HCl(aq)+NaOH(aq) ? ?

Question

In my AP Chem class my teacher took two aqueous solutions, 2.0 M HCL and 2.0 M NaOH, each 500 mL. He mixed the both together and as they mixed heat was released and the beaker got hot. He showed us where the 1000 mL mark on the beaker was and the mixture was significantly higher. What exactly happened here?

Answer 1

What you witnessed was a very basic neutralization reaction.  When you mix an acid (HCl) and a base (NaOH), you make water and a salt.  In this case your salt was NaCl, which never really "forms" because both Na+ and OH- ions are very happy in water.  This particular reaction also releases energy as heat.

Regarding the "gain" in volume:  Complete bunk.  Beakers are far from accurate measuring devices, and the lines on them are thus far from accurate.  If he indeed added 500 mL of each chemical, then he ended up with 1000 mL of saltwater.  There is no way to gain volume magically.

Making water doesn't increase the volume.  You've only changed what's in the volume.  And expanding the liquid by a visible amount due to an increased temperature is wrong, too.  Try sticking a beaker of water on a hot plate and bringing it to a boil.  You will never see your volume "increase".  And nowhere near enough heat would have been generated here to do that, anyway.

Answer 2

dbacksjay2 is wrong

there is an increase in volume due to neutralization or strong acids and bases.

500mL of 2M HCl and 500 mL of 2M NaOH have more mass than 1L of H2O.  However, due to neutralization, total H2O mass is increased in product.  The acids and bases are strong, and therefore dissociate completely in H2O.  The ionic equation:

H+(aq) + Cl–(aq) + Na+(aq) + OH–(aq) --> Na+(aq) + Cl–(aq) + H2O

Therefore, according to V = m/D, an increase in mass (of H2O) results in an increase in volume.

next time you try to prove other ppl wrong, dbagjay2, learn your stuff.

Have a nice day sir.

Answer 3

The reaction is exothermic, meaning it generated heat.  As liquids are heated they expand.