C4 Flashcards
What are acids?
Substances that form hydrogen ions (H+) when they dissolve in water
What are alkalis?
Bases that form hydroxide ions (OH-) when they dissolve in water
What is the pH?
the measure of the concentration of H+ ions in a solution
How can we measure pH?
- using an indicator (e.g. universal indicator)
- pH probe- always used to electronically measure the pH
Describe the relationship between pH and concentration
As the concentration gets higher the pH gets lower.
- each decrease of 1 on the pH scale = concentration x 10
eg. pH 3= 0.001, pH 4= 0.0001
Describe a reaction between an acid and alkali(in terms of their ions)
a neutralisation reactions=
H+ + OH- → H20
What is the word equation for neutralisation reactions?
acid + alkali → salt + water
Give examples of common acids
- HCl = hydrochloric acid
- H2S04= sulphuric acid
- HNO3 = nitric acid
Describe the reaction between an acid and a metal
acid + metal → salt + hydrogen
Describe the reaction between an acid and metal oxide
acid + metal oxide → salt + water
Describe the reaction between an acid and a metal hydroxide
acid + metal hydroxide → salt + water
Describe the reaction between an acid and a metal carbonate
acid + metal carbonate → salt + water + carbon dioxide
Describe how to make a soluble salt
(Required practical)
- add dilute acid to a beaker
- gently heat it(Bunsen burner) and add the insoluble base gradually
- At first it will keep disappearing as it reacts but once the base stops disappearing it is in excess.
- Filter out the excess base using filter paper and a funnel
- With the salt solution, heat it in a water bath until around half of the water has evaporated
- Stop heating it and allow the rest of the solution to cool
- Filter the crystals out and then dry the crystals
Describe how to carry out a titration to find the volume of sodium hydroxide that reacts with 25.0cm3 of hydrochloric acid
- First, use a pipette to measure 25cm3 of hydrochloric acid and put it into the conical flask
- Add the indicator e.g. phenolphthalein , methyl orange and place the white tile underneath
- Fill the burette up until the 0 mark with sodium hydroxide and record the start volume of NaOH in the burette
- