Quantitative chemistrt Flashcards
How do you work out concentration?
Amount/volume
What is concentration measured in?
Mol/dm3
Hydrochloric acid is added to a strip of magnesium and a gas is released. Write the symbol equation for this.
HCl + Mg -> MgCl + H2
Mg= +2 ion Cl= -1 ion
HCl + Mg -> MgCl2 + H2
Balanced:
2HCl + Mg -> MgCl2 + H2
Relative formula mass of sulphuric acid
98
What is moles?
Unit for amount of a substance
How many atoms are there in a mole?
6x10 23
Equation for moles
Moles= Mass/mr
Hydrogen peroxide (H2O2) decomposes into water and oxygen. How much oxygen gas will be given off from 40.8g of hydrogen peroxide?
H2O2 -> H2O + O2
Balanced:
2H2O2 -> 2H2O + O2
Mr
2H2O= 68
2H2O= 36
O2=32
- 8 -> ?
- 8 -> 19.2
Titration method
Pipette 25.0 cm3 of alkali into a conical flask, add a phenolphthalein indicator
Fill a burette with an acid of known concentration
Take the initial reading on the burette and record it
While swirling the flask, use the tap to slowly add the acid into the alkali
When the first permanent colour change (Pink -> Clear) Stop adding acid
Record the final volume in the burette, calculate the volume of acid to neutralise alkali using initial volume.
Make sure results are within 0.10 cm3.
Work out mean ignoring anomalous results
Properties of a strong acid
Fully dissociate HCl -> H+ + Cl- Big difference between strength and concentration Hydrochloric Nitric Sulphuric
Properties of a weak acid
Partially dissociate
H2O reversible arrows H+ + OH-
True or false
Ionic Compounds have to be molten or dissolved to be able to conduct electrolysis
True
What is cryolite used for?
To reduce the melting point of molten aluminium
What is attracted to the cathode in aluminium electrolysis?
Al3 + 3e- -> Al
What is attracted to the anode in aluminium electrolysis?
2O2- 4e- -> O2
What element is the anode made of in aluminium electrolysis?
Carbon
What gas is released at the anode in aluminium electrolysis?
Oxygen
How is carbon dioxide produced in aluminium electrolysis?
The carbon anode reacts with the oxygen gas released
What are the common set ups for electrolysis?
Sodium Chloride: H2 Cl2 NaOH
Sodium Sulphate H2 O2
Copper chlorideCu Cl2
Copper sulphate Cu O2
What is the test for hydrogen gas?
Squeaky pop
What is the test for oxygen gas?
Relighting glowing splint
What is the test for chlorine?
Bleaches damp litmus paper
Percentage yield
Actual yield/ Theoretical yield
What you made/ How much you thought you would make
Atom economy
Mr of atoms in required products/ Mr reactants
Titration calculations
Calculate number of moles of acid used
Use this to find the number of H+ ions involved in reactions
Equal to number of OH- ions involved in the reaction
Calculate number of moles alkalised
Calculate the concentration of alkali
Number of moles= concentration x volume
Number of moles= mass/Mr
Example of titration calculation
25cm3 of NaOH was neutralised by 15cm3 of 0.2 mol/dm3 HCl, find the concentration of the alkali
Concentration alkali=X
Volume of alkali= 25cm3
Concentration acid= 0.2 mol/dm3
Volume of acid = 15cm3
Number of moles of acid= 0.2 x 0.015
=0.003
moles of alkali/volume= concentration
0.003/0.025 =0.12
How much does 1 mole take up?
24dm3
Electrolysis required practical
Aluminium extracted from ore bauxite by electrolysis. Bauxite contains aluminium oxide. Al2O3
Aluminium oxide has very high melting point, cryolite lowers melting point
Molten mixture contains free ions- conduct electricity
Positive Al3+ ions attracted to negative electrode where each pick up 3 electrons and turn into neutral aluminium atoms. Sink to bottom of electrolysis tank
Negative O2- ions attracted to positive electrode where lose 2 electrons. Neutral oxygen atoms combine to form O2 molecules.
What does the law of conservation state?
no atoms are lost or made during chemical reactions, so the mass of the products equals the mass of the reactants
