Colourless, odorless gas, 1 litre of which weighs about 1.98 g at 0° and 760 mm of mercury. Under a pressure of about 59 atmospheres it may be condensed to a liquid, a portion of which forms a white solid (Dry Ice) upon rapid evaporation.

Carbon Dioxide (CO2) is measured in parts-per-million (ppm) and reported in units of micromol mol-1 (10-6 mol CO2 per mol of dry air). Measurements are directly traceable to the WMO CO2 mole fraction scale.

Carbon dioxide has no liquid state at pressures below 5.1 atm. At 1 atm it is a solid at temperatures below −78 °C. In its solid state, carbon dioxide is commonly called dry ice. CO2 is an acidic oxide: an aqueous solution turns litmus from blue to pink.

Carbon dioxide is a colorless gas that is heavier than air. At low concentrations, carbon dioxide gas has no odor. At high concentrations, it has a sharp, acidic smell. At normal temperatures, carbon dioxide Welders use carbon dioxide to help prevent impurities, like rust, from forming at welds.

Carbon dioxide is used as a refrigerant, in fire extinguishers, for inflating life rafts and life jackets, blasting coal, foaming rubber and plastics, promoting the growth of plants in greenhouses, immobilizing animals before slaughter, and in carbonated beverages.

Hydrogencarbonate indicator is used to show carbon dioxide concentration in solution. The table shows the colour that the indicator turns at different levels of carbon dioxide concentration….Gas exchange experiments.

When submerged in an aquarium, the airspace eliminates contact between the indicator solution and the aquarium water. When CO2 is injected into the aquarium, the CO2 will out gas from the aquarium water into the airspace of the drop checker. As CO2 enters the air, it is absorbed into the indicator solution.

Carbon dioxide, even in the concentrations found in exhaled air, will dissolve in the indicator to form carbonic acid, a weak acid, which will lower the pH and give the characteristic colour change.

Carbon dioxide lowers the pH of water once it dissolves in it. This is because it forms a weak acid upon dissolving and that acid frees up H+ ions. Placing a plant that is performing photosynthesis in a solution will result in the conversion of dissolved CO2 (carbon dioxide) to oxygen gas.

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The interactions among these opposing compounds and processes determine pH. Carbon dioxide is particularly influential in regulating pH. It is acidic, and its concentration is in continual flux as a result of its utilization by aquatic plants in photosynthesis and release in respiration of aquatic organisms.

CO2 is not an acid itself, since it does not contain ions of hydrogen (H+). CO2 becomes carbonic acid in water. Carbonic acid (H2CO3) is a weak, H+-splitting acid. Carbonic acid, a weak acid that acidifies the solution, is formed when some of the carbon dioxide dissolves in the water.

Carbon dioxide is a great choice for use in soda products as it easily absorbs into a liquid including soft drinks to forms tiny bubbles. The CO2 also serves as a protective measure that keeps the soft drink fresh and prevents the growth of bacteria in the liquid while stored.