Antacid equation
Mg(OH)2 + 2HCl ➞ MgCl2 + 2H2O
Titration equation
NaOH + HCl ➞ NaCl + H2O
Group 2 trend in atomic radius
Increases down group - extra electrons shells down group
Group 2 trend in ionisation energy
Decreases down group - more shielding, distance from outer shell to nucleus
Reactivity of Group 2
Increases down group - easier it is to lose electrons, more reactive the element
Trend in melting point in Group 2
- **Decreases **except for Mg
- Metallic ions get bigger
- # of delocalised electrons same but further away from nucleus
- Reduced attraction betwen nucleus + sea of delocalised electrons
Trend in solubility down Group 2
- OH- hydroxide ions increase (single - charge)
- SO42- sulfate ions decrease (double - charge)
% atom economy
( mass of useful products / mass of all reactants ) x 100
Apparatus error
( 100 x margin of error ) / quantity measured
% yield
( actual yield / theoretical yield ) x 100
Why use a conical flask rather than a beaker?
Easier to swirl without spilling its contents
Why doesn’t the Mr need to be exact to get the molecular formula from the empirical?
Because the molecular formula will be a whole number multiple of the empirical fomula
Why do you need to note down temp. and pressure?
Because the volume of a gas depends on pressure and temperature
Potential errors in using a gas syringe?
- Gas escapes before bung is inserted
- Syringe sticks
- Some gases are soluble in water so true amount not measured (eg SO2 or CO2)
Experimental error %
100 x (real answer - experimental answer) / real answer
Experimental error > Apparatus error
Results deemed to be inaccurate
- Discrepancy
- Result due to other errors
Why do we need concordant results?
So we can say results are accurate and reproducaible and titration technique is good/consistent
Why is distilled water used to wash the sides of the flask?
- To ensure all acid on the side is washed into reaction mixture
- Water doesn’t react with reagents of change number of moles
Why is Mg(OH)2 suitable for dealing with excess stomach acid?
- Low solubility in water
- Not corrosive as it is a weak alkaline
- Doesn’t produce CO2 gas (which can cause wind)
How can you decrease sensitivity error?
- Increase size of measuremenet made
- Use apparatus with a greater resolution
How can you reduce error in a burette reading?
Increase titre volume by:
- increasing vol. and conc. of substance in flask
- decreasing conc. of substance in burette
How can you reduce error in measuring mass?
Weighing sample before and after addition, then calculating the difference
Why should we fill the jet space in the burette?
May lead to a larger than expected tire reading
Experimental error (% diff. between actual and calculated value) < Apparatus error
- All errors can be explained by sensitivity of equipment
- No discrepancy
