C. Chemistry: The Nature of Matter · Atoms, Elements and Compounds

Chemistry at Home: Household Products, Safety Symbols and pH

C2.6 A1.5 A1.2About 75 minutes

Learning goals

I can name some compounds found in household products and describe their properties.
I can read Canadian hazard symbols on consumer products and know what WHMIS is for.
I can describe acids and bases using the pH scale and test household products with an indicator.
I can explain why some cleaning products must never be mixed.

Words to know

acid
A compound that forms a solution with a pH below 7. Acids taste sour, turn blue litmus paper red, and react with baking soda to make carbon dioxide gas.

base
A compound that forms a solution with a pH above 7. Bases taste bitter, feel slippery and turn red litmus paper blue.

pH scale
A scale, usually from 0 to 14, that shows how acidic or basic a solution is. 7 is neutral.

indicator
A substance that changes colour depending on whether a solution is acidic, neutral or basic, such as litmus paper or red cabbage juice.

neutralization
A reaction between an acid and a base that cancels out their acidic and basic properties.

WHMIS
The Workplace Hazardous Materials Information System: Canada's system of labels, pictograms and Safety Data Sheets for hazardous products used at work and in school labs.

Safety Data Sheet (SDS)
A document that gives detailed information about a hazardous product's dangers, safe handling and first aid.

Look under your sink

Your home is full of chemistry. The kitchen and bathroom hold dozens of elements and compounds: table salt (sodium chloride, NaCl), baking soda (sodium hydrogen carbonate, NaHCO₃), vinegar (a solution of acetic acid in water), sugar (sucrose, C₁₂H₂₂O₁₁), hydrogen peroxide (H₂O₂ dissolved in water) and bleach (a solution of sodium hypochlorite). Each one is useful because of its properties, and some can be harmful if used the wrong way.

Today you will learn to read the safety information on product labels and to sort household products using the pH scale.

Product	Main compound (formula)	Useful property
Table salt	sodium chloride (NaCl)	Dissolves in water; adds flavour; lowers the freezing point of water (used on icy sidewalks)
Baking soda	sodium hydrogen carbonate (NaHCO₃)	Reacts with acids to make carbon dioxide gas, which makes muffins rise
Vinegar	acetic acid (CH₃COOH), about 5% in water	Acidic; dissolves hard-water deposits (scale) in a kettle
Hydrogen peroxide (3%)	H₂O₂ in water	Breaks down into water and oxygen gas; used as a mild antiseptic
Rubbing alcohol	isopropyl alcohol (C₃H₈O) in water	Evaporates quickly; dissolves oils; flammable
Chlorine bleach	sodium hypochlorite (NaOCl) in water	Removes colour and kills many germs; corrosive

Some compounds in household products. You do not need to memorize these formulas, but notice that each is a pure compound with a fixed formula, even though the product is often a solution.

Canadian hazard symbols on consumer products

Products sold for home use in Canada must show hazard symbols when they are dangerous. Each symbol has two parts:

The picture tells you what kind of hazard: a skull and crossbones (poison), a flame (flammable), a hand being eaten away (corrosive), or a bursting shape (explosive).
The border tells you where the danger is. An octagon (stop-sign shape) means the contents are dangerous. A triangle means the container is dangerous, for example an aerosol can that could burst if heated or punctured.

A signal word under the symbol, such as CAUTION or DANGER, tells you how serious the hazard is. Always read the directions and first-aid information on the label.

The border shape tells you whether the danger is the product inside or the container itself. (The real symbols show the pictures described; this sketch uses words instead.)

WHMIS: safety at work and in the science lab

In workplaces and school science labs, Canada uses WHMIS (the Workplace Hazardous Materials Information System). WHMIS has three main parts:

Labels on containers, with pictograms: black symbols inside a red border shaped like a diamond (a square standing on one corner).
Safety Data Sheets (SDS) that explain each product's hazards, how to store and handle it, and first aid.
Training, so workers know what the symbols mean.

Workers in skilled trades such as auto service, hairstyling, welding, plumbing and cleaning use WHMIS every day. You will see WHMIS labels on bottles in your school's science lab.

Acids and bases

Many household products are acids or bases.

Acids taste sour (lemons, vinegar), turn blue litmus paper red, and react with baking soda to make bubbles of carbon dioxide. Strong acids are corrosive.
Bases taste bitter and feel slippery (soap), and turn red litmus paper blue. Strong bases, such as drain cleaner and oven cleaner, are corrosive too.
Never taste or touch an unknown substance to test it. We know these properties from safe lab tests.

The pH scale measures how acidic or basic a solution is. It usually runs from 0 to 14:

pH below 7: acidic. The lower the number, the more acidic.
pH 7: neutral (pure water).
pH above 7: basic. The higher the number, the more basic.

Each step of 1 on the pH scale means 10 times more (or less) acidic. A solution with pH 3 is 10 times more acidic than one with pH 4, and 100 times more acidic than one with pH 5.

Acids sit on the left (below 7) and bases on the right (above 7). Values are approximate, since products vary.

Neutralization

When an acid and a base react, they neutralize each other. The products are water and a type of compound called a salt. An antacid tablet (a base) neutralizes extra stomach acid; gardeners spread lime (a base) on soil that is too acidic. You will study neutralization in more detail in Grade 10 science.

Never mix cleaning products. Mixing bleach with ammonia cleaners makes toxic gases called chloramines. Mixing bleach with acids (such as vinegar or some toilet-bowl cleaners) releases toxic chlorine gas. These are chemical properties that can hurt people, which is why labels say "Do not mix with other chemicals."

