate is 105.99 g/. 145.3-gram sample represents 1.371 moles, which corresponds tproximately 8.256 × 10²³ formula units. These calculations are fundamental in stoichiometry, allowing ches to relate the mass of a substance to the number of particles it contains, facilitating the quantitative analysis of chemical reactions.