E2.4 Investigate qualitative and quantitative solution properties

Ontario Grade 11 Chemistry

Solutions and Solubility

Ontario Grade 11 Chemistry — E2.4

A spoonful of salt can disappear in water, leaving a clear liquid. The salt has not vanished: its particles have spread through the water. You can describe what you observe, such as whether the mixture is clear or whether solid remains. You can also measure a property, such as the amount of dissolved substance in a given volume. These are qualitative and quantitative ways to investigate solutions.

What you will learn

Describe observable properties that help identify and compare solutions.
Explain how solute and solvent particles form a solution.
Distinguish unsaturated, saturated, and supersaturated solutions using evidence.
Calculate the molar concentration of a solution and report units correctly.
Plan a fair investigation that collects qualitative and quantitative evidence.

1. From mixtures to solutions

A mixture contains two or more substances together. Some mixtures look uniform throughout. A solution is a uniform mixture in which one or more substances are spread among another substance's particles. Uniform means that a small sample from one part has the same composition as a sample from another part.

The substance that dissolves is the solute. The substance that does the dissolving is the solvent. In salt water, salt is the solute and water is the solvent. When a solid dissolves, its particles separate from the solid and spread among the solvent particles. The particles are still present, even if they are too small to see.

A solution is one kind of homogeneous mixture. Homogeneous means uniform throughout. A mixture with visible pieces or layers is not uniform, so it is not a single solution. A clear appearance can be evidence of uniformity, but appearance alone does not prove what substances are present.

A solution contains solute and solvent.
Dissolving spreads solute particles through the solvent; it does not make the particles disappear.
Observations describe what is seen. They do not identify every particle in a sample.

2. Qualitative evidence and solubility

Qualitative evidence describes a property without giving a numerical measurement. Useful observations include whether a mixture is clear or cloudy, whether solid remains at the bottom, and whether two liquid layers form. Record what you actually observe rather than guessing at a cause.

Solubility is the greatest amount of a solute that can dissolve in a stated amount of solvent under stated conditions. Temperature matters, so a solubility comparison must use the same temperature. A solute may dissolve readily in one solvent but not in another.

An unsaturated solution can dissolve more solute under the stated conditions. A saturated solution contains as much dissolved solute as it can under those conditions. If more solid is added to a saturated solution, some may remain undissolved. The solid left over is evidence that the solution may be saturated, provided it has had time to mix and the conditions have not changed.

A supersaturated solution contains more dissolved solute than a saturated solution normally holds under the stated conditions. It is unstable: some excess solute can form solid if the solution is disturbed or a small crystal is added. Do not identify a solution as supersaturated from appearance alone; you need evidence that it contains more dissolved solute than the saturation amount.

A fair investigation changes one factor at a time, such as the mass of solute added, while keeping the solvent amount and temperature the same. Use a balance to measure mass and a suitable measuring tool for volume. Record the conditions and observations. Do not treat a suggested procedure as completed experimental evidence.

Qualitative evidence includes visible clarity, layers, and undissolved solid.
Solubility comparisons require stated conditions, especially temperature and solvent amount.
Unsaturated, saturated, and supersaturated describe how much solute is dissolved relative to the limit.

3. Quantitative solution properties

Quantitative evidence uses numbers and units. A common solution measurement is molar concentration, often called concentration in this course. It tells how many moles of solute are present in each litre of solution. A mole is a chemistry counting unit. Concentration is written with the symbol

c

and commonly has units of moles per litre,

ext{mol/L}

.

To use this relationship, the amount of solute must be in moles and the volume must be the volume of the whole solution in litres. If a problem gives mass instead, first convert mass to amount using the molar mass. Molar mass is the mass of one mole of a substance, found from its chemical formula and the periodic table.

Volume conversion is important: divide millilitres by

1000

to get litres. Keep units beside measured values and through the calculation. The final unit

ext{mol/L}

shows that the result is a concentration, not an amount of substance.

When comparing two samples, use the same units and state the basis for comparison. A larger concentration means more solute particles per litre of solution. It does not necessarily mean that the sample contains more total solute, because the samples may have different volumes.

c=\frac{n}{V}

Molar concentration compares amount of solute with volume of solution.
Use litres for volume in the concentration relationship.
Keep units in the calculation and report a sensible number of significant digits.

4. Planning an investigation and interpreting results

A strong investigation question is specific. For example: how does the amount of a particular solid added affect whether it dissolves in a fixed volume of water at a fixed temperature? The question names what changes and what evidence will be collected.

Identify the variable you change, the property you observe or measure, and the conditions you keep the same. A variable is a factor that can change. For a solubility investigation, record the mass added, solvent volume, temperature, mixing conditions, and whether undissolved solid remains. Repeat observations can help you notice inconsistent results.

Use qualitative and quantitative evidence together. A measured mass gives a numerical amount. The observation of remaining solid helps interpret whether more solute dissolved. If the goal is to compare concentrations, calculate each concentration using the same units and show the measurements used.

A conclusion should answer the investigation question and refer to evidence. It should not claim more than the observations support. For example, visible solid remaining after mixing supports the conclusion that not all of the added solid dissolved under those conditions. It does not by itself establish an exact solubility value.

