Question

1)What is the molar concentration of hydoxide ions in a solution made by dissolving 87.4 mg of anhydrous magnesium hydroxide (58.3197 g/mol) in water for a final volume of 3.00 L?

1B)Which of the following is a precipitation reaction?

A) NH4Cl(aq) + KOH(aq) → KCl(aq) + NH3(g) + H2O(l) B) MgSO4(aq) + Ba(NO3)2(aq) → Mg(NO3)2(aq) + BaSO4(s) C) 2 HClO4(aq) + Ca(OH)2(aq) → 2 H2O(l) + Ca(ClO4)2(aq) D) LiCl(aq) + NaNO3(aq) → LiNO3(aq) + NaCl(aq) E) None of the above are precipitation reactions.

1C)Give the complete ionic equation for the reaction (if any) that occurs when aqueous solutions of potassium sulfate and lead (II) nitrate are mixed. A) 2 K+(aq) + S2-(aq) + Pb2+(aq) + 2 NO3-(aq) → PbS(s) + 2 K+(aq) + 2 NO3-(aq) B) 2 K+(aq) + SO42-(aq) + Pb2+(aq) + 2 NO3-(aq) → PbSO4(s) + 2 K+(aq) + 2 NO3-(aq) C) 6 K+(aq) + 3 SO42-(aq) + 3 Pb2+(aq) + 2 N3-(aq) → 3 PbSO4(s) + 6 K+(aq) + 2 N3-(aq) D) 2 K+(aq) + SO42-(aq) + Pb2+(aq) + 2 NO3-(aq) → Pb2+(aq) + SO42-(aq) + 2 KNO3(s) E) No reaction occurs.

Answer 1

1)

mass = 87.4 mg = 0.0874 g

molar mass = 58.3197 g / mol

moles = mass / molar mass = 0.0874 / 58.3197 = 1.50 x 10^-3

molarity = moles / volume = 1.50 x 10^-3 / 3.0 = 5.0 x 10^-4 M

molar concentration of hydoxide ions   = 2 x 5.0 x 10^-4 M

                                                            = 9.99 x 10^-4 M

B) a precipitation reaction always forms solid so

answer : B) MgSO4(aq) + Ba(NO3)2(aq) → Mg(NO3)2(aq) + BaSO4(s)

C) answer :

B) 2 K+(aq) + SO42-(aq) + Pb2+(aq) + 2 NO3-(aq) → PbSO4(s) + 2 K+(aq) + 2 NO3-(aq)