Using percentages in chemistry

Formulations

Formulations are essentially a mixture of different components. They are made by mixing substances according to a specific formula. A formulation usually contains one or more active ingredients such as fragrance in perfumes, therapeutic drugs in medicines and oral care agents in toothpastes.

Paints are formulated according to their proposed use such as primer, undercoat or special finishes (matt, gloss, heat resistance, anti-corrosion, abrasion resistance). When producing the paints, each batch of ingredients is thoroughly mixed in large containers with the required additives. Up to 40000 dm3 can be made in a single batch. So, presenting the required ingredients as percentages can help chemists to both identify the differences between different types of paint at a glance and to work out the quantities required to make a specific batch.

Fertilisers

The percentage composition of N, nitrogen, P, phosophorus and K, potassium is usually shown on fertiliser packaging to help farmers and gardeners work out which fertliser to buy. Different crops, require different amounts of these essential elements for perfect growth.

The composition of air

The compostion of the air has been much the same for the last 200 million years. However, small changes in the percentage of greenhouse gases present, such as carbon dioxide can really effect our climate.

Gases in air % of the air
nitrogen 78.00
oxygen 21.00
carbon dioxide 0.04
water vapour varies
argon 0.93
other noble gases ~0.03

 

Quantitative chemistry

Percentages are widely used in quantitative chemistry. To explore this topic in more detail and see more examples including the calculations of empirical formulae and percentage yields, subscribe to the Quantitative chemistry (Reacting masses) course.

Percentage yield is caluclated using the formula

% yield = (actual yield/ theoretical yield) x 100

 

 

 
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