C5: Chemical Changes Flashcards
(27 cards)
What are the different sides of the pH scale?
The lower the pH, the more acidic it is
The higher the pH, the more alkaline it is
What is an acid?
An acid is a substance that forms aqueous solutions with a pH of less than 7.
Acids form H+ ions in water.
What is a base?
A base is a substance with a pH greater than 7.
What is an alkali?
A base that dissolves in water to form a solution with a pH greater than 7.
Alkalis form OH- ions in water.
What is the reaction between acids and bases called?
Neutralisation
acid + base —-> salt + water
The products are neutral
How to carry out a titration?
1) You want to find out the concentration of some alkali. Using a pipette and pipette filler, add a set volume of the alkali to a conical flask. Add two or three drops of indicator too.
2) Use a funnel to fill a burette with some acid of known concentration. Make sure you do this below eye level. Record the initial volume of the acid in the burette.
3) Using the burette, add the acid to the alkali a bit at a time - giving the conical flask a swirl. Go especially slowly when you think the end-point is about to be reached.
4) The indicator changes colour when all the alkali has been neutralised.
5) Record the final volume of acid in the burette, and use it, along with the initial reading, to calculate the volume of acid used to neutralise the alkali.
What kind of indicators do you use for titrations?
Single indicator, such as methyl orange (yellow in alkalis and red in acids).
What are strong acids?
They ionise completely in water.
All acid particles dissociate to release H+ ions.
What are weak acids?
They do not fully ionise in solution.
Only a small proportion of acid particles dissociate to release H+ ions
How does the pH scale work?
For every decrease of 1 on the pH scale, the concentration of H+ ions increases by a factor of 10.
Factor H+ ion concentration changes by = 10^-x (x is the difference in pH)
What is the products of an acid + metal oxide/ metal hydroxide?
Salt + water
The salt depends on the acid and the metal ion
What is the product of acid + metal carbonate?
Salt + Water + Carbon Dioxide
How does one create soluble salts using an insoluble base?
1) Get sulphuric acid and copper oxide.
2) Gently warm the dilute acid using a Bunsen Burner, then turn off the Bunsen Burner
3) Add the insoluble base to the acid a bit at a time, until no more reacts (the base is in excess). The excess solid will just sink to the bottom.
4) Filter out the excess solid to get the salt solution.
5) Gently heat the solution using a water bath to evaporate some of the water (to make it more concentrated) and then stop heating it and leave the solution to cool. Crystals of the salt should form, which can be filtered out of the solution then dried.
What is the reactivity series?
Lists metals in order of their reactivity towards other substances.
List the reactivity series from most reactive to least reactive?
Potassium
Sodium
Calcium
Magnesium
Aluminium
Carbon
Zinc
Iron
Tin
Lead
Hydrogen
Copper
Silver
Gold
Platinum
What do acid + metals make?
Salt + hydrogen
How is the speed of reaction indicated in acid + metal?
The rate at which the bubbles of hydrogen are given off.
What does metal + water make?
Metal hydroxide + hydrogen
What is the formation of a metal ore?
Oxidation = gain if oxygen
What is the formation of metal?
Reduction = loss of oxygen
How can metals be extracted?
Reduction using carbon
The ore is reduced and carbon gains oxygen so it is oxidised
What is oxidation and reduction in terms of electrons?
Oxidation = loss of electrons
Reduction = gain of electrons
What is the mnemonic?
OIL RIG
Oxidation Is Loss
Reduction Is Gain
Why is it called redox?
REDuction and OXidation happen at the same time.
