Flashcards in C5 Separate Chemistry 1 Deck (17):
Most metals are ___________ metals
Properties of transition metals?
High melting point
Oxidation of metals results in
What are the two ways of preventing rust?
The barrier method and the sacrificial method
Explain how the barrier method prevents rusting
Painting/coating with plastic/oiling/greasing
All work by preventing water and oxygen from reaching the iron
Explain the sacrificial method
More reactive metal than iron – the water and oxygen react with this sacrificial metal instead of with the iron
What is galvanisation?
An object can be galvanised by spraying it with a coating of zinc. Zinc layer is firstly protective, but if it is scratched, the zinc around the site of the scratch works as a sacrificial metal
Galvanisation is protection + sacrificial
How does electroplating improve the appearance and/ or the resistance to corrosion
Uses electrolysis to reduce metal ions onto an iron electrode. It can be used to cut the iron with a layer of a different metal that won't be corroded away
Why are alloys stronger than pure metals?
In pure metals atoms are all the same and so the layers can slide over each other
In alloys the atoms are of different sizes, there is no sliding and so they are stronger
Why is iron alloyed with other metals to produce alloy steels?
-carbon is addd to iron to make steel
-this is done because iron is too soft for some things e.g. Drill bits
- steel is inflexible, strong, corrosion resistant and harder
Explain how to go from mol/dm^3 --> g/dm^3
1. Work it out in mol/dm^3 (DO # of MOL DIVIDED BY VOLUME)
2. Convert into grams by using:
Mass in grams = mol x Mr
Explain how to conduct a titration
1. Add set volume of alkali to a conical flask (and 3 drops of indicator)
2. Fill burette with an acid with a known concentration , record volume
3. Add acid to alkali bit by bit (swirling constantly)
4. INDICATOR COLOUR CHANGE
5. Record final volume, calculate the volume of acid used to neutralise the alkali
State the colour changes to look for with the 3 indicators
ACID TO ALKALI
Litmus: pink to purple
Methyl orange: pink to yellow
Phenolphthalein: colourless to pink
Explain how to improve the accuracy of the titration
Do you a rough titration to get an approximate idea of where the solution changes colour
Then repeat the whole thing a few times making sure you get same answer each time within 0.10 cm^3. CONCORDANT RESULTS
Finally calculate the mean of your results ignoring any anomalies
Why is universal indicator not appropriate for titrations?
It is used to estimate the pH of the solution because it content variety of colours each colour indicates a change of PH
But during a titration between and alkali and acid you want to see A certain colour change at the end point so you need to use a single indicator
What is the formula for percentage yield?
Percentage yield = mass of actual yield/mass of theoretic yield
Then multiply answer by 100 to get a percentage