Reading A Solubility Curve Worksheet - Free Printable

Let's solve each question on the Solubility Curve Worksheet using the provided solubility graph.

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1) Define solubility.

Answer:
Solubility is the maximum amount of a substance (solute) that can dissolve in a given amount of solvent (usually water) at a specific temperature to form a saturated solution.

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2) Look at the graph below. In general, how does temperature affect solubility?

Answer:
For most solids, solubility increases with increasing temperature. However, some substances (like Ce₂(SO₄)₃ and CaSO₄) show decreased solubility with increasing temperature.

> *Note:* The trend varies by compound. Most salts like KNO₃, NaNO₃, and KCl increase in solubility as temperature increases, but exceptions exist.

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3) Which compound is LEAST soluble at 10°C?

Answer:
Look at the y-axis value (grams per 100g H₂O) at 10°C for all compounds.

- Ce₂(SO₄)₃ ≈ 5 g/100g H₂O
- KClO₃ ≈ 30 g/100g H₂O
- NH₄Cl ≈ 30 g/100g H₂O
- KCl ≈ 30 g/100g H₂O
- NaCl ≈ 35 g/100g H₂O
- KNO₃ ≈ 20 g/100g H₂O
- NaNO₃ ≈ 80 g/100g H₂O
- KI ≈ 130 g/100g H₂O

✔ Ce₂(SO₄)₃ has the lowest solubility at 10°C (~5 g/100g H₂O).

Answer: Ce₂(SO₄)₃

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4) How many grams of KCl can be dissolved in 100g of water at 80°C?

Answer:
Find the point on the KCl curve at 80°C.

At 80°C, KCl solubility ≈ 50 g / 100g H₂O

Answer: 50 grams

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5) How many grams of NaCl can be dissolved in 100g of water at 90°C?

Answer:
NaCl curve at 90°C: approximately 39 g / 100g H₂O

Answer: 39 grams

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6) At 40°C, how much KNO₃ can be dissolved in 200g of water?

Answer:
First, find solubility of KNO₃ at 40°C: ≈ 60 g / 100g H₂O

So for 200g of water:

$$
\frac{60 \text{ g}}{100 \text{ g H}_2\text{O}} \times 200 = 120 \text{ g}
$$

Answer: 120 grams

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7) Which compound shows the least amount of change in solubility from 0°C–100°C?

Answer:
Compare the change in solubility over 0–100°C:

- NaCl: ~35 g → ~39 g → change = 4 g
- KCl: ~30 g → ~50 g → change = 20 g
- NH₄Cl: ~30 g → ~70 g → change = 40 g
- KNO₃: ~15 g → ~150 g → change = 135 g
- NaNO₃: ~80 g → ~150 g → change = 70 g
- KI: ~130 g → ~150 g → change = 20 g
- KClO₃: ~30 g → ~50 g → change = 20 g
- Ce₂(SO₄)₃: ~5 g → ~5 g → almost no change

But note: Ce₂(SO₄)₃ decreases slightly — from ~5 g to ~5 g (almost flat), but actually it drops a bit.

Wait — let’s look again:

At 0°C: ~5 g
At 100°C: ~5 g → nearly constant

Actually, NaCl changes only from ~35 to ~39 → 4 g

But Ce₂(SO₄)₃ goes from ~5 to ~5 → barely any change.

But NaCl has a very small increase.

Wait — check carefully:

- NaCl: 35 → 39 → +4 g
- Ce₂(SO₄)₃: ~5 → ~5 → essentially unchanged
- But KClO₃: ~30 → ~50 → +20 g
- NH₄Cl: ~30 → ~70 → +40 g

But NaCl and Ce₂(SO₄)₃ both have minimal change.

However, Ce₂(SO₄)₃ is nearly flat and even decreases slightly.

But NaCl has a slight upward trend.

The least change is likely NaCl, because its curve is nearly flat compared to others.

Wait — let’s double-check the graph:

From the graph:
- NaCl: starts at ~35 g at 0°C, ends at ~39 g at 100°C → +4 g
- Ce₂(SO₄)₃: starts at ~5 g, ends at ~5 g → ~0 g change
- But actually, it dips slightly — so maybe Ce₂(SO₄)₃ has no net change.

But NaCl is more stable than others.

Wait — actually, NaCl has one of the flattest curves.

But looking closely, Ce₂(SO₄)₃ is decreasing slightly — so it's not stable.

But NaCl is slightly increasing.

Which has the least change?

Let’s compare:

| Compound | Solubility at 0°C | at 100°C | Change |
|--------|-------------------|----------|--------|
| NaCl | ~35 | ~39 | +4 |
| KCl | ~30 | ~50 | +20 |
| NH₄Cl | ~30 | ~70 | +40 |
| KNO₃ | ~15 | ~150 | +135 |
| NaNO₃ | ~80 | ~150 | +70 |
| KI | ~130 | ~150 | +20 |
| KClO₃ | ~30 | ~50 | +20 |
| Ce₂(SO₄)₃ | ~5 | ~5 | ~0 |

✔ Ce₂(SO₄)₃ has the least change — nearly zero.

But the question says "besides Ce₂(SO₄)₃" in Q14, implying it’s notable.

So probably NaCl is the answer if we exclude Ce₂(SO₄)₃.

But Q7 doesn’t say “besides”, so include all.

Thus, Ce₂(SO₄)₃ shows the least change.

But wait — it actually decreases slightly.

Still, the magnitude of change is minimal.

✔ So Ce₂(SO₄)₃ has the least change.

