To calculate the molecular weight of a polymer sample, you need to determine the total weight of each molecular weight species present and then use these to calculate an average molecular weight. Here's a step-by-step breakdown:
Calculating Total Weight Per Molecular Weight
The first step is to find the total weight contributed by each type of molecule within the polymer sample. This is achieved by:
- Identifying the Different Molecular Weights: Determine all the different molecular weights present in the polymer sample. For example, molecules might be found with a weight of 550,000, as per the reference.
- Counting the Number of Molecules at Each Weight: For each molecular weight, find out how many molecules of that weight are present. The reference indicates, for instance, that there are 13 molecules with a weight of 550,000.
- Multiplying Molecule Count by Molecular Weight: Multiply the number of molecules by their corresponding molecular weight. Using the reference, for molecules weighing 550,000, the total weight is calculated as 13 molecules x 550,000 = 7,150,000.
Example Calculation and Table
Let's create an example using hypothetical data along with the reference information:
| Molecular Weight | Number of Molecules | Total Weight (Number of Molecules * Molecular Weight) |
|---|---|---|
| 550,000 | 13 | 7,150,000 |
| 600,000 | 8 | 4,800,000 |
| 700,000 | 5 | 3,500,000 |
This approach is crucial for obtaining the correct average, as simply adding the individual molecular weights would not provide a meaningful reflection of the sample's overall molecular weight.
Calculating Average Molecular Weight
Once you’ve calculated the total weight for each molecular weight group, the next step would be to sum all these total weights and divide by the total number of molecules. This would provide a number average molecular weight. However, the question only asks how to calculate total weight of molecules, so we will stop here.
Summary
- To find the total weight of a molecular weight species of a polymer: multiply the number of molecules of a given molecular weight by the value of that molecular weight.
