Solutes and solvents, conductivity, concentration, how fast things dissolve, solubility curves, and acids, bases and pH — with simulations and lots of practice. 7 free resources on this page.
Simulations, a click-the-graph solubility curve explorer, endless solubility curve practice, a household pH lab, worked examples and review for every part of SPS6.
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What you are learning
SPS6. Obtain, evaluate, and communicate information to explain the properties of solutions. a. Develop and use models to explain the properties (solute/solvent, conductivity, and concentration) of solutions. b. Plan and carry out investigations to determine how temperature, surface area, and agitation affect the rate solutes dissolve in a specific solvent. c. Analyze and interpret data from a solubility curve to determine the effect of temperature on solubility. d. Obtain and communicate information to explain the relationship between the structure and properties (e.g., pH, and color change in the presence of an indicator) of acids and bases. e. Plan and carry out investigations to detect patterns in order to classify common household substances as acidic, basic, or neutral.
Learning target
I am learning to explain the properties of solutions, interpret solubility curves and classify substances as acids, bases or neutral.
Success criteria
I will be successful when I can:
identify the solute and solvent and explain why some solutions conduct electricity
compare solutions as dilute or concentrated
investigate how temperature, surface area and stirring change how fast a solute dissolves
read a solubility curve and decide if a solution is unsaturated, saturated or supersaturated
explain acids and bases using H⁺ and OH⁻ ions, pH and indicator colors
classify household substances as acidic, basic or neutral
aSolute, solvent & ions
What dissolves, what does the dissolving, and why some solutions carry electricity.
bDissolving speed
Heat, smaller pieces and stirring all make a solute dissolve faster.
cSolubility curves
How much can dissolve at each temperature, read straight off a graph.
d–eAcids & bases
H⁺ and OH⁻ ions, the pH scale, indicators and household chemicals.
Solution: a mixture that is the same all the way through. The solute is the substance that dissolves (usually the smaller amount). The solvent does the dissolving (usually the larger amount). In salt water, salt is the solute and water is the solvent.
Part 1 · SPS6a
Solute and solvent: watch it dissolve
Pick something to drop into water. Water particles pull the solute apart, one particle at a time, until it is spread evenly through the whole beaker. Not everything dissolves, and not everything breaks apart the same way.
Ionic solutes like table salt split into charged particles called ions (Na⁺ and Cl⁻). Those moving charges let the solution conduct electricity.Molecular solutes like sugar spread out as whole molecules. They dissolve, but they make no ions, so sugar water does not conduct.Insoluble things like sand do not dissolve at all. They settle to the bottom. That is a mixture, but not a solution.
Particles in every drawing on this page are hugely enlarged, and the water particles are left out so you can see the solute.
Part 2 · SPS6a
Conductivity: which solutions light the bulb?
A conductivity tester is a battery, a bulb and two metal probes. The bulb only lights if charged particles (ions) can carry electricity through the liquid from one probe to the other. More ions → brighter bulb. A solute that makes ions is called an electrolyte.
BulbResponds
Predict. Distilled water is pure water. Tap water has tiny amounts of dissolved minerals. Which one lights the bulb, even a little?
Tap water glows faintly because its dissolved minerals form a few ions. Distilled water has almost no ions, so the bulb stays dark. Pure water is a very poor conductor. It is the things dissolved in water that let it conduct.
Part 3 · SPS6a
Concentration: dilute or concentrated?
Concentration is how much solute is in a certain amount of solution. Add more solute to the same water → more concentrated. Add more water to the same solute → more dilute. Mix a drink and watch the color and the crowding change.
ConcentrationResponds
Same water, more solute → more concentrated (darker, more crowded).
Same solute, more water → more dilute (lighter, more spread out).
Concentrated and dilute are comparisons: one solution is more concentrated than another.
Part 4 · SPS6b · Plan and carry out
How fast does it dissolve? Race two beakers
Three things change how fast a solute dissolves: the temperature of the water, the surface area of the solute (big lump or small pieces) and agitation (stirring or shaking). Set up two beakers, race them, and find out. A fair test changes only one thing.
Beaker A
0:00
Beaker B
0:00
Race
Beaker A
Beaker B
Result
No races yet. Set up both beakers and press Start the race.
🌡️ Temperature
Hot water particles move faster, so they hit the solute more often and harder and carry its particles away sooner.
🔨 Surface area
Crushing a cube into small pieces exposes more surface to the water, so more solute particles can be pulled off at once.
🥄 Agitation (stirring)
Stirring sweeps dissolved particles away and brings fresh water to the solute's surface again and again.
