Three cool tricks with dry ice

Just what can dry ice do? Let’s talk about it!

Safe­ty pre­cau­tions

Do not at­tempt! Per­form this ex­per­i­ment only with pro­fes­sion­al su­per­vi­sion.

Reagents and equip­ment

• glass con­tain­er;
• dry ice (sol­id car­bon diox­ide);
• can­dles;
• bowl of hot wa­ter;
• bal­loon;
• aque­ous al­ka­line so­lu­tions with in­di­ca­tors.

Step-by-step in­struc­tions

Put some dry ice in a glass con­tain­er and wait one minute. “Pour” the gas on some burn­ing can­dles. The can­dles should go out!

Place a few pieces of dry ice in a bal­loon. Put the bal­loon in some hot wa­ter. Af­ter a while, an in­vis­i­ble force should in­flate the bal­loon!

Take a few glass­es con­tain­ing in­di­ca­tors dis­solved in al­ka­line so­lu­tions: lit­mus, phe­nolph­thalein, and thy­mol blue. Drop a piece of dry ice into each glass. Af­ter a few min­utes, the so­lu­tions’ col­ors should change!

Process de­scrip­tion

Dry ice is a sol­id state of car­bon diox­ide. It forms at a tem­per­a­ture of -78.5 °C (-109°F). At room tem­per­a­ture, dry ice tran­si­tions rapid­ly from its sol­id to its gaseous state. Car­bon diox­ide gas is heav­ier than air, so it set­tles in a glass con­tain­er and can be “poured” on can­dles. Car­bon diox­ide doesn’t fa­cil­i­tate burn­ing, so the can­dles go out.

The warmer the medi­um, the faster the dry ice be­comes gaseous, so sol­id car­bon diox­ide eas­i­ly in­flates a bal­loon when put in hot wa­ter.

If you toss some dry ice in wa­ter, some of the car­bon diox­ide will dis­solve and form car­bon­ic acid:

СО₂ + Н₂О = Н₂СО₃

The lat­ter splits into ions in wa­ter, re­leas­ing some pro­tons:

Н₂СО₃ = НСО₃⁻ + Н⁺

НСО₃⁻ = СО₃²⁻ + Н⁺

These pro­tons neu­tral­ize the al­ka­line in­di­ca­tor so­lu­tions. When all of the al­ka­li is neu­tral­ized, the en­vi­ron­ment grad­u­al­ly be­comes acidic due to the ex­cess of pro­tons H+.

This makes the pH in­di­ca­tors change col­ors.