RP4: Temperature Change Flashcards
What is the aim of this experiment?
- Investigate the variables that affect temp change in chemical reactions
How would you investigate the temp change when different volumes of NaOH are added to HCl?
1) use large measuring cylinder to put 30cm³ dilute hydrochloric acid into polystyrene cup
2) stand cup inside beaker to make it more stable
3) use thermometer to measure temperature of acid and record this
4) add 5cm³ sodium hydroxide solution into small measuring cylinder
5) pour sodium hydroxide into cup, quickly fit lid and gently stir solution with thermometer through hole. when reading on thermometer stops changing write temperature in the table
6) repeat steps 4 and 5 to add further 5cm³ of sodium hydroxide to cup until 40cm³ has been added. last few should produce temperature fall than rise
7) calculate mean maximum temperature for each volume of sodium hydroxide
8) plot a line graph of total volume of sodium hydroxide added in cm³ (x axis) against mean maximum temp in ºC (y axis).
9) draw two straight lines of best fit - one through points increasing and one through points decreasing. ensure the two lines are extended so they cross
List the different variables
- IV: volume of sodium hydroxide
- DV: maximum temperature change
- CV: volume of hydrochloric acid, concentrations of hydrochloric acid and sodium hydroxide solution
Why does temperature increase to begin with?
- initially, as the volume of sodium hydroxide solution increases, the maximum temperature reached increases because, when we add more particles of sodium hydroxide, they react with hydrochloric acid and release more energy as the reaction is exothermic
What happens to the temperature at a certain volume?
- the maximum temperature reached stops increasing no matter how much sodium hydroxide we add – at this point, the sodium hydroxide is in excess and the acid is now limiting the increase in the rate of reaction
Why does the temperature decrease slightly?
- because the volume of the whole solution is increasing so the energy is spread across a larger volume, so appears to be a lower temperature
List some safety precautions
Wear safety goggles.
If the reaction is exothermic, will the thermometer record an increase or decrease in temp?
- Increase in temp as energy is transferred to the surroundings
How could you reduce the amount of heat energy lost to the surroundings?
- Mix reactants in a polystyrene cup
- Play polystyrene cup in a beaker of cotton wool
- Lid on the cup to reduce energy lost by evaporation
When investigating the temp change between two chemicals, why should the chemicals both start at the same temp?
- So that their individual temps do not have an effect on the temp recorded once combined
How could you ensure that two reactants in separate test tubes were the same starting temp?
- Use a thermometer
- Place test tubes in a water bath
Why is important to stir the mixture when taking a temp reading
- To ensure the temp measure is consistent throughout the mixture
- Ensure reactants have fully reacted
How could the temp be measure more precisely and more reliably?
- More precise: Use a digital thermometer
- More reliable: Repeat experiment and calc mean temp
How could you test the effect of acid conc on the energy released in a neutralised reaction?
- Place both reactants in a water bath so they are the same temp, record initial temp
- Add alkali to the acid and record the final temp
- Calc temp change
- Repeat process using diff conc of acid
- Record results for each conc in a table
What must be controlled when testing the effect of acid conc in a neutralisation reaction?
- Alkali conc and volume
- Acid volume
- Initial temp of each reactant
- External temp
