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Solid mass by subtraction
The student determined the concentration of sodium chloride in the salt solution. This is the method used.
- Weigh an empty evaporating dish.
- Add 25.0 cm³ of the salt solution into the evaporating dish.
- Heat the evaporating dish and contents.
- Weigh the evaporating dish and contents.
- Repeat steps 3 to 4 until there is no further change in mass.
- Repeat steps 1 to 5 three more times.
How did the student calculate the mass of solid sodium chloride remaining after steps 1 to 5? Tick one box.
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Marking points
- 1 Selects the subtraction of the empty dish mass from the mass of the evaporating dish and dry contents.
Why this answer loses marks
Use the final balance reading as the mass of the solid.
The final reading still includes the evaporating dish, so the container contribution has not been removed.