Find initial temp. of alcohol when copper and aluminum are added

[nlingraham]

*Messed up title, should have been find initial temp of copper*

Homework Statement

8.00 g of aluminum at 200 °C and 18.0 g of copper are dropped into 50.0 cm³ of ethyl alcohol at 15 °C. The temperature quickly comes to 26.0 °C. What was the initial temperature of the copper?

Density of ethyl alcohol = .789 g/ml

mass of ethyl alcohol = 39.45 g, .03495 kg

mass of copper = .018 kg

mass of aluminum = .008 kg

T_f = 299 K

T_{i, alum} = 473 K

T_{i, eth} = 288 K

c for aluminum = 900 J/kg*k

c for ethyl alcohol = 2400 J/kg*k

c for copper = 385 J/kg*k

Homework Equations

Q_a + Q_c + Q_e = m_ac_aΔT + m_ec_eΔT + m_cc_cΔT = 0

The Attempt at a Solution

Q_a + Q_c + Q_e = m_ac_aΔT + m_ec_eΔT + m_cc_cΔT = 0

=(.008)(900)(-174) + (.03945)(2400)(11) + (.018)(385)(299-Ti) = 0

Ti = 268.51 K or -4.5 °C

That's what I did, but it says not quite and tells to check for rounding errors. However, I didn't round anything until the very end, so I'm not quite sure where I went wrong. I also tried -4.494 but that was wrong too.

 

[TSny]

mass of ethyl alcohol = 39.45 g, .03495 kg

Could this be the error?

 

[nlingraham]

Well, I feel stupid now. thanks.

 

[TSny]

No need to worry. We all make slips like that. Hope it works out now.