Where are the substances?
Answer:

Explanation:
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In this case, since the normal boiling point of X is 117.80 °C, the boiling point elevation constant is 1.48 °C*kg*mol⁻¹, the mass of X is 100 g and the boiling point of the mixture of X and KBr boils at 119.3 °C, we can use the following formula:

Whereas the Van't Hoff factor of KBr is 2 as it dissociates into potassium cations and bromide ions; it means that we can compute the molality of the solution:

Next, given the mass of solventin kg (0.1 kg from 100 g), we compute the moles KBr:

Finally, considering the molar mass of KBr (119 g/mol) we compute the mass that was dissolved:

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Answer:
a) 0.100 M
b) 0.395 M
Explanation:
a) Calculate the molarity of a solution that contains 0.200 moles of NaOH (solute) in 2.00 L of solution
We will use the following expression for molarity.
[NaOH] = moles of solute / liters of solution
[NaOH] = 0.200 mol/2.00 L = 0.100 M
b) Calculate the molarity for a solution that contains 15.5 g of NaCl (solute, 58.44 g/mol) in 671 mL of solution
We will use the following expression for molarity.
[NaCl] = mass of solute / molar mass of solute × liters of solution
[NaCl] = 15.5 g / 58.44 g/mol × 0.671 L = 0.395 M
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