---
title: "Solutions and Solubility"
book: "School Chemistry — Grades 1 to 12"
subject: chemistry
language: en
chapter: 9
exercises: 12
source: https://one-course.com/books/chemistry/1/en/chapter/9-solutions-and-solubility
license: CC-BY-NC-SA-4.0
credit: "One Chemistry Book, One Course (one-course.com)"
---

# Chapter 9 — Solutions and Solubility

A bottle of sparkling water is opened: a hiss, and a rush of tiny bubbles rises from nowhere. The water looked perfectly clear a second earlier, yet a gas was dissolved in it all along. Solids [dissolve](https://one-course.com/books/chemistry/1/en/chapter/2-mixing-and-dissolving#def-g2-mixing-and-dissolving-dissolve), liquids [dissolve](https://one-course.com/books/chemistry/1/en/chapter/2-mixing-and-dissolving#def-g2-mixing-and-dissolving-dissolve), and gases [dissolve](https://one-course.com/books/chemistry/1/en/chapter/2-mixing-and-dissolving#def-g2-mixing-and-dissolving-dissolve) too — but never without limit. This chapter names the parts of a solution and measures how much of a substance a liquid can hold.

**You already know.**

A solid that [dissolves](https://one-course.com/books/chemistry/1/en/chapter/2-mixing-and-dissolving#def-g2-mixing-and-dissolving-dissolve) in water disappears from sight and leaves the liquid clear; the clear liquid is a solution, and what was dissolved is still in it ([Chapter 2](https://one-course.com/books/chemistry/1/en/chapter/2-mixing-and-dissolving#ch-g2-mixing-and-dissolving)). A solution is a [homogeneous mixture](https://one-course.com/books/chemistry/1/en/chapter/8-pure-substances-and-mixtures#def-g6-pure-substances-and-mixtures-homogeneous) of [chemical species](https://one-course.com/books/chemistry/1/en/chapter/8-pure-substances-and-mixtures#def-g6-pure-substances-and-mixtures-species) ([Chapter 8](https://one-course.com/books/chemistry/1/en/chapter/8-pure-substances-and-mixtures#ch-g6-pure-substances-and-mixtures)). [Evaporating](https://one-course.com/books/chemistry/1/en/chapter/3-separating-mixtures#def-g3-separating-mixtures-evaporate) the water gets the dissolved solid back ([Chapter 3](https://one-course.com/books/chemistry/1/en/chapter/3-separating-mixtures#ch-g3-separating-mixtures)).

![Opening a bottle of sparkling water: the dissolved gas comes out as bubbles.](https://one-course.com/images/onecourse/chapters/chemistry-1/g6-solutions-and-solubility/img-496ac65c5d6a.jpg)

*Opening a bottle of sparkling water: the dissolved gas comes out as bubbles.*

## 9.1 Solute and solvent

**Definition 9.1 (Solute, solvent, aqueous solution).**

In a solution, the substance that [dissolves](https://one-course.com/books/chemistry/1/en/chapter/2-mixing-and-dissolving#def-g2-mixing-and-dissolving-dissolve) is the *solute*, and the liquid it [dissolves](https://one-course.com/books/chemistry/1/en/chapter/2-mixing-and-dissolving#def-g2-mixing-and-dissolving-dissolve) in is the *solvent*. When the solvent is water, the solution is an *aqueous solution*.

**Example 9.2 (Solvents other than water).**

Water is the commonest [solvent](#def-g6-solutions-and-solubility-solute), but not the only one. Nail varnish does not [dissolve](https://one-course.com/books/chemistry/1/en/chapter/2-mixing-and-dissolving#def-g2-mixing-and-dissolving-dissolve) in water; it [dissolves](https://one-course.com/books/chemistry/1/en/chapter/2-mixing-and-dissolving#def-g2-mixing-and-dissolving-dissolve) in propanone (acetone), the [solvent](#def-g6-solutions-and-solubility-solute) of nail-varnish remover. Grease and oil paint [dissolve](https://one-course.com/books/chemistry/1/en/chapter/2-mixing-and-dissolving#def-g2-mixing-and-dissolving-dissolve) in white spirit. Many medicines are dissolved in ethanol. A solution can have several [solutes](#def-g6-solutions-and-solubility-solute): sea water holds dissolved salt and many other substances.

