Quantitative chemistry — AQA GCSE Practice Question 01.4

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The question asks how to find the mass of *only* the solid sodium chloride. 1. Identify the measurement that gives the mass of the container + salt (this is the final mass). 2. Identify the measurement that gives the mass of the container alone (this is the initial mass). 3. To find the mass of the salt, you must subtract the mass of the container from the combined mass of the container and salt.

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D.Mass of evaporating dish and dry contents – mass of empty evaporating dish✓ Correct

To find the mass of a substance in a container, you must use the principle of "weighing by difference". 1. First, the mass of the empty container is measured (mass of empty evaporating dish). 2. After the process (in this case, adding the solution and evaporating the water), the mass of the container with the substance inside is measured (mass of evaporating dish and dry contents). 3. Subtracting the initial mass from the final mass removes the mass of the container, leaving only the mass of the substance. Therefore, Mass of salt = (Mass of dish + salt) - (Mass of dish).

Common mistakes

✗ Selecting an option that adds masses instead of subtracting. ✗ Confusing the mass of the salt solution with the mass of the dry salt.

How did the student calculate the mass of solid sodium chloride remaining after steps 1 to 5?

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