Non 1:1 Ratio in Acid-Base Neutralization

[nolachrymose]

Hi all,

I'm pretty new to chemistry. Currently we're working on simply acid-base neutralizations, and I have a question. What happens when the ratio of hydroxides in the base to that of hydogens in the acid is >1. For instance, how would one predict the products of the following reaction:
$$HCl + Ca(OH)_2 \longrightarrow ?$$

I'm not really sure what the products would be (though I'm almost certain one would have to be water). I know how to do the reverse (when ratio hydrogen:hydroxide >1), but not the other way around. Any help is greatly appreciated. Thanks!

 

[dextercioby]

What is the general rule of acid-base neutralization?What are the products of reaction...?

Daniel.

 

[GCT]

acid base neutralizations involve the formation of water and the corresponding salt. The salt is calcium chloride. You know the products, now simply balance.

 

[dextercioby]

It would have been nicer,if he/she used his/her 'processor' to come to the right conclusions...

Daniel.

 

[nolachrymose]

But is that really all? My teacher had told us that for every hydrogen, a hydroxide is picked off. Thus, if the ratio is not 1:1, the reaction won't go to completion, and something other than a salt will be formed. Why is this not so then?

To give an example, she gave us the following reactants:
$$2H_3PO_4 + Ca(OH)_2$$

She said it would form water and calcium dihydrogen phosphate, rather than just water and calcium phopshate, because each hydroxide from calcium hydroxide picks off a single hydrogen to form water, and so two dihydrogen phosphates would be left to combine with calcium.

I figured the same principle would apply the same way if it were the opposite (i.e. there were not enough hydrogens for each hydroxide to pick off one and make water). If not, why is this so?

 

[dextercioby]

Now,there's a problem,incidentally the phosphoric acid is very weak and the first constant of acidity is the greatest (the other 2 are very small),so that' s why it will tend to form $Ca(H_{2}PO_{4})_{2}$...On the other hand,the hydrochloric one is amond the strongest acids and definitely it will ionize totally,as to form the $CaCl_{2}$...

Things are not as simple as they may look...


Daniel.

 

[dextercioby]

And one more thing...In such acid+base reactions,it will always come out a salt (non necessary "neutral") and water...

Daniel.

 

[GCT]

You're thinking about this too much. Simply write the equation showing the products and from there you can balance it out, you'll see what I mean.

 

[Borek]

I'm pretty new to chemistry. Currently we're working on simply acid-base neutralizations, and I have a question. What happens when the ratio of hydroxides in the base to that of hydogens in the acid is >1. For instance, how would one predict the products of the following reaction:
$$HCl + Ca(OH)_2 \longrightarrow ?$$

I think some of the answers other have posted are a little bit misleading.

Apart from neutral salts, like $CaCl_2$, there are also acid salts (like $NaHCO_3$) and base salts (like $CaOHCl$) - I hope I am using proper English names.

If you mix acid and base and you let the solution dry out you will have a salt - depending on the amount of substances mixed you may have any salt (or mixture of salts). Mixing solutions of 1 mole $Ca(OH)_2$ with 1 mole $H_3PO_4$ you will obtain 1 mole of $CaHPO_4$ - try to figure out by yourself what will happen if you use other amounts of acid and base.

In the solution situation may look slightly different, due to hydrolysis - in the solution of 1M $Na_3PO_4$ about 30% of $PO_4^3^+$ is protonated to $HPO_4^2^+$ ions and the pH of the solution is 12.7 - as in 0.05M strong base solution. But dried out salt will be perfectly neutral.

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[GCT]

You're complicating things,

$$2HCl_{(aq)} + Ca(OH)_2_{(aq)} \longrightarrow CaCl_2_{(aq)} + 2H_2O_{(l)}$$

from this the OP should know what's going on