**Safety.**

![](https://one-course.com/images/onecourse/chapters/chemistry-1/g6-solutions-and-solubility/fig-7323bebe7717.svg)

![](https://one-course.com/images/onecourse/chapters/chemistry-1/g6-solutions-and-solubility/fig-895ed5895dff.svg)

Propanone (acetone): highly flammable liquid and vapour (GHS02); it irritates the eyes and its vapour can make one drowsy or dizzy (GHS07). It is used in a ventilated room, far from any flame.

**Proposition 9.3 (The masses add up).**

The mass of a solution is the mass of the [solvent](#def-g6-solutions-and-solubility-solute) plus the mass of the dissolved [solute](#def-g6-solutions-and-solubility-solute): nothing is lost when a solid [dissolves](https://one-course.com/books/chemistry/1/en/chapter/2-mixing-and-dissolving#def-g2-mixing-and-dissolving-dissolve), even though it can no longer be seen.

![Dissolving 10\, g of sugar in 100\, g of water gives 110\, g of solution (the mass of the beaker is left out).](https://one-course.com/images/onecourse/chapters/chemistry-1/g6-solutions-and-solubility/fig-78b8bb51a9da.svg)

*Dissolving $10\,\mathrm{g}$ of sugar in $100\,\mathrm{g}$ of water gives $110\,\mathrm{g}$ of solution (the mass of the beaker is left out).*

## 9.2 Saturation and solubility

**Definition 9.4 (Saturated solution).**

A solution is a *saturated solution* when it cannot [dissolve](https://one-course.com/books/chemistry/1/en/chapter/2-mixing-and-dissolving#def-g2-mixing-and-dissolving-dissolve) any more of its [solute](#def-g6-solutions-and-solubility-solute): any [solute](#def-g6-solutions-and-solubility-solute) added stays at the bottom, undissolved, however long we stir.

**Definition 9.5 (Solubility).**

The *solubility* of a [solute](#def-g6-solutions-and-solubility-solute) in a [solvent](#def-g6-solutions-and-solubility-solute) is the largest mass of [solute](#def-g6-solutions-and-solubility-solute) that a given amount of [solvent](#def-g6-solutions-and-solubility-solute) can [dissolve](https://one-course.com/books/chemistry/1/en/chapter/2-mixing-and-dissolving#def-g2-mixing-and-dissolving-dissolve), at a given temperature. For a solid in water it is often given in grams per litre (or per kilogram) of water.

**Proposition 9.6 (Some solubilities in water).**

Measured solubilities in water differ enormously:

| [solute](#def-g6-solutions-and-solubility-solute) | [solubility](#def-g6-solutions-and-solubility-solubility) in water | conditions |
| --- | --- | --- |
| sugar (sucrose) | about $2000\,\mathrm{g}$ per litre of water | room temperature |
| salt (sodium chloride) | $360\,\mathrm{g}$ per kilogram of water | $25\,{}^{\circ}\mathrm{C}$ |
| carbon dioxide | about $1.5\,\mathrm{g}$ per litre | $25\,{}^{\circ}\mathrm{C}$, under the gas |
| oxygen | about $0.04\,\mathrm{g}$ per litre | $20\,{}^{\circ}\mathrm{C}$, under the gas |
| sand, chalk | practically none | — |

A litre of water can [dissolve](https://one-course.com/books/chemistry/1/en/chapter/2-mixing-and-dissolving#def-g2-mixing-and-dissolving-dissolve) more than its own mass of sugar, but not even half a gram of oxygen.

