Calculating Total Volatile Solids in Water Samples
Understanding the composition of water samples often involves determining the amount of dissolved and suspended solids present. Solids are typically classified based on whether they remain after drying at 103-105 °C (Total Solids) and whether they burn off when heated to 550 °C (Volatile Solids). The material remaining after heating at 550 °C is called Fixed Solids.
In this problem, we are given measurements related to determining these solids and asked to calculate the Total Volatile Solids concentration in milligrams per liter (mg/L).
Steps to Determine Total Volatile Solids Concentration
The calculation involves several steps using the provided weight measurements and the sample volume:
- Calculate the weight of Total Solids.
- Calculate the weight of Fixed Solids.
- Calculate the weight of Volatile Solids (which is the difference between Total Solids and Fixed Solids).
- Convert the weight of Volatile Solids from grams to milligrams.
- Convert the sample volume from milliliters to liters.
- Calculate the concentration of Total Volatile Solids in mg/L.
Analyzing the Provided Data for Solids Calculation
Let's break down the given data:
- Weight of empty dish = \(48.6212 \text{ g}\)
- Weight of dish and dry solids (after evaporation at 103-105 °C) = \(48.6432 \text{ g}\)
- Weight of dish and fixed solids (after heating at 550 °C) = \(48.6300 \text{ g}\)
- Volume of sample used = \(100 \text{ mL}\)
Step-by-Step Calculation of Total Volatile Solids
Step 1: Calculate the weight of Total Solids.
Total Solids are the residues left after evaporating the sample. This is found by subtracting the empty dish weight from the weight of the dish plus dry solids.
Weight of Total Solids = (Weight of dish + dry solids) - (Weight of empty dish)
\( \text{Weight of Total Solids} = 48.6432 \text{ g} - 48.6212 \text{ g} = 0.0220 \text{ g} \)
Step 2: Calculate the weight of Fixed Solids.
Fixed Solids are the inorganic residues remaining after the sample is heated at 550 °C. This is found by subtracting the empty dish weight from the weight of the dish plus fixed solids.
Weight of Fixed Solids = (Weight of dish + fixed solids) - (Weight of empty dish)
\( \text{Weight of Fixed Solids} = 48.6300 \text{ g} - 48.6212 \text{ g} = 0.0088 \text{ g} \)
Step 3: Calculate the weight of Volatile Solids.
Volatile Solids are the organic and other combustible materials that are driven off or decomposed by heating at 550 °C. This is the difference between Total Solids and Fixed Solids.
Weight of Volatile Solids = Weight of Total Solids - Weight of Fixed Solids
\( \text{Weight of Volatile Solids} = 0.0220 \text{ g} - 0.0088 \text{ g} = 0.0132 \text{ g} \)
Step 4: Convert the weight of Volatile Solids from grams to milligrams.
The required unit for concentration is mg/L, so we convert the weight from grams to milligrams using the conversion factor \(1 \text{ g} = 1000 \text{ mg}\).
\( \text{Weight of Volatile Solids (mg)} = 0.0132 \text{ g} \times 1000 \frac{\text{mg}}{\text{g}} = 13.2 \text{ mg} \)
Step 5: Convert the sample volume from milliliters to liters.
The required unit for volume in concentration is liters, so we convert the volume from milliliters to liters using the conversion factor \(1 \text{ L} = 1000 \text{ mL}\).
\( \text{Volume of sample (L)} = 100 \text{ mL} \times \frac{1 \text{ L}}{1000 \text{ mL}} = 0.1 \text{ L} \)
Step 6: Calculate the concentration of Total Volatile Solids in mg/L.
The concentration is calculated by dividing the mass of Volatile Solids (in mg) by the volume of the sample used (in L).
Concentration of Total Volatile Solids (mg/L) = \(\frac{\text{Weight of Volatile Solids (mg)}}{\text{Volume of sample (L)}}\)
\( \text{Concentration} = \frac{13.2 \text{ mg}}{0.1 \text{ L}} = 132 \frac{\text{mg}}{\text{L}} \)
Therefore, the total volatile solids concentration is \(132 \text{ mg/L}\).
| Measurement | Weight (g) |
|---|---|
| Empty Dish | 48.6212 |
| Dish + Dry Solids | 48.6432 |
| Dish + Fixed Solids | 48.6300 |
| Calculated Value | Weight (g) |
|---|---|
| Total Solids | 0.0220 |
| Fixed Solids | 0.0088 |
| Volatile Solids | 0.0132 |
The final calculated value of total volatile solids is 132 mg/L.
Revision Table: Key Solids Analysis Terms
| Term | Description | Measurement Method |
|---|---|---|
| Total Solids (TS) | All matter suspended or dissolved in water or wastewater. | Residue after drying at 103-105 °C. |
| Total Suspended Solids (TSS) | Solids retained by a filter. | Residue on filter paper after drying at 103-105 °C. |
| Total Dissolved Solids (TDS) | Solids that pass through a filter. | Residue in filtrate after drying at 103-105 °C (TS - TSS). |
| Volatile Solids (VS) | Solids lost upon ignition at 550 °C. Represents organic matter. | Weight loss of TS or TSS after heating at 550 °C. |
| Fixed Solids (FS) | Residue remaining after ignition at 550 °C. Represents inorganic matter. | Residue after heating TS or TSS at 550 °C. |
Additional Information on Volatile Solids Analysis
The determination of volatile solids is a crucial parameter in water and wastewater treatment and environmental monitoring. It gives an estimate of the organic content present in the solid fraction. This is important because organic matter can consume dissolved oxygen in water bodies, leading to potential harm to aquatic life. It also indicates the potential for biological decomposition in wastewater treatment processes.
- The standard method for determining volatile solids involves using a muffle furnace at 550 °C. This temperature is chosen to ensure that most organic matter is oxidized or volatilized, while minimizing the decomposition of inorganic salts.
- The accuracy of the measurement depends heavily on precise weighing and careful handling of the sample and dish to avoid contamination or loss of material.
- Results are typically expressed in mg/L for concentration in the original water sample or as a percentage of total solids or total suspended solids.
- High volatile solids often indicate high organic pollution, which requires effective treatment methods like biological processes.
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