Faster is not more. Heat, crushing and stirring change how fast sugar dissolves. Only the temperature changes how much can dissolve in the end. That limit is called solubility, and it is what a solubility curve shows (next part).
Part 5 · SPS6c
Solubility curves: click the graph to mix a solution
A solubility curve shows the most solute that can dissolve in 100 g of water (about 100 mL) at each temperature. Pick a substance, then click anywhere on the graph. Your click sets the temperature (across) and how many grams you add (up). The beaker shows what happens.
Above the lineMore solute than the water can hold. The extra will not dissolve (supersaturated).
On the lineExactly as much as it can hold. The solution is saturated.
Below the lineLess than it can hold. More can still dissolve (unsaturated).
Point at the graph to read it. Click to mix.
Pick a substance and click the graph. Try a point above the line, one right on the line and one below it.
How to read a solubility curve
Find the temperature on the bottom axis.
Go straight up until you hit the curve for your substance.
Go straight across to the left axis and read the grams. That is the most that can dissolve in 100 g of water at that temperature.
Compare what is in the beaker to that number: less → unsaturated, equal → saturated, more → supersaturated (the extra settles out).
Most solids dissolve better in hot water, so their curves rise. Gases (NH₃ and SO₂ here) dissolve less in warm water, so their curves fall. That is why a warm soda goes flat faster. A few solids, like Ce₂(SO₄)₃, also fall. NaCl (table salt) barely changes.
Cooling a saturated solution lowers the limit, so solute comes back out as crystals. Use ❄ Cool 10 °C on a saturated KNO₃ solution and watch the crystals form.
Curve values are approximate, from standard reference solubility tables. Some books say points above the line are "supersaturated"; a solution can only truly hold that extra if it is cooled very carefully, and one bump makes the extra crystallize out.
Part 6 · SPS6c
Solubility curve practice (it never runs out)
Every question is made fresh from the graph, so you can practice as long as you want. Pick a skill, or leave it on Mixed. After you answer, the graph draws the guide lines so you can see exactly where the answer came from.
Part 7
Worked examples: solubility curves step by step
Make your own guess for each step before you reveal it.
Part 8 · SPS6d
Acids and bases: ions, pH and indicators
In water, an acid releases hydrogen ions (H⁺). A base releases hydroxide ions (OH⁻). The pH scale (0 to 14) tells you which ions win: below 7 is acidic, 7 is neutral, above 7 is basic. Indicators are dyes that change color depending on pH. Slide the pH and watch the ions and every indicator respond.
0 · most acidic7 · neutral14 · most basic
H⁺ hydrogen ionOH⁻ hydroxide ion
What each indicator shows at this pH
AcidspH below 7 · more H⁺Taste sour (lemons, vinegar), react with many metals, turn blue litmus red. Phenolphthalein stays colorless.
NeutralpH 7 · H⁺ and OH⁻ balancedPure water. Litmus does not change. Universal indicator is green.
BasespH above 7 · more OH⁻Taste bitter, feel slippery (soap), turn red litmus blue and phenolphthalein pink.
How the pH scale works: each step down the scale means about 10 times more H⁺. So pH 3 is 10 times more acidic than pH 4, and 100 times more acidic than pH 5. That is why the picture above can only hint at the difference. When an acid and a base are mixed, H⁺ and OH⁻ join to make water. That is called neutralization, and it pulls the pH toward 7.
Never taste or touch chemicals to test them. That is what indicators are for.
Part 9 · SPS6e · Plan and carry out
Household pH lab: acid, base or neutral?
Pick an indicator, then click a household substance to test it. Every result goes into your data table. Classify each one, check your work, then look for the pattern. Try more than one indicator on the same substance: some indicators can tell you more than others.
Substance
Results
Your call
No tests yet. Choose an indicator and click a substance.
Your substances on the pH scale
Look for the pattern. Which kinds of household things tend to be acids? Which tend to be bases?
Foods and drinks that taste sour (citrus juice, vinegar, soda, tomatoes, coffee) are acidic. Cleaners (soap, ammonia, bleach, drain cleaner) and antacids are basic. Pure water is neutral. Strong cleaners at the far ends of the scale are the most dangerous: never mix them.
Part 10
Solutions in real life
Decide which idea explains each one before you flip the card.
Part 11
Myth or fact?
The most common mix-ups about solutions, acids and bases. Decide, then see the truth.
Part 12
Practice: the whole unit
Ten questions at a time from every part of SPS6: solutes and solvents, conductivity, concentration, dissolving speed, solubility, acids, bases and indicators. Press New set any time for different questions.
Tobin