**Method 9.7 (Will it all dissolve?).**

To know whether a mass $m$ of [solute](#def-g6-solutions-and-solubility-solute) [dissolves](https://one-course.com/books/chemistry/1/en/chapter/2-mixing-and-dissolving#def-g2-mixing-and-dissolving-dissolve) completely in a volume of water:

1. find the [solubility](#def-g6-solutions-and-solubility-solubility) of the [solute](#def-g6-solutions-and-solubility-solute) (in g per litre of water);
2. compute the largest mass that this volume of water can [dissolve](https://one-course.com/books/chemistry/1/en/chapter/2-mixing-and-dissolving#def-g2-mixing-and-dissolving-dissolve) ;
3. compare with $m$ : if $m$ is smaller, everything [dissolves](https://one-course.com/books/chemistry/1/en/chapter/2-mixing-and-dissolving#def-g2-mixing-and-dissolving-dissolve) ; if $m$ is larger, the solution is saturated and the rest stays at the bottom.

**Example 9.8 (Salt in a glass).**

Can $50\,\mathrm{g}$ of salt [dissolve](https://one-course.com/books/chemistry/1/en/chapter/2-mixing-and-dissolving#def-g2-mixing-and-dissolving-dissolve) in $200\,\mathrm{mL}$ of water (about $200\,\mathrm{g}$)? One kilogram of water [dissolves](https://one-course.com/books/chemistry/1/en/chapter/2-mixing-and-dissolving#def-g2-mixing-and-dissolving-dissolve) at most $360\,\mathrm{g}$ of salt, so $200\,\mathrm{g}$ of water [dissolves](https://one-course.com/books/chemistry/1/en/chapter/2-mixing-and-dissolving#def-g2-mixing-and-dissolving-dissolve) at most $360 \times
\frac{200}{1000} = 72\,\mathrm{g}$. Since $50 < 72$, all the salt [dissolves](https://one-course.com/books/chemistry/1/en/chapter/2-mixing-and-dissolving#def-g2-mixing-and-dissolving-dissolve).

![Adding more and more salt to the same water. Once the solution is saturated, extra salt stays at the bottom.](https://one-course.com/images/onecourse/chapters/chemistry-1/g6-solutions-and-solubility/fig-3fd23b07052f.svg)

*Adding more and more salt to the same water. Once the solution is saturated, extra salt stays at the bottom.*

**In the lab — Saturating salt water.**

The teacher adds salt to $100\,\mathrm{mL}$ of water one spoonful at a time, stirring well after each. The first spoonfuls disappear; then a spoonful no longer [dissolves](https://one-course.com/books/chemistry/1/en/chapter/2-mixing-and-dissolving#def-g2-mixing-and-dissolving-dissolve) completely and white grains stay at the bottom: the solution is saturated. Weighing the salt used shows that about $36\,\mathrm{g}$ have dissolved.

## 9.3 Miscible and immiscible liquids

**Definition 9.9 (Miscible and immiscible liquids).**

Two liquids are *miscible* when, mixed together, they give one single homogeneous liquid. They are *immiscible* when they separate into two layers, the lighter one on top.

**Example 9.10 (Water with ethanol, water with oil).**

Water and ethanol are [miscible](#def-g6-solutions-and-solubility-miscible): shaken together, they give one clear liquid. Water and oil are [immiscible](#def-g6-solutions-and-solubility-miscible): however hard they are shaken, the oil comes back up and floats on the water in a separate layer. In a jar of salad dressing the oil floats above the vinegar, which is mostly water.

