Multiple Choice
100.0 mL of 0.100 M sodium phosphate is mixed with 100.0 mL of 0.120 M calcium chloride. What mass of calcium phosphate precipitate is formed?
6. Chemical Quantities & Aqueous Reactions
Solution Stoichiometry
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What is the concentration of carbonate ions (CO3^2−) in a 0.090 M carbonic acid (H2CO3) solution, assuming complete dissociation?
A
0.090 M
B
0.045 M
C
0.180 M
D
0.030 M
Verified step by step guidance1
Understand that carbonic acid (H2CO3) is a diprotic acid, meaning it can donate two protons (H+). It dissociates in two steps: first into bicarbonate ions (HCO3^−) and then into carbonate ions (CO3^2−).
Write the dissociation equations for carbonic acid:
1. H2CO3 ⇌ H+ + HCO3^−
2. HCO3^− ⇌ H+ + CO3^2−
Assume complete dissociation of carbonic acid, which means all of the initial H2CO3 will convert to CO3^2− through the two-step dissociation process.
Since the initial concentration of H2CO3 is 0.090 M, and each molecule of H2CO3 ultimately produces one CO3^2− ion, the concentration of CO3^2− will be half of the initial concentration of H2CO3 due to the two-step dissociation.
Calculate the concentration of CO3^2− by dividing the initial concentration of H2CO3 by 2:
[CO3^2−] = 0.090 M / 2
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