A fair comparison keeps relevant conditions constant.
Record measurements with units and observations in clear language.
Connect conclusions to the evidence and the conditions tested.

Worked example

Finding concentration from a measured mass

A student dissolves

5.85\ \text{g}

of sodium chloride,

\mathrm{NaCl}

, and makes enough solution to have a final volume of

0.500\ \text{L}

. Calculate the molar concentration. The molar mass of sodium chloride is

58.5\ \text{g/mol}

.

Convert mass to amount
Concentration needs amount in moles. Divide the measured mass by the molar mass. The grams cancel, leaving moles.
$n=\frac{5.85\ \text{g}}{58.5\ \text{g/mol}}=0.100\ \text{mol}$
Use the solution volume
The stated volume is already in litres and refers to the final solution volume. Substitute the amount and volume into the concentration relationship.
$c=\frac{0.100\ \text{mol}}{0.500\ \text{L}}=0.200\ \text{mol/L}$
Report the result
The measured values support three significant digits, so report the concentration as $0.200\ \text{mol/L}$ . The final volume is solution volume, not just the volume of water used.

Answer: The sodium chloride solution has a molar concentration of

0.200\ \text{mol/L}

.

Check: The units are moles divided by litres. The result is consistent with

0.100\ \text{mol}

of solute in half a litre of solution.

Common mistakes and how to avoid them

Saying that a dissolved solid has disappeared.

Correction: Its particles have spread through the solvent. The solid may no longer be visible, but its substance remains in the solution.

Calling every clear liquid a solution of a known substance.

Correction: Clarity is an observation, not an identification test. State only what the evidence supports.

Using the volume of water instead of final solution volume in a concentration calculation.

Correction: Use the total final volume of the solution, expressed in litres.

Comparing solubility results without controlling temperature.

Correction: State and keep temperature constant because solubility depends on conditions.

Leaving units off measurements or the final answer.

Correction: Include units throughout. A concentration should include units such as

\text{mol/L}

.

Lesson summary

A solution is a uniform mixture of solute and solvent particles.
Qualitative observations describe features such as clarity or undissolved solid; quantitative evidence uses measurements and units.
Solubility is the greatest amount that dissolves under stated conditions. Unsaturated, saturated, and supersaturated describe the amount dissolved relative to that limit.
Molar concentration is the amount of solute in each litre of solution.
A useful investigation controls conditions, records evidence, and limits conclusions to what the evidence supports.

Check your understanding

Question 1

A clear mixture contains a dissolved solid. Which statement best describes the solid?

Its particles have spread among the solvent particles.
Its particles have been destroyed.
It must have become a liquid layer.
It is necessarily present in a saturated amount.

Show answer and explanation

Its particles have spread among the solvent particles.

Dissolving spreads solute particles through the solvent. A clear appearance alone does not show whether the solution is saturated.

Question 2

A student wants to compare how much of a solid dissolves at two temperatures. Which condition should be kept the same?

The amount of solvent
The temperature
Both the solvent amount and the temperature
Neither condition needs to be controlled

Show answer and explanation

The amount of solvent

To compare the effect of temperature, keep the solvent amount the same while changing temperature. Temperature is the factor being investigated.

Question 3

A solution contains

0.30\ \text{mol}

of solute in

0.60\ \text{L}

of solution. What is its concentration?

$0.20\ \text{mol/L}$
$0.50\ \text{mol/L}$
$1.8\ \text{mol/L}$
$2.0\ \text{mol/L}$

Show answer and explanation

0.50\ \text{mol/L}

Divide amount by volume:

0.30\ \text{mol}/0.60\ \text{L}=0.50\ \text{mol/L}

. The units are moles per litre.

Key terms

Solution: A uniform mixture in which solute particles are spread through a solvent.
Solute: The substance that dissolves in a solvent.
Solvent: The substance that does the dissolving.
Solubility: The greatest amount of a solute that dissolves in a stated amount of solvent under stated conditions.
Qualitative evidence: An observation described without a numerical measurement.
Quantitative evidence: Evidence recorded as a number with an appropriate unit.
Molar concentration: The amount of solute, in moles, per litre of solution.

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Published by DoAssignment. This AI-assisted lesson follows Ontario Grade 11 Chemistry (SCH3U), expectation E2.4. It is a study resource, not an official curriculum publication.

Before publication, the draft is checked for structure, mathematical or chemical notation, calculations, course boundaries, and readability, and then requires administrator approval. Errors can still occur, so corrections are welcomed.

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E2.4 · Investigate qualitative and quantitative solution properties

Ontario Grade 11 Chemistry

Ontario Grade 11 Chemistry — E2.4

What you will learn

1. From mixtures to solutions

2. Qualitative evidence and solubility

3. Quantitative solution properties

4. Planning an investigation and interpreting results

Finding concentration from a measured mass

Common mistakes and how to avoid them

Lesson summary

Check your understanding

Question 1

Question 2

Question 3

Key terms

Continue through SCH3U

About this lesson and its review