![Miscible liquids give one layer; immiscible liquids give two.](https://one-course.com/images/onecourse/chapters/chemistry-1/g6-solutions-and-solubility/fig-bf173fd6db1d.svg)

*[Miscible](#def-g6-solutions-and-solubility-miscible) liquids give one layer; [immiscible](#def-g6-solutions-and-solubility-miscible) liquids give two.*

![Salad dressing: oil and vinegar are immiscible.](https://one-course.com/images/onecourse/chapters/chemistry-1/g6-solutions-and-solubility/img-ebabe2cd570f.jpg)

*Salad dressing: oil and vinegar are [immiscible](#def-g6-solutions-and-solubility-miscible).*

## 9.4 Gases dissolve too

**Proposition 9.11 (Dissolved gases).**

Gases [dissolve](https://one-course.com/books/chemistry/1/en/chapter/2-mixing-and-dissolving#def-g2-mixing-and-dissolving-dissolve) in water, a little. Sparkling drinks are made by dissolving carbon dioxide in them under pressure in a closed bottle; when the bottle is opened, part of the gas comes back out as bubbles. Water in contact with [air](https://one-course.com/books/chemistry/1/en/chapter/4-air-a-mixture-of-gases#def-g4-air-a-mixture-of-gases-air) holds some dissolved oxygen, which fish take in through their gills. A gas [dissolves](https://one-course.com/books/chemistry/1/en/chapter/2-mixing-and-dissolving#def-g2-mixing-and-dissolving-dissolve) less in warm water than in cold water: a warm sparkling drink goes flat faster.

**Example 9.12 (Oceans and carbon dioxide).**

The oceans are in contact with the [air](https://one-course.com/books/chemistry/1/en/chapter/4-air-a-mixture-of-gases#def-g4-air-a-mixture-of-gases-air) over two thirds of the Earth’s surface. Carbon dioxide of the [air](https://one-course.com/books/chemistry/1/en/chapter/4-air-a-mixture-of-gases#def-g4-air-a-mixture-of-gases-air) [dissolves](https://one-course.com/books/chemistry/1/en/chapter/2-mixing-and-dissolving#def-g2-mixing-and-dissolving-dissolve) in them, so the oceans take up part of the carbon dioxide that people release into the [air](https://one-course.com/books/chemistry/1/en/chapter/4-air-a-mixture-of-gases#def-g4-air-a-mixture-of-gases-air).

![An aquarium: the air bubbles keep the water supplied with dissolved oxygen for the fish.](https://one-course.com/images/onecourse/chapters/chemistry-1/g6-solutions-and-solubility/img-213f04b33c58.jpg)

*An aquarium: the [air](https://one-course.com/books/chemistry/1/en/chapter/4-air-a-mixture-of-gases#def-g4-air-a-mixture-of-gases-air) bubbles keep the water supplied with dissolved oxygen for the fish.*

## 9.5 Exercises

**Exercise 9.1 ★.**

In sugar water, name the [solute](#def-g6-solutions-and-solubility-solute) and the [solvent](#def-g6-solutions-and-solubility-solute). Is it an [aqueous solution](#def-g6-solutions-and-solubility-solute)?

**Solution of Exercise 9.1.**

[Solute](#def-g6-solutions-and-solubility-solute): sugar. [Solvent](#def-g6-solutions-and-solubility-solute): water. Yes, the [solvent](#def-g6-solutions-and-solubility-solute) is water: it is an [aqueous solution](#def-g6-solutions-and-solubility-solute).

**Exercise 9.2 ★.**

What is a [saturated solution](#def-g6-solutions-and-solubility-saturated)? How can you see that a solution is saturated?

**Solution of Exercise 9.2.**

A solution that cannot [dissolve](https://one-course.com/books/chemistry/1/en/chapter/2-mixing-and-dissolving#def-g2-mixing-and-dissolving-dissolve) any more of its [solute](#def-g6-solutions-and-solubility-solute). [Solute](#def-g6-solutions-and-solubility-solute) added to it stays undissolved at the bottom.

**Exercise 9.3 ★.**

$20\,\mathrm{g}$ of salt are dissolved in $250\,\mathrm{g}$ of water. What is the mass of the solution?

**Solution of Exercise 9.3.**

$250 + 20 = 270\,\mathrm{g}$.

**Exercise 9.4 ★.**

[Miscible](#def-g6-solutions-and-solubility-miscible) or [immiscible](#def-g6-solutions-and-solubility-miscible) with water: ethanol, cooking oil, vinegar?

