Chemistry b Flashcards
How is ‘a mole’ significant in chemistry ?
When you have that precise number of carbon-12 atoms it will weigh 12g. It works for every element (Ar) or compound (Mr)
What is ‘a mole’ ?
It is the name given to the number:
602,300,000,000,000,000,000,000
What is concentration ?
A measure of how crowded things are
What is concentration measured in ?
Moles per dm^3
(^3 = cubed)
Or Grams per dm^3
What are titrations ?
They allow you to find out exactly how much acid is needed to neutralise a quantity of alkali
What indicators are used in titrations ?
- Phenolphthalein - alkali=pink acid=colourless
* Methyl Orange - alkalis=yellow acid=red
Why is universal indicator not used ?
It changes colour gradually, but we need definite colour change.
Explain the process of a titration experiment
Put some alkali in a flask with indicator. Gradually add the acid a bit at a time using the burette. The indicator will change as it becomes neutralised. Record the amount of acid used using the marks along the burette.
1 dm^3 is equal to what ?
1000cm^3 or a litre
See revision guide for titration calculations
Page 88
How can you measure energy transfer ?
By taking the temperature at the start and at the end of the reaction. The difference gives us the amount of energy transferred
What is biggest problem with energy measurements ?
Some of the energy will be loft to the surroundings
How can you reduce heat lost to the surroundings when measuring heat exchange ?
- Insulate the equipment holding the liquid
* Put a lid on to reduce heat loss through evaporation
What is an exothermic reaction ?
A reaction which GIVES OUT energy to the surroundings, usually in the form of heat and shown by a RISE in temperature
What is an endothermic reaction ?
A reaction which TAKES IN energy from the surroundings, usually in the form of heat and shown by a FALL in temperature
What happens during a chemical reaction ?
Old bonds are broken and new bonds are formed
Is breaking bonds an endothermic reaction ?
Yes. Energy must be supplied to break existing bonds, so energy is TAKEN IN by the surroundings.
If energy is released to form bonds, what type of reaction is it ?
Exothermic
If the reaction is endothermic overall, what does this tell us ?
The energy required to break old bonds is greater than the energy released when new bonds are formed.
What is calorimetry ?
Different fuels have different amounts of energy. To measure the amount of energy released when a fuel is burnt, you can simply use the flame to heat up water. This is known as calorimetry
What equation will tell you the energy transferred by different fuels ?
Energy transferred = mass of water x specific heat capacity of water x temperature change
What is the unit energy change is recorded in ?
Joules
Why is the energy transfer figure usually lower than the real energy transferred ?
Because a lot of energy is wasted heating the container or the air around the container