Science Lab

Exp. 01 · Acids & bases

Red cabbage pH indicator

Time: about 40 minutes · Suggested ages: 4+ with an adult · Mess: low (can stain)

Red cabbage juice changes color depending on whether a liquid is acidic, neutral, or basic. Kids can sort kitchen liquids by color and discover the pH scale for themselves.

Materials

• About 2 cups chopped red cabbage (roughly a quarter of a head)
• About 2 cups hot water from a kettle
• A heat-safe bowl or large jar, and a strainer
• 5 or 6 clear cups or small jars, plus masking tape and a marker for labels
• Test liquids: lemon juice, white vinegar, plain water, and baking soda solution (1 teaspoon baking soda stirred into 1/2 cup water)
• Optional: sparkling water or clear soda water
• Measuring spoons and safety goggles

Steps

1. Put on goggles. An adult pours the hot water over the chopped cabbage in the heat-safe bowl.
2. Let it steep for about 15 minutes, until the water is deep purple, then let it cool.
3. Strain out the cabbage. The purple liquid is your indicator.
4. Label one clear cup for each test liquid and pour about 1/4 cup of indicator into each.
5. Predict which liquids will change the color, and write the predictions down.
6. Add about 1 tablespoon of each test liquid to its labeled cup and swirl. Record the color you see.
7. Line the cups up from pink to green and compare the results with your predictions.
8. Bonus: add vinegar a little at a time to the baking soda cup. Watch it fizz and shift back toward purple and pink.

The science behind it

Red cabbage contains pigments called anthocyanins. Their molecular structure changes slightly depending on how acidic or basic a solution is, and each form absorbs light differently, so we see a different color.

Acids such as lemon juice and vinegar turn the indicator pink to red. Plain water leaves it purple, close to neutral. Bases such as baking soda solution turn it blue or blue-green. Chemists use the pH scale to describe this: below 7 is acidic, 7 is neutral, and above 7 is basic.

Exp. 02 · Solutions & crystals

Growing sugar crystals

Time: 30 minutes to set up, then 3 to 7 days · Suggested ages: 5+ (adults handle the hot syrup) · Mess: low

Dissolve a lot of sugar in hot water, let it cool, and give the extra sugar somewhere to go. Over several days, crystals grow on a stick you can observe and measure.

Materials

• 1 cup water
• About 3 cups granulated sugar, plus a little extra for seeding
• A saucepan and a wooden spoon
• A clean, heat-safe glass jar (a tall, narrow jar works well)
• A wooden skewer and a clothespin
• A paper towel or coffee filter to cover the jar
• Optional: food coloring

Steps

1. Seed the skewer: dip the bottom few inches in water, roll it in sugar, and let it dry completely (at least an hour, or overnight). These grains give new crystals a place to start.
2. An adult heats the water in the saucepan until it simmers, then stirs in the sugar about 1/2 cup at a time, letting each addition dissolve before adding more.
3. Keep stirring until the liquid is clear, then take it off the heat. Add a drop of food coloring if you like.
4. Let the syrup cool for about 20 minutes. Meanwhile, warm the jar with hot tap water so it doesn’t crack, then empty it.
5. An adult carefully pours the warm syrup into the jar.
6. Clip the clothespin to the skewer and rest it across the mouth of the jar so the skewer hangs about an inch above the bottom without touching the sides.
7. Cover the jar loosely with a paper towel and set it somewhere it won’t be bumped.
8. Check every day and record what you see. Draw, measure, or photograph the crystals. If a crust forms on top, gently break it.

The science behind it

Hot water can dissolve much more sugar than cold water. As the syrup cools, it holds more dissolved sugar than it normally could at that temperature. Chemists call this a supersaturated solution.

The extra sugar molecules come out of solution and attach to the seed grains on the skewer, lining up in an orderly, repeating pattern: a crystal. Slow evaporation over the next few days adds more. A still jar and slow cooling give bigger, neater crystals.

If nothing grows after two or three days, the solution probably wasn’t saturated. Reheat it, dissolve a bit more sugar, and try again with a fresh seeded skewer.

Exp. 03 · Reaction rates

Baking soda and vinegar: reaction rates

Time: about 45 minutes · Suggested ages: 7+ · Mess: medium (use a tray)

Does temperature change how fast a reaction happens? Kids control the variables, collect data, and graph the results. This is a real experiment, not just a fizzy demo.

Materials

• White vinegar (1 1/2 cups total)
• Baking soda (3 tablespoons total)
• 3 identical empty plastic bottles (16 to 20 oz)
• 3 identical balloons and a small funnel
• 3 bowls for water baths: ice water, room-temperature water, and warm tap water
• Measuring cup and spoons, masking tape and a marker, a timer
• A flexible measuring tape (or string and a ruler)
• Safety goggles and a tray or baking sheet

Steps

1. Put on goggles. Use the funnel to put 1 tablespoon of baking soda into each balloon.
2. Pour 1/2 cup of vinegar into each bottle. Label the bottles Cold, Room, and Warm.
3. Stand each bottle in its water bath for 10 minutes. Warm tap water is enough; don’t heat vinegar on the stove.
4. Predict: which balloon will inflate fastest? Will they all end up the same size? Write your predictions down.
5. Stretch a balloon over the neck of each bottle, letting it hang to the side so the baking soda stays in the balloon.
6. Lift one balloon so the baking soda falls in, and start the timer.
7. Measure around the widest part of the balloon at 15, 30, and 60 seconds, and again when the fizzing stops.
8. Repeat with the other two bottles. Record everything in a table and draw a graph of balloon size over time.

The science behind it

Baking soda (sodium bicarbonate) reacts with the acetic acid in vinegar to make carbon dioxide gas, water, and sodium acetate. The carbon dioxide inflates the balloon.

In warmer vinegar, the molecules move faster, so they collide more often and with more energy. That makes the reaction go faster, and the balloon inflates more quickly.

The total amount of gas depends on how much baking soda and vinegar you used, so the final balloon sizes should be fairly close. This is the difference between how fast a reaction goes (its rate) and how much product it makes. If the warm balloon ends up a little bigger, that’s a bonus lesson: warm gas takes up more space, and less carbon dioxide stays dissolved in warm liquid.