**Solution of Exercise 9.4.**

Ethanol: [miscible](#def-g6-solutions-and-solubility-miscible). Cooking oil: [immiscible](#def-g6-solutions-and-solubility-miscible). Vinegar: [miscible](#def-g6-solutions-and-solubility-miscible) (it is mostly water).

**Exercise 9.5 ★.**

Name the [solvent](#def-g6-solutions-and-solubility-solute) of nail-varnish remover and give the meaning of its two pictograms.

**Solution of Exercise 9.5.**

Propanone (acetone). GHS02: highly flammable; GHS07: irritates the eyes, the vapour can cause drowsiness or dizziness.

**Exercise 9.6 ★★.**

Using the [solubility](#def-g6-solutions-and-solubility-solubility) of salt, find the largest mass of salt that $500\,\mathrm{g}$ of water can [dissolve](https://one-course.com/books/chemistry/1/en/chapter/2-mixing-and-dissolving#def-g2-mixing-and-dissolving-dissolve) at $25\,{}^{\circ}\mathrm{C}$.

**Solution of Exercise 9.6.**

$360 \times \frac{500}{1000} = 180\,\mathrm{g}$.

**Exercise 9.7 ★★.**

$80\,\mathrm{g}$ of salt are stirred into $200\,\mathrm{g}$ of water at $25\,{}^{\circ}\mathrm{C}$. Does it all [dissolve](https://one-course.com/books/chemistry/1/en/chapter/2-mixing-and-dissolving#def-g2-mixing-and-dissolving-dissolve)? If not, what mass stays at the bottom?

**Solution of Exercise 9.7.**

$200\,\mathrm{g}$ of water [dissolve](https://one-course.com/books/chemistry/1/en/chapter/2-mixing-and-dissolving#def-g2-mixing-and-dissolving-dissolve) at most $360 \times \frac{200}{1000} =
72\,\mathrm{g}$. No: $80 - 72 = 8\,\mathrm{g}$ stay at the bottom.

**Exercise 9.8 ★★.**

$25\,\mathrm{g}$ of sugar are dissolved in $225\,\mathrm{g}$ of water. What percentage of the mass of the solution is sugar?

**Solution of Exercise 9.8.**

The solution weighs $225 + 25 = 250\,\mathrm{g}$; $\frac{25}{250} =
10\,\%$.

**Exercise 9.9 ★★.**

Look at the figure of the three beakers of salt water. In which beaker could more salt still [dissolve](https://one-course.com/books/chemistry/1/en/chapter/2-mixing-and-dissolving#def-g2-mixing-and-dissolving-dissolve)?

**Solution of Exercise 9.9.**

In the first beaker, where all the salt has dissolved and the solution is not yet saturated.

**Exercise 9.10 ★★.**

Why does a bottle of sparkling water fizz when it is opened, and not before?

**Solution of Exercise 9.10.**

The carbon dioxide was dissolved under pressure in the closed bottle. Opening it lowers the pressure: the water can hold less gas, and the extra gas comes out as bubbles.

**Exercise 9.11 ★★★.**

A litre of water can [dissolve](https://one-course.com/books/chemistry/1/en/chapter/2-mixing-and-dissolving#def-g2-mixing-and-dissolving-dissolve) about $2000\,\mathrm{g}$ of sugar but only about $0.04\,\mathrm{g}$ of oxygen. How many times more sugar than oxygen is that?

**Solution of Exercise 9.11.**

$2000 \div 0.04 = 50\,000$ times more.

**Exercise 9.12 ★★★.**

In summer, the water of a pond warms up and fish come up to the surface to gulp [air](https://one-course.com/books/chemistry/1/en/chapter/4-air-a-mixture-of-gases#def-g4-air-a-mixture-of-gases-air). Use this chapter to explain why.

