Soda…

There is a group of compounds based around the element sodium whose common names all include the word soda.

• Sodium bicarbonate – baking soda
• Sodium carbonate – washing soda
• Sodium hydroxide – caustic soda

There are lots of other sodium compounds such as sodium chloride that don’t get soda in their name – although glass made with sodium oxide is called soda glass.

Sodium bicarbonate is a soluble, white compound with a slightly alkaline pH of about 10. It has the chemical formula NaHCO₃ and is also sometimes called sodium hydrogen carbonate. When heated, it decomposes releasing carbon dioxide. This makes it useful for making cakes and pastries rise by filling them up with carbon dioxide bubbles. It can also react with vinegar or other acidic ingredients to add froth to batter.

Sodium carbonate has a number of important industrial uses, especially in the manufacture of glass. It is mixed with calcium hydroxide (slaked lime) and silica (silicon oxide/sand) and heated to about 1700°C then rapidly cooled. This process produces glass called soda-lime glass. This form is the most common kind of glass in everyday use for jars, bottles and window panes.

Sodium carbonate is also known as washing soda and in solution it is effective at removing grease, oil and alcohol stains that water alone would not be able to dissolve. It is added to washing powder to help combat the effects of ‘hard water’ that prevent the soap from lathering properly. Sodium carbonate is a strong alkali with a pH of about 12. It can be mixed with an organic acid such as malic acid, tartaric acid or citric acid to make sherbet. When the mixture hits your tongue, the acid dissolves and reacts with the sodium carbonate producing carbon dioxide gas. This produces the fizzing sensation in your mouth.

Sodium hydroxide is a strong alkali with a pH of about 14. It attacks flesh so needs to be handled with great care to avoid chemical burns. It is highly soluble, and exothermic as it dissolves. Sodium hydroxide is used in a variety of industrial processes, such as paper manufacture. It is also an ingredient in drain and oven cleaner. It can be used to scrub acidic gases (such as SO₂ or CO₂) from factory fumes.

It will also react with acidic solutions to produce a salt and water.

Sodium carbonate and sodium hydroxide solutions can both strip the protective oxide layer from aluminium. This leaves the aluminium free to react with water producing hydrogen gas.

Questions…

1. From what fruits could you extract (a) citric acid (b) tartaric acid (c) malic acid?
2. Name a chemical that thermally decomposes to release oxygen.
3. The three most abundant elements on Earth all get a mention in the post above. What are they?
4. What harmful environmental problem is reduced by scrubbing the sulphur dioxide out of industrial fumes?
5. Why did the fellow in the video not collect very much gas in his upturned glass?