Answer: Ce₂(SO₄)₃

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8) At 30°C, 90g of NaNO₃ is dissolved in 100g of water. Is this solution saturated or unsaturated?

Answer:
At 30°C, solubility of NaNO₃ ≈ 90 g / 100g H₂O

So 90g dissolved = exactly saturated

Answer: Saturated

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9) At 60°C, 72g of NH₄Cl is dissolved in 100g of water. Is this solution saturated or unsaturated?

Answer:
At 60°C, solubility of NH₄Cl ≈ 55 g / 100g H₂O? Wait — check graph.

At 60°C:

- NH₄Cl curve: around 55–60 g?

Wait — at 50°C: ~50 g
At 70°C: ~65 g
So at 60°C: ≈ 58 g / 100g H₂O

But you're dissolving 72 g, which is more than 58 g

So it exceeds solubility → supersaturated? But usually, we assume it can't dissolve.

So 72 g > 58 g → some will not dissolve → not all dissolves

But the question says “is this solution saturated or unsaturated?”

If 72g is added, but only ~58g can dissolve, then the solution is saturated with undissolved solid.

So the solution (liquid phase) is saturated.

Answer: Saturated

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10) A saturated solution of KClO₃ is formed from 100g of water at 90°C. If cooled to 50°C, how many grams of precipitate are formed?

Answer:
- At 90°C: solubility of KClO₃ ≈ 50 g / 100g H₂O
- At 50°C: solubility ≈ 20 g / 100g H₂O

So when cooled, excess crystals will precipitate:

$$
50 - 20 = 30 \text{ g}
$$

Answer: 30 grams

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11) A saturated solution of NH₄Cl is formed from 100g of water at 80°C. If cooled to 40°C, how many grams of precipitate are formed?

Answer:
- At 80°C: NH₄Cl solubility ≈ 70 g / 100g H₂O
- At 40°C: ≈ 40 g / 100g H₂O

So precipitate = 70 - 40 = 30 g

Answer: 30 grams

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12) Which compounds show a decrease in solubility from 0°C–100°C?

Answer:
Look for curves going downward.

Only Ce₂(SO₄)₃ and Ca(OH)₂ (if present), but here only Ce₂(SO₄)₃ shows decreasing solubility.

Also, NH₃ (ammonia) is gas — but not shown here.

On the graph, Ce₂(SO₄)₃ clearly decreases from 0°C to 100°C.

Is there another?

Check KClO₃? No — it increases.

NH₄Cl? Increases.

Only Ce₂(SO₄)₃ shows decrease.

Answer: Ce₂(SO₄)₃

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13) Which compound is the most soluble at 10°C?

Answer:
At 10°C:

- KI ≈ 130 g
- NaNO₃ ≈ 80 g
- NH₄Cl ≈ 30 g
- KCl ≈ 30 g
- NaCl ≈ 35 g
- KNO₃ ≈ 20 g
- KClO₃ ≈ 30 g
- Ce₂(SO₄)₃ ≈ 5 g

✔ KI is highest at ~130 g

Answer: KI

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14) Which compound (besides Ce₂(SO₄)₃) is the least soluble at 50°C?

Answer:
At 50°C:

- KI ≈ 130
- NaNO₃ ≈ 110
- KNO₃ ≈ 80
- NH₄Cl ≈ 50
- KCl ≈ 40
- NaCl ≈ 37
- KClO₃ ≈ 20
- Ce₂(SO₄)₃ ≈ 5

We want least soluble besides Ce₂(SO₄)₃

So among others: KClO₃ ≈ 20 g → lowest

Others: NaCl ~37, KCl ~40, etc.

✔ KClO₃ is the least soluble (except Ce₂(SO₄)₃)

Answer: KClO₃

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15) For each of the following solutions, explain how much will dissolve and how much remains undissolved.

#### a) 120 g of KCl in 100 g of water at 80°C

- Solubility of KCl at 80°C ≈ 50 g / 100g H₂O
- You add 120 g → only 50 g can dissolve
- Undissolved = 120 - 50 = 70 g

Answer:
50 g will dissolve; 70 g will remain undissolved.

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#### b) 130 g of NaNO₃ in 100 g of water at 50°C

- Solubility of NaNO₃ at 50°C ≈ 110 g / 100g H₂O
- Add 130 g → only 110 g can dissolve
- Undissolved = 130 - 110 = 20 g

Answer:
110 g will dissolve; 20 g will remain undissolved.

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## ✔ Final Answers Summary:

1. Solubility is the maximum amount of solute that can dissolve in a solvent at a given temperature.
2. Temperature generally increases solubility for most solids.
3. Ce₂(SO₄)₃ is least soluble at 10°C.
4. 50 g of KCl in 100g water at 80°C.
5. 39 g of NaCl in 100g water at 90°C.
6. 120 g of KNO₃ in 200g water at 40°C.
7. Ce₂(SO₄)₃ shows least change in solubility (0–100°C).
8. Saturated (90g NaNO₃ at 30°C = exactly solubility).
9. Saturated (72g NH₄Cl > solubility at 60°C).
10. 30 g of KClO₃ precipitate when cooled from 90°C to 50°C.
11. 30 g of NH₄Cl precipitate when cooled from 80°C to 40°C.
12. Ce₂(SO₄)₃ shows decrease in solubility.
13. KI is most soluble at 10°C.
14. KClO₃ is least soluble (besides Ce₂(SO₄)₃) at 50°C.
15a) 50 g dissolves, 70 g undissolved.
15b) 110 g dissolves, 20 g undissolved.

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