**Solution of Exercise 9.12.**

A gas [dissolves](https://one-course.com/books/chemistry/1/en/chapter/2-mixing-and-dissolving#def-g2-mixing-and-dissolving-dissolve) less in warm water: the warm pond holds less dissolved oxygen, and the fish lack oxygen.

## 9.6 Problem: The Cheese-Maker’s Brine

**Problem 9.1.**

Weekend problem — a bath of saturated salt water for cheeses, and what the summer heat does to it

Many cheeses are soaked for a few hours in a bath of brine: water saturated with salt. A cheese-maker fills a tank with $20\,\mathrm{L}$ of water ($20\,\mathrm{kg}$) and adds salt until some stays undissolved at the bottom. Take the [solubility](#def-g6-solutions-and-solubility-solubility) of salt as $360\,\mathrm{g}$ per kilogram of water.

**Part I — Words.**

1. In the brine, which is the [solute](#def-g6-solutions-and-solubility-solute) and which the [solvent](#def-g6-solutions-and-solubility-solute) ?
2. What does “saturated” mean for the brine?
3. Why does the cheese-maker add salt until a little stays at the bottom?

**Part II — Making the brine.**

4. What mass of salt [dissolves](https://one-course.com/books/chemistry/1/en/chapter/2-mixing-and-dissolving#def-g2-mixing-and-dissolving-dissolve) in the $20\,\mathrm{kg}$ of water?
5. What is the mass of the brine (without the undissolved salt)?
6. What percentage of the mass of the brine is salt? Round to the nearest whole number.
7. One day only $5\,\mathrm{kg}$ of salt are added. Is the brine saturated? How much more salt could it [dissolve](https://one-course.com/books/chemistry/1/en/chapter/2-mixing-and-dissolving#def-g2-mixing-and-dissolving-dissolve) ?

**Part III — A hot summer.** During a hot week, $5\,\mathrm{L}$ ($5\,\mathrm{kg}$) of water evaporate from the saturated brine of Part II, and no salt is lost.

8. How much water is left in the tank?
9. What mass of salt can this water still hold dissolved?
10. What happens to the salt that the remaining water cannot hold?
11. How can the cheese-maker see, by looking, that this has happened?
12. Compute the mass of salt that has crystallised at the bottom of the tank.

**Solution of Problem 9.1.**

**1.** [Solute](#def-g6-solutions-and-solubility-solute): salt. [Solvent](#def-g6-solutions-and-solubility-solute): water.

**2.** The water holds as much salt as it can: no more salt can [dissolve](https://one-course.com/books/chemistry/1/en/chapter/2-mixing-and-dissolving#def-g2-mixing-and-dissolving-dissolve) in it.

**3.** The undissolved salt at the bottom proves that the brine is saturated: it holds as much salt as possible.

**4.** $360 \times 20 = 7200\,\mathrm{g} = 7.2\,\mathrm{kg}$.

**5.** $20 + 7.2 = 27.2\,\mathrm{kg}$.

**6.** $\frac{7.2}{27.2} \approx 0.26$: about $26\,\%$.

**7.** No: the water could [dissolve](https://one-course.com/books/chemistry/1/en/chapter/2-mixing-and-dissolving#def-g2-mixing-and-dissolving-dissolve) $7.2\,\mathrm{kg}$. It could still [dissolve](https://one-course.com/books/chemistry/1/en/chapter/2-mixing-and-dissolving#def-g2-mixing-and-dissolving-dissolve) $7.2 - 5 = 2.2\,\mathrm{kg}$.

**8.** $20 - 5 = 15\,\mathrm{kg}$ of water ($15\,\mathrm{L}$).

**9.** $360 \times 15 = 5400\,\mathrm{g} = 5.4\,\mathrm{kg}$.

**10.** It comes out of solution as solid crystals: it crystallises and sinks to the bottom.

**11.** New white crystals appear and pile up at the bottom of the tank.

**12.** $7.2 - 5.4 = 1.8\,\mathrm{kg}$ of salt have crystallised.