Multiple Choice
A 0.846-g sample containing barium ions is completely dissolved in water and treated with excess Na2SO4. 0.746 g of BaSO4 precipitates. What is the mass percent of barium in the sample?
3. Chemical Reactions
Stoichiometry
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A mixture of NaCl and NaBr has a mass of 2.01 g and is found to contain 0.77 g of Na. What is the mass of NaBr in the mixture?
A
0.77 g
B
0.50 g
C
1.24 g
D
1.01 g
Verified step by step guidance1
First, identify the components of the mixture: NaCl and NaBr. Both contain sodium (Na), and the total mass of sodium in the mixture is given as 0.77 g.
Calculate the molar mass of NaCl and NaBr. The molar mass of NaCl is approximately 58.44 g/mol, and the molar mass of NaBr is approximately 102.89 g/mol.
Determine the mass of sodium in each compound. The molar mass of sodium (Na) is approximately 22.99 g/mol. Calculate the percentage of sodium in NaCl and NaBr using the formula: \( \text{Percentage of Na} = \frac{\text{Molar mass of Na}}{\text{Molar mass of compound}} \times 100 \).
Set up an equation using the mass of sodium in the mixture. Let \( x \) be the mass of NaCl and \( y \) be the mass of NaBr. The equation for sodium mass is: \( 0.77 = \frac{22.99}{58.44}x + \frac{22.99}{102.89}y \).
Solve the system of equations: \( x + y = 2.01 \) (total mass of the mixture) and the sodium mass equation to find the values of \( x \) and \( y \). The value of \( y \) will give you the mass of NaBr in the mixture.
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