Q: Which formula is used to calculate osmolarity directly from molarity?

$$\mathrm{Osmolarity} = \mathrm{Molarity} \times \text{number of ions per formula unit}$$

Question 1

Which of the following best describes osmolarity?

Accepted Answer

The number of moles of ions per liter of solution.

Question 2

A solution is prepared by dissolving 5.1 g of $$\mathrm{$$AlCl_3$$} in $$enough water to make 500 mL of solution. What is the osmolarity of chloride ions in the solution? (Molar mass of $$\mathrm{$$AlCl_3$$} = 133.5 g/$$mol)

Accepted Answer

$$0.383\ \mathrm{osmoles/L}$$

Question 3

Which formula is used to calculate osmolarity directly from molarity?

Accepted Answer

$$\mathrm{Osmolarity} = \mathrm{Molarity} 	imes 	ext{number of ions per formula unit}$$

Question 4

What is the concentration of hydroxide ions in a $$0.350\ \mathrm{M}$$ solution of gallium hydroxide, $$\mathrm{Ga(OH)_3}$$?

Accepted Answer

$$1.05\ \mathrm{M}$$

Question 5

How many moles of $$\mathrm{Ca$$^{2+}$$}$$ ions are in $$8.76\ \mathrm{L} of$$ $$0.421\ \mathrm{M}$$ $$\mathrm{Ca($$ClO_4$$)_2}$$ solution?

Accepted Answer

$$3.69\ \mathrm{mol}$$

Question 6

Which of the following solutions will have the highest concentration of bromide ions?

Accepted Answer

$$0.10\ \mathrm{M}\ \mathrm{$$CaBr_2$$}$$

Question 7

How many milligrams of nitrate ions are required to prepare $$820\ \mathrm{mL} of$$ $$0.330\ \mathrm{M}\ \mathrm{Ba(NO_3$)_2}$$ solution? (Molar mass of $$\mathrm{NO_3$^-}$$ = $$62.0\ \mathrm{g/mol})$$

Accepted Answer

$$33,540\ \mathrm{mg}$$

Question 8

How many bromide ions are present in $$65.5\ \mathrm{mL} of$$ $$0.210\ \mathrm{M}\ \mathrm{$$GaBr_3$$}$$ solution?

Accepted Answer

$$7.75 	imes 10$$^{22}$$ ions

Question 9

A hospital needs to prepare $$1.00\ \mathrm{L} of$$ $$0.250\ \mathrm{M}\ \mathrm{Na_2SO_4}$$ solution. How many moles of sodium ions will be present in the final solution?

Accepted Answer

$$0.500\ \mathrm{mol}$$

Question 10

If $$0.500\ \mathrm{mol} of$$ $$\mathrm{$$MgCl_2$$} is $$dissolved in enough water to make $$2.00\ \mathrm{L} of $$solution, what is the osmolarity of the solution?

Accepted Answer

$$0.750\ \mathrm{osmoles/L}$$

Question 11

Which of the following best explains why $$\mathrm{$$CaCl_2$$}$$ produces more ions in solution than $$\mathrm{NaCl} at $$the same molarity?

Accepted Answer

$$\mathrm{$$CaCl_2$$}$$ dissociates into three ions per formula unit, while $$\mathrm{NaCl}$$ dissociates into two.

Question 12

A solution contains $$0.200\ \mathrm{mol} of$$ $$\mathrm{K_2SO_4} in$$ $$1.00\ \mathrm{L} of $$water. What is the osmolarity of the solution?

Accepted Answer

$$0.600\ \mathrm{osmoles/L}$$

Osmolarity: Concepts, Calculations, and Applications

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