username2905396
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Hi, I have a chemistry exam on Tuesday. I'm little bit confused as how I could identify whether a substance is an acid, alkaline or salt:

Acid+Alkali-->Salt + water.
Acid+Metal--> Salt+hydrogen.
Acid+metal carbonate--> salt+water+carbondioxide
Acid+metal--> salt+water

How would I know what would be a salt and how do I know which reactant is acid/alkali?
Many thanks
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lizardlizard
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Do you know what form the reactants will be given in? e.g.
HCl + NaOH -> H2O + NaCl
or
Hydrochlorid acid + Sodium hydroxide -> Water + Sodium chloride
If you're given the names, a lot of acids have "acid" in their name, and a lot of alkalis have "hydroxide".
If you're given formula, you should know 3 main acids, sulfuric acid H2SO4, nitric acid HNO3, and hydrochloric acid HCl. One rough definition is that a lot of acids will only contain non-metals, whereas a lot of alkalis contain metals and non metals e.g. KOH.
This is a really difficult question to answer, and even at higher levels there is no absolute definition of which chemicals are alkalis. I highly doubt at GCSE level they would give you a chemical formula and expect you to work out if it is an acid or alkali.
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A.J.Rimmer
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Acids produce H+ ions when added to water, alkalis produce OH- (hydroxide) ions when added to water, so if you have the formulae that can help you decide.
For example, HCl is hydrochloric acid (H+ ion and Cl- ion), and NaOH is sodium hydroxide, an alkali (Na+ ion, OH- ion).
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lizardlizard
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(Original post by A.J.Rimmer)
Acids produce H+ ions when added to water, alkalis produce OH- (hydroxide) ions when added to water, so if you have the formulae that can help you decide.
For example, HCl is hydrochloric acid (H+ ion and Cl- ion), and NaOH is sodium hydroxide, an alkali (Na+ ion, OH- ion).
This is completely true, but you have to be really careful with this definition, as you have things like carboxylic acids (for example HCOOH) which would seem like an alkali due to the OH at the end, but are actually acids. Also remember that not every compound with H is an acid, for example methane CH4 is not acidic or alkaline.
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