The Correct Answer and Explanation is:
2105 grams of PtSe
To convert a given number of moles of a substance into its equivalent mass in grams, you must use the substance’s molar mass as a conversion factor. Molar mass is a crucial concept in chemistry that defines the mass of one mole of any given chemical compound. The process involves two main steps: first, determining the molar mass of the compound, and second, performing the conversion calculation.
Step 1: Calculate the Molar Mass of Platinum Selenide (PtSe)
The molar mass of a compound is the sum of the molar masses of all the atoms in its chemical formula. These individual atomic masses are found on the periodic table. The formula PtSe indicates that one molecule of the compound contains one atom of platinum (Pt) and one atom of selenium (Se).
- From the periodic table, the molar mass of Platinum (Pt) is approximately 195.084 grams per mole ( g/mol ).
- The molar mass of Selenium (Se) is approximately 78.971 grams per mole ( g/mol ).
To find the molar mass of the entire compound, we add these values:
Molar Mass of PtSe = Molar Mass of Pt + Molar Mass of Se
Molar Mass of PtSe = 195.084 g/mol + 78.971 g/mol = 274.055 g/mol .
This value means that one mole of PtSe has a mass of 274.055 grams.
Step 2: Convert Moles to Grams
With the molar mass calculated, we can now convert the given moles to grams using the relationship:
Mass (grams) = Moles × Molar Mass ( g/mol )
The problem provides the number of moles as 7.680. We multiply this by the molar mass we just calculated:
Mass = 7.680 mol × 274.055 g/mol
Mass = 2104.7424 g
Step 3: Apply Significant Figures
The final step is to ensure the answer is presented with the correct number of significant figures. The initial value given in the problem, 7.680 moles, has four significant figures (the 7, 6, 8, and the trailing zero after the decimal point are all significant). Therefore, our final answer must be rounded to four significant figures to reflect the precision of the starting measurement.
Looking at the calculated result, 2104.7424, the first four digits are 2, 1, 0, and 4. We look at the fifth digit, which is 7. According to rounding rules, if the digit is 5 or greater, we round up the previous digit. Since 7 is greater than 5, we round up the 4 to a 5.
Therefore, 2104.7424 g rounded to four significant figures is 2105 g.
