Posted by Ryan on .
If you have 320.0 mL of water at 25.00 °C and add 110.0 mL of water at 95.00 °C, what is the final temperature of the mixture? Use 1.00 g/mL as the density of water.

Chemistry 
Steve,
Because you're just mixing water, the specific heat is the same for both liquids. So, it's just like adding a bunch of weighted numbers:
(320*25 + 110*95)/(320+110) = 42.91°C
You can use a fancy formula incorporating the specific heats, but they all cancel out in the end, since they're the same.
As a ballpark check, the average of 25 and 95 is 60°C, but you have more cool water than hot, so the result will be below the average. 
Chemistry 
Henry,
Here's a little variation of this one:
"If you combine 310.0 mL of water at 25.00 °C and 100.0 mL of water at 95.00 °C, what is the final temperature of the mixture? Use 1.00 g/mL as the density of water."
ANS: 42.07 Degrees 
Chemistry 
Sarah,
If you combine 310.0 mL of water at 25.00 °C and 140.0 mL of water at 95.00 °C, what is the final temperature of the mixture? Use 1.00 g/mL as the density of water.