Worked example

Example 1: Read a label

A drain cleaner has a corrosive picture inside an octagon, with the word DANGER. What does the label tell you, and how should it be used and stored?

Picture: corrosive. The product can burn skin and eyes and damage materials.
Octagon border: the danger is the contents, not the container.
DANGER: a serious hazard that can cause permanent injury.
Safe use: a grown-up should use it, wearing gloves and eye protection, following the directions exactly, never mixing it with other products, and storing it in its original container, locked away from children.

The contents are seriously corrosive. Handle only with protection, never mix, and store safely in the original container.

Worked example

Example 2: Interpret indicator results

A student adds red cabbage indicator to four colourless solutions. A turns pink, B stays purple, C turns blue-green, D turns red. List them from most acidic to most basic.

Use the colour chart: red ≈ pH 1–2, pink ≈ pH 3–4, purple ≈ neutral, blue-green ≈ pH 9–10.
Most acidic = lowest pH: D (red), then A (pink).
Next is B (purple, about neutral), then C (blue-green, basic).

D, A, B, C. D and A are acids, B is about neutral, and C is a base.

Red cabbage juice contains natural pigments that change colour with pH. Here the colours themselves are the information, so the chart uses real colours.

Hands-on activity

Make a red cabbage indicator

You need: a grown-up, about 2 leaves of red cabbage, a knife and cutting board (grown-up only), a heat-proof bowl, hot water from a kettle (grown-up pours), a strainer, 6 clear cups or glasses, a spoon, labels, and test liquids: lemon juice, white vinegar, tap water, milk, baking soda dissolved in water (1/2 teaspoon in 1/4 cup), and a little dish soap in water.

Do not test bleach, drain cleaner, oven cleaner or ammonia. They are corrosive and can react dangerously. Wear eye protection and do not drink anything.

The grown-up chops the cabbage, puts it in the bowl, and covers it with hot water. Let it stand for 10 minutes, then strain it. The purple liquid is your indicator.
Pour about 2 tablespoons of indicator into each cup and label the cups.
Add about 1 tablespoon of each test liquid to its own cup. Stir with a clean spoon each time.
Record the colour and use the chart to estimate the pH.
Put the cups in order from most acidic to most basic.
Extra: slowly add vinegar to the baking-soda cup. What happens to the colour and why?

What to look for: lemon juice and vinegar turn pink or red (acids); tap water stays about purple (close to neutral); milk stays purple or slightly pink (slightly acidic); baking soda solution turns blue to blue-green (basic). In the extra step, bubbles form and the colour moves back toward purple or pink: the acid is neutralizing the base. Pour everything down the sink with lots of water when done.

Just for fun

Why did the bleach and the ammonia get separate seats on the bus?

Because when they get together, the air gets toxic. (That is exactly why the label says never mix.)

Your turn

What does an octagon border around a hazard symbol mean? What does a triangle border mean?

A solution has a pH of 9. Is it acidic, neutral or basic?

How many times more acidic is a solution of pH 2 than a solution of pH 4?

Give two properties of acids and two properties of bases (that can be tested safely).

What does WHMIS stand for, and where is it used?

Why must you never mix bleach and vinegar?

Baking soda is NaHCO₃. Is baking soda an element, a compound or a mixture? How do you know?

More practice: warm-up

What pH is neutral?

Is lemon juice an acid or a base?

What colour does red litmus paper turn in a base?

What does the flame picture on a label mean?

What colour is red cabbage indicator in a neutral solution?

More practice: on your own

Rank from most acidic to most basic: bleach (pH ≈ 12.5), milk (≈ 6.5), vinegar (≈ 3), baking soda solution (≈ 8).

An aerosol can of spray paint shows a flame inside an octagon and a bursting symbol inside a triangle. Explain both.

Why is a gardener's lime (a base) added to soil that is too acidic?

Why are WHMIS Safety Data Sheets useful even when a product has a label?

A student tests an unknown liquid and the cabbage indicator turns pink. She concludes it is safe because "it's only a weak acid." Is this good reasoning?

Challenge

Solution X has pH 3. Solution Y is 1000 times less acidic. What is Y's pH, and is it acidic, neutral or basic?

Explain why vinegar removes white hard-water scale (mostly calcium carbonate) from a kettle, using the properties of acids. What would you observe?

Design a fair test to find out which of two antacid brands neutralizes more acid. Name the independent, dependent and controlled variables.

Check your understanding

Quiz

A product shows a corrosive symbol inside an octagon. What does the octagon tell you?

Which pH describes the most acidic solution?

Which household product is a base?

Why must bleach never be mixed with ammonia cleaner?

What is a WHMIS Safety Data Sheet?

A solution of pH 5 is how many times more acidic than one of pH 7?

For parents and teachers

Big idea: C2.6 includes the properties of compounds in common household products, and A1.5 asks students to apply safe practices, including WHMIS. Students should finish this lesson able to read a consumer hazard label and explain acids, bases and pH.

Common difficulties:

Thinking a higher pH means more acidic. Lower pH = more acidic.
Thinking pH 4 is "twice as acidic" as pH 8. Each step is a factor of 10.
Mixing up the border meanings. Octagon = contents; triangle = container.

Safety at home: please supervise the red cabbage activity (knife and hot water). Only test the food-safe liquids listed. This is a good moment to check that cleaning products at home are stored in original containers and out of reach of younger children, and to talk about never mixing cleaners. Many labels tell you to contact a poison control centre if the product is swallowed; look up the number for the Ontario Poison Centre and keep it handy.