Topic 4-Chemical Changes Flashcards
How do you measure a pH of a solution?
An indicator is a dye that changes colour depending on whether its above or below a certain pH. It will gradually change colours over a broad range of pH. These are wide range indicators and they are useful for estimating pH.
A pH probe attached to a pH meter can measure pH electronically. The probe is placed in the solution you are measuring and the pH is given as a numerical value meaning it is more accurate than an indicator.
What happens to acids in aqueous solutions?
They ionise to produce hydrogen ions.
What happers to strong acids in water?
Such as hydrochloric acid ionise completely in water. All the acid particles dissociate to releass hydrogen ions.
What happens to weak acids in water?
They dont fully ionise so only a small proportion of acid particles dissociate to release hydrogen ions. The ionisation of a weak acid is a reversible reaction.
What is the pH a measure of?
The concentration
of hydrogen ions in the solution.
What does the concentration of an acid tell you?
How much acid there is in a certain volume of water.
What does acid strength tell you?
It tells you what proportion of the acid molecules ionise in water.
Describe the practical of making a salt from an insoluable base?
To make copper chloride you could mix hydrochloric acid and copper oxide.
Gently warm the dilute acid using a bunsen burner.
Add the copper oxide to the hydrochloric acid abit at a time until no more reacts. You will know it has been neutralised as even after stirring the excess solid would just sink to the bottom of the flask.
Then filter out the excess solid to get the salt solution.
To get the crystals of the salt gently heat the solution using a water bath or electric hester to evaporate some of the water then stop hesring and leave it to cool. Crystals of the salt should form which can be filtered out of the solution and the dried. (Crystallisation).
What is the order of the reactivity series?
Potassium Sodium Lithium Calciun Magesium Carbon Zinc Iron Hydrogen Copper
Why are carbon and hydrogen in the reactivity series?
Metals less reactive than carbon can be extracted from there ores by reduction with carbon. Metals more reactive cant be extracted this way.
Metals more reactive than hydrogen will react with acids. Metals less reactive will not react with acids.
How can you indicate the speed of a reaction?
The rate that hydrogen bubbles are given off.
What metals will react with water?
Potassium
Sodium
Lithium
Calcium
What metals wont react with wated?
Zinc
Iron
Copper
What is the formation of a metal ore called?
Oxidation. There is a gain of oxygen.
What is the extraction of a metal called?
Reduction. There is a loss of oxygen.
How can metals be extracted using carbon?
Metals above carbon have to be extracted using electrolysis.
Metals below carbon in the reactivity series can be extracted by reduction using carbon.
For example iron oxide is reduced in a blast furnace to make iron. This is because carbon can only take oxygen away from metals which are less reactive than carbon itself.
