Coffee Lab Chemisty Lab

Question

I dont get it my professor asked

me to perform coffeelab experiment in chem collective:

“I dont understand how to get the answer.

 An eccentric chemistry professor (not mentioning any names) stops in every day and orders 200ml of Sumatran coffee at precisely 65.0°C. You then need to add enough milk at 5.00°C to drop the temperature of the coffee, initially at 95.0°C, to the ordered temperature.

Calculate the amount of milk (in ml) you must add to reach this temperature. Show all your work in the provided spaces.

In order to simplify the calculations, you will start by assuming that milk and coffee have the specific heat and density as if water. In the following parts, you will remove these simplifications. Solve now this problem assuming the density is 1.000 g/ml for milk and coffee and their specific heat capacity is 4.184 J/(g ºC).”

but added these procedures:

1. From the glassware section of the stockroom, drag a 600-mL beaker to the workbench.
2. From the solutions section of the stockroom, transfer the coffee to the workbench.
3. Transfer 250-mL of coffee to the 600-mL beaker.
4. Right click on the beaker containing the coffee and click on Thermal Properties. Check on the “Insulated from Surroundings” and set the temperature to 90°
5. Get milk from the stockroom. Same with the coffee, insulate the milk and set its temperature to 10°
6. Transfer the necessary amount of milk to the coffee to make the final temperature of the latte be 75°C.

Answer 1

We use a mass balance and an energy balance

m_c + m_m = (200 ml)(1g/ml) = 200 (g) (we've assumed the densities are equal and volume add)

m_cC_c(T_ci-T_f) = m_wC_w(T_f-T_wi) assuming all the heat leaving the coffee enters the water

So there are 2 equation and 2 unknowns (m_w and m_c) and if we assume C_c=C_w= 4.184 J/gK, this is solvable.

As far as the simulation is concerned... 1) You set it up. There is a discrepancy in the initial temperature of the water. 5° or 10°? 2) You vary the mass of the water and the mass of the coffee (200 - m_w) until you get the 65° desired as T_final.