A student obtains a 10.0g sample of a white powder labeled as BaCl2. After completely dissolving the powder in 50.0mL of distilled water, the student adds excess Na2SO4(s), which causes a precipitate of BaSO4(s) to form, as represented by the equation above. The student filters the BaSO4(s), rinses it, and dries it until its mass is constant. Which of the following scientific questions could best be answered based on the results of the experiment? Is the Na2SO4(s) used in the experiment pure? A Is the BaCl2(s) used in the experiment pure? B What is the molar solubility of BaCl2 in water? C What is the molar solubility of BaSO4 in water?

The best question is A Is the BaCl2(s) used in the experiment pure?Explanation:

Step 1: Data given

Mass of the BaCl2 sample = 10.0 grams

Volume of water = 50.0 mL

We add excess Na2SO4

A precipitate BaSO4 will be formed

Step 2: The balanced equation

BaCl2(aq) → Ba^2+(aq) + 2Cl-(aq)

Ba^2+(aq) + SO4^2-(aq) →BaSO4(s)

Step 3: Calculate moles BaCl2

Moles BaCl2 = 10.0 grams / 208.23 g/mol

Moles BaCl2 = 0.048 moles

Step 4: Calculate moles Ba^2+

For 1 mol BaCl2 we have 1 mol Ba^2+

For 0.048 moles BaCl2 we have 0.048 moles Ba^2+

Step 5: Calculate mass Ba^2+

Mass Ba^2+ = moles Ba^2+ * molar mass Ba^2+

Mass Ba^2+ = 0.048 moles * 137.33 g/mol

Mass Ba^2+ = 6.59 grams

After measuring the mass of barium in BaSO4 we can determine if the BaCl2 was pure or not.

If the mass = 6.59 grams the BaCl2 was pure

If the mass <6.59 grams the BaCl2 wasn't pure

The best question is A Is the BaCl2(s) used in the experiment pure?

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