3b) Titrations, Energy And Chemical Tests

Question 0

How do you work out the concentration of a substance?

Answer 0

Number of moles = concentration x volume

Question 1

How are titrations used to find out concentrations?

Answer 1

Put some alkali with indicator in a flask
Add the acid using a burette
The indicator changes colour when all the alkali has been nutralised

Question 2

How do you work out the concentration in GRAMS?

Answer 2

No. Of moles = mass x relative formula mass

Question 3

Define endothermic

Answer 3

A reaction which takes in energy (heat) and creates a fall in temperature

Question 4

Define exothermic

Answer 4

A reaction which gives out energy (heat) with a rise in temperature

Question 5

What type of (endo/exothermic) reaction breaks bonds and why?

Answer 5

Endothermic
Energy must be supplied
Energy required > energy released

Question 6

What type of (endo/exothermic) reaction create bonds and why?

Answer 6

Exothermic
Energy must be released
Energy released > energy supplied

Question 7

How do you calculate fuel energy?

Answer 7

Calorimetry
Put 50g of water in the copper can
Record temperature
Weigh the spirit burner and lid
Put the spirit burner underneith the can and light it
Heat until the water reaches 50°c
Put out the flame
Measure the final temperature of the water
Weigh the burner and lid again

Question 8

Equation to calculate fuel energy

Answer 8

Energy transferred = mass of water x specific heat capacity of water (4.2) x temp change

Question 9

How to work out endo/exothermic from bond energy level graphs

Answer 9

Positive = endothermic - products are higher than reactants - energy taken in
Negative = exothermic - products are lower than reactants - height = heat given out - initial rise breaks bonds (activation energy)

Question 10

Why is activation energy lowered by catalysts?

Answer 10

Represents minimum energy needed to break bonds
Catalyst provides different pathway with lower activation energy - quicker
Overall change stays the same

Question 11

Bond energy caclulations

Answer 11

The breaking of one h-h molecule requires 436 and one Cl-Cl requires 242 =686kj
Forming two h-Cl releases 2x431 = 862kj
Overall more is released 862-678 =184kj
Energy is released = exothermic. So make it negative

= -184kJ/mol

Question 12

Pros and cons of using hydrogen in cars

Answer 12

Pro: very clean- product is just water
Con: needs special expensive engine. It needs another energy source. Very explosive and hard to store

Question 13

Pros and cons of the car industry developing fuel cells

Answer 13

Pros: adv. in cities as there’s no pollution
Stops dependence on crude oil
Con: not the end of power stations as we need fossil fuels: h is gas - harder to store than liquids; very explosive difficult to store; made from hydrocarbons (fossil fuels) or electrolysis (needs electricity)

Question 14

Flame test colours

Answer 14

Li - C(rimson)
So - Y(ellow)
Po - L(ilac)
Ca - R(ed)
Ba - G(reen)

Question 15

Coloured precipitates

Answer 15

Ca 2+ - white
Cu 2+ - blue
Fe 2+ - green
Fe 3+ - brown
Al3+ - white (colourless after dissolved in NaOH)
Mg2+ - white

Question 16

Test for carbonates

Answer 16

Acid + carbonates —> salt + water + carbon dioxide

Question 17

Test for halides and sulfates

Answer 17

Halide: Cl-, Br-, I- Add dilute nitric acid and silver nitrate
Cl - white precipitate
Br - cream precipitate
I - yellow precipitate

Sulfate: add dilute HCl and barrium chloride
White precipitate

Question 18

How many atoms is a mole?

Answer 18

6.023 x 10 ^ 23

Question 19

How do you calculate the amount of energy released by a chemical reaction?

Answer 19

Taking the temp. of reagents
Mixing in a polystyrene cup
Measure temp at end of reaction

Question 20

How can you reduce the amount of energy lost to the surroundings in a reaction?

Answer 20

Put it in a polystyrene cup into a beaker of cotton wool to give more insulation
Put lid on cup to reduce energy lost by evaporation

Question 21

How do cooling packs work?

Answer 21

Pack contains two compartments with different chemicals in
Snap partition so chemicals mix
Chemicals have an endothermic reaction and take in heat
Cools you down

Question 22

Why does calorimeter normally involve using a copper can?

Answer 22

copper conducts heat very well

Question 23

What does the height difference of the reactants and product show in an energy level diagram?

Answer 23

Energy taken in or given out in the reaction per mole

Question 24

How much is one calorie in joules?

Answer 24

4.2 joules = 1 calorie

Question 25

What is the specific heat capacity of water?

Answer 25

Amount of energy it takes to heat up 1g of water by 1oC

Question 26

What is activation energy?

Answer 26

Represents the minimum energy needed by reacting particles to break their bonds

Question 27

What does a catalyst do to a reaction?

Answer 27

Speeds up rate of reaction by lowering activation energy

BUT
Overall energy change stays the same

Question 28

What do hydrogen and oxygen produce when reacted?

Answer 28

Water

Question 29

Describe the reaction between hydrogen and oxygen

Answer 29

Exothermic
Releases energy
Negative energy change

Question 30

What is a fuel cell?

Answer 30

Electrical cell
supplied with a fuel and oxygen
Uses energy from the reaction to generate electricity

Question 31

How to test for halide ions?

Answer 31

Add dilute Nitric acid and silver nitrate solution
Cl - White precipitate of silver chloride
Br - Cream precipitate of silver bromide
I - Yellow precipitate of silver iodide

Question 32

How to test for sulfate ions

Answer 32

Add dilute HCL and barium chloride solution

Produces white per irate of barium sulfate