Acids and AlkalisChapter 10Chemistry(1st week)

- Ancient Egyptians and Greeks that some substances taste sour and some feel slippery.

- Example: Vinegar is sour Lime made from burning of seashells is slippery. Potash found in the ashes of burnt wood is slippery.

- Scientists called the substance that tastes sour Acids.- The word acid came from the word Acidus which is the latin word

for sour.

- They also named the substances that feel slippery Alkali, which was developed from al-qaliy (an Arabic word meaning ‘the ashes’).

- N.B. A lot of investigative work in chemistry was done in Islamic countries, starting about 1200 years ago.

- The greatest of the muslim chemists at that time was Jabir ibn Haiyan.

Examples of Acids & Alkalis in our daily lives

Acids

- Most people think of acids as corrosive.

- This is true for many acids, but, some acids are found in our food (they give food their sour taste).

- Many acids are found in living things

Acids can be found in:

Plants Animals- Orange and lemon juice Citric acid

- Grapes Tartaric acid

- Citrus fruits and Ascorbic acid

blackcurrants (Vitamin C)

- Nettle stings Methanoic acid

- Mammalian stomach Hydrochloric acid

- Muscles during Lactic acid

vigorous exercise

- Urine Uric acid

- Ant sting Methanoic acid

Acid in vinegar- Ethanoic acid is found in vinegar.

- Ethanoic acid is also produced when wine becomes sour .

- Wine contains ethanol and some dissolved oxygen. Over a period of time oxygen reacts with ethanol and produces Ethanoic acid.

Ethanol + Oxygen Ethanoic acid

- The above chemical reaction happens more quickly if the wine bottle is left uncorked.

Organic acids and mineral acids

Acids can be classified into:

Organic acids Mineral acids- Are acids produced by plants and

animals.

- Are acids not produced by living things.- Their discovery began with the works of chemists

such as Geber.- The 1st mineral acid to be discovered was nitric

acid.- Nitric acid was used to separate silver and gold

(The silver dissolved but not the gold).- Later sulfuric acid and then hydrochloric acid

where discovered.

Alkalis

Examples of alkalis Uses

Sodium hydroxide and potassium hydroxide solution

Used in laboratories.

Calcium hydroxide (lime) Used in industries to make bleach and whitewash.

Weak sol. Of calcium hydroxide (lime water)

Test for co₂ in breath

- A concentrated solution has a greater amount of dissolved solute than a dilute solution.

- Example: A solution made up of 3 tablespoons of sugar

dissolved in 50 ml of water is concentrated. A solution made up of 1 tablespoon of sugar dissolved in 50 ml of water is dilute.

- A concentrated solution of an alkali is corrosive.

- A concentrated solution of an acid is also corrosive.

- A dilute solution of an acid or an alkali are irritant.

- Dilute solutions of alkali, such as sodium hydroxide, react with fat on the surface of the skin and change it into substances found in soap.

- House hold cleaners used of metals, floors and ovens contain alkalis and must be handled carefully.