1 - University of Illinois at Chicago Department of Chemistry



Any unit that has “ moles” in its definition can be used in stosichiometry. For example, Molarity is a concentration used often in chemistry. Molarity = moles solute / liters of solution. Try these.

1. What is the total molarity of the Cl– ion in a solution formed by mixing together 250.0 mL of 2.0 M AlCl3 with 500.0 mL of 1.00 M MgCl2?

2. The element X is found in the compound X2O7. Identify X if the X-ion has 10 electrons.

3. Potassium hydrogen phthalate, HC8H4O4K (204.233 g/mol) is a primary acidic standard that is used to determine the molarity of a base such as Mg(OH)2.

2 HC8H4O4K (aq) + Mg(OH)2(aq) ( 2 H2O(l) + Mg(C8H4O4K)2 (aq)

In the lab, you weigh out 0.462 g HC8H4O4K, dissolve it in water, and titrate this acid solution with a solution of Mg(OH)2. It requires 56.66 mL of Mg(OH)2 in order to reach the endpoint of the titration. What is the molarity of the Mg(OH)2 solution?

4. Calculate the maximum kJ of heat evolved from a reaction mixture of 25.4 g N2H4 and 95.0 g Cl2 according to the equation,

N2H4(l) + 2 Cl2(g)→ 4 HCl(g) + N2(g) ΔH = -420 kJ/mol

5 A student mixes 25.0 mL of 0.202 M (NH4)3PO4 with 22.6 mL of 0.180 M Ca(NO3)2 according to the following reaction:

2 (NH4)3PO4 (aq) + 3 Ca(NO3)2(aq) ( 6 NH4NO3(?) + Ca3(PO4)2(?)

Calculate the total number of ions in solution when the reaction ends. (find ? first)

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