What is the molar concentration of sodium ions in a 0.350 M Na_3 PO_4 solution?

Question

What is the molar concentration of sodium ions in a 0.350 M Na_3 PO_4 solution? A) 0.117 M B) 9.350 M C) 1.05 M D) 1.40 M a balanced net ionic equation for the reaction of AgNO_3(aq) with KBr(aq). A) AgNO_3 (aq) + KBr(aq) rightarrow AgBr(aq) + KNO_3 (s) B) Ag^+ (aq) + NO_3^-(aq) + K^+(aq) + Br^-(aq) rightarrow Ag^+(aq) + Br^-(aq) + KNO_3(s) C) Ag^+(aq) + NO_3^-(aq) + K^+(aq) + Br^-(aq) rightarrow AgBr(s) + K^+(aq) + NO_3^-(aq) D) Ag^+(aq) + Br^-(aq) rightarrow AgBr(s) Which one of the following compounds is insoluble in water? A) K_2 SO_4 B) NaNO_3 C) PbSO_4 D) Rb_2 CO_3 How many H^+ ions can the acid H_3 PO_4 donate per molecule? A) 0 B) 1 C) 2 D) 3 What is the oxidation number of the chromium atom in Cr_2 O_7^2? A) -2 B) +2 C) +6 D) +7

Explanation / Answer

6. C

Dissociation of Na3PO4 takes place in water as:

Na3PO4 (s) ------> 3Na+(aq) + PO43-(aq)

Thus 1 mole of Na3PO4 produces 3 moles of Na+ and 1 mole of phosphate ion

therefore 0.350 moles of Na3PO4 produces = 0.350*3 3 moles of Na+

Ans = 1.05M (C)

7. C

Each molecule will dissociate into its ions

AgNO3(aq) + KBr(aq)----->AgBr(s) + KNO3 (aq)

Ag+(aq) + NO3- (aq) + K+ (aq) + Br- (aq) --> AgBr(s) +NO3- (aq) + K+ (aq)

8.C

PbSO4 is insoluble in water because Pb2+ and SO42- ions have such a strong attraction towards each other that water molecules fails to pull theses ions apart.

9.D. It can donate 3 H+ ions through ionisation.

10. C +6

Cr2O72-

Let oxidation number of one chromium atom be x

Oxidation number of one oxygen atom is (-2)

Total charge on the molecule =(-2)

Thus

2*x + 7*(-2) = -2

2*x-14 = -2

2*x =14-2

2*x=12

x= 12 / 6

x= +6

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