Experiment Plan. How much energy is transferred as heat when acids react with alkalis?

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Chemistry: how much energy is transferred as heat when acids react with alkalis?


In this investigation, I will be looking at the heat levels during the process of neutralisation, where you react and acid and an alkali together.

What are acids?

An acid is a chemical substance that neutralizes alkalis, dissolves some metals, and turns litmus red. Acids can come in each of the three states when they’re pure. They can be solids, such as citric acid, they can be liquids, for example sulphuric acids, or they can be like hydrochloric acid, which is a gas.  To identify if a solution is acidic .You can use the pH scale, and some litmus paper. On a pH scale, an acid will be less than 7 – the lower the pH number, the stronger the acid. To use it, you have to see what colour the paper turns, and then compare it against the scale. The darker the colour, the lower the pH number, and the lower the pH number, the stronger the acid. There are two different kinds of acids: organic and mineral acids. Organic acids are molecular and consist of carbon and oxygen atoms. Mineral acids come from inorganic/mineral sources. All pure acids are mineral acids.

Throughout the group of acids, they all show some common properties. The common properties are: they’re corrosive to metal and skin, they turn litmus paper red, they have a pH of less than 7, they contain H+ ions and they’ll donate these during a reaction.

What are alkalis?

An alkali is a chemical compound that neutralizes or effervesces with acids and turns litmus blue. They are sold as tablets to treat things such as heartburn, as they neutralise the acid. Common alkalis include sodium hydroxide, potassium hydroxide and calcium hydroxide. They are identified in the same way as acids are – by using a pH scale and litmus paper. However, they will have a pH of anything above 7, up to 14. They also turn the paper blue – the darker the colour, the stronger the alkali. Like acids, there are some similar properties that are shown across the entire group. They all produce heat when they’re heated, they contain OH- ions and will donate them when they react and they all have pH numbers of 8 or above.

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How does neutralisation work?

Neutralisation occurs when an acid reacts with an alkali. The products are always a form of salt, e.g. NaCl, and water. This is because when the acids dissolve, they donate H+ ions and the alkalis donate OH- ions, which react to form H20, as shown in this equation:

Hydrogen +Hydroxide         Water

H+ (aq) + OH- (aq)         H20 (l)

The salt is always formed when the positive ion from the alkali reacts with the negative ion from the acid. For example, when you react Sodium Hydroxide and Sulphuric Acid, the positive ion from the alkali (sodium) ...

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