# Question on neutralising an acid+base.?

For an acid and a base to be "neutalised" and produce a "salt" how is it determined what quanatities of the acid and base are needed for the reaction to occur? Importantly, does water need to be added for the reaction to occur as the acid (HCl) already contains water? For example HCl+NaOH->NaCL+H2O I am new to chem so any help would be appreciated.

Usually you will be dealing with aqueous solutions of acid and base - so water is already around. but that doen't mean that water isn't formed when you do a reaction like:

HCl(aq) + NaOH(aq) --> NaCl(aq) + H2O(aq)

water IS a product of the reaction and MUST be added to balance the equation.

Sometimes you can do acid-base reactions without ANY water. Say,

NH3(g) + HCl(g) --> NH4Cl(s)
water need not be added as a solvent but it will make them both weaker if that is what you want.

If you have a strong acid and a strong base (like your example) than equal quantities will give a complete(ish) reaction

All neutralisation reactions are exothermic.
Okeydokey then - pH depends on the concentration of protons in solution (or hydronium ions...whichever you like better! It depends on which acid/base theory you're going by). When that concentration reaches a molarity of 1x10^-7 then the solution has a pH of 7 since pH = the negative log of the concentration of protons in solution.

HCl and NaOH react in a one to one ratio (can be found in the balanced equation for the reaction). Therefore, equimolar amounts (same amount in moles) of each neutralize each other, leaving you with saltwater with a pH of 7.

No, you do not need to add water to aqueous solutions of HCl and NaOH. The only thing that you would need to add water to is solid NaOH in order to make it into a solution (or you could find the mass of the moles of NaOH you need in order to neutralize the acid) and the HCl (technically, you'd add the HCl to the water since 'tis a gas in its purest state, but I digress). However, for NaOH and HCl to react, they must be ionized or at least in a state that they would be capable of going into aqueous solution. Gases have molecules, as do solids, but liquids ionize.

Any questions on that? Hope it helps!

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