Pràctica Fisica Del Laboratori

TOPIC LAB ACTIVITY 4
Heats of reaction (exothermic or endothermic reactions)
Objectives
Some reactions give out heat and others take in heat. In exothermic reactions the temperature goes up, inendothermic reactions the temperature goes down. In this experiment, various reactions are examined. Temperatures are measured to decide whether a particular reaction is exothermic or endothermic.Material
Test-tube
Spatula
Citric acid
Hydrogen carbonate
Copper (II) sulfate
Powdered zinc
Thermometer
Beaker
Pipette

Safety
Wear eye protection.
Anhydrous copper (II) sulfate isharmful.
Zinc powder is flammable.

Procedures
Experiment 1:
1. In a dry test-tube mix one spatula measure of citric acid and one spatula measure of sodium hydrogen carbonate.
2. Put 2 cm³ of water inanother test tube.
3. Record the temperature of the water.
4. Add the mixture to the water.
5. Watch what happens and take the temperature of the solution.

Experiment 2:
1. Put about 5 cm³ ofcopper (II) sulfate solution in a test-tube.
2. Record the temperature.
3. Add a spatula measure of powdered zinc.
4. Record the new temperature.

Results
What to record
What was done and anychanges in temperature from the starting temperature of your reaction. A table may be useful.
Initial solution | Temp. of solution/ °C | Solid added | Final temp. of mixture / °C | Temperaturechange | Type of reaction |
1 | 16° | Acid citricHydrogen carbonate | 8° | 8° | Endothermic |
2 | 16° | Copper (II) sulfate | 20° | 4° | Exothermic |

Questions
1. Which reactions are exothermicand which are endothermic?
- Experiment 1: The reaction is endothermic.
- Experiment 2: The reaction is exothermic.
2. Write word and symbol equation for Experiment 2.
Copper(II) sulfate --->CuSO 4
Zinc ---> Zn
Zn(s) + CuSO4(aq) ---> ZnSO4(aq) + Cu(s)
3. Which two substance could be put in a cold pack?
Could be put in a cold pack substance: Experiment 1.
Because the...