Model 1 - Ion Concentrations for Acids and Bases, illustrating the relationship between hydronium and hydroxide ion concentrations in different solutions.

Let’s go step by step to understand and solve the questions based on Model 1.

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Question 1: What does the symbol [H₃O⁺] in Model 1 indicate?

In chemistry, when we write something like [H₃O⁺], the square brackets mean “concentration of.” So [H₃O⁺] means the concentration (how much there is) of hydronium ions in the solution. Hydronium ions are what make a solution acidic — they form when acids dissolve in water.

✔ Final Answer for Q1: The molar concentration of hydronium ion.

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Question 2: In Beaker 2, which ion has a higher concentration, hydronium ion or hydroxide ion?

Look at Beaker 2 in the table:

- [H₃O⁺] = 1.0 × 10⁻³ M
- [OH⁻] = 1.0 × 10⁻¹¹ M

Which number is bigger? Remember: with negative exponents, the smaller the exponent (closer to zero), the larger the number.

So 10⁻³ is way bigger than 10⁻¹¹.

That means hydronium ion concentration is much higher.

✔ Final Answer for Q2: Hydronium ion.

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Question 3: Describe how the concentration of hydronium ion was calculated for Beaker 3 in Model 1 from the concentration of the acid.

Beaker 3 contains 0.000010 M HCl(aq). That’s the same as 1.0 × 10⁻⁵ M.

HCl is a strong acid — that means it breaks apart completely in water:

HCl → H⁺ + Cl⁻
But H⁺ immediately joins with water to become H₃O⁺.

So every molecule of HCl gives one H₃O⁺ ion.

Therefore, if you start with 1.0 × 10⁻⁵ M HCl, you end up with 1.0 × 10⁻⁵ M H₃O⁺.

✔ Final Answer for Q3: Since HCl is a strong acid, all of the molecules ionize in water. Therefore, the H₃O⁺ concentration is equal to the initial acid concentration in the solution.

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Question 4: Describe how the concentration of hydroxide ion was calculated for Beaker 8 in Model 1 from the concentration of the base.

Beaker 8 contains 0.00010 M NaOH(aq) = 1.0 × 10⁻⁴ M.

NaOH is a strong base — it breaks apart completely in water:

NaOH → Na⁺ + OH⁻

So every molecule of NaOH gives one OH⁻ ion.

Therefore, if you start with 1.0 × 10⁻⁴ M NaOH, you get 1.0 × 10⁻⁴ M OH⁻.

Wait — but in the table, for Beaker 8, [OH⁻] is listed as 1.0 × 10⁻⁴ M — yes, that matches!

Also note: even though [H₃O⁺] is very small (1.0 × 10⁻¹⁰ M), that’s because in any aqueous solution, [H₃O⁺] × [OH⁻] = 1 × 10⁻¹⁴ (this is called the ion product of water). But the question only asks how [OH⁻] was found from the base — so we don’t need to use that here.

✔ Final Answer for Q4: Since NaOH is a strong base, it completely dissociates in water. Therefore, the OH⁻ concentration is equal to the initial base concentration in the solution.

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Final Answer:
1. The molar concentration of hydronium ion.
2. Hydronium ion.
3. Since HCl is a strong acid, all of the molecules ionize in water. Therefore, the H₃O⁺ concentration is equal to the initial acid concentration in the solution.
4. Since NaOH is a strong base, it completely dissociates in water. Therefore, the OH⁻ concentration is equal to the initial base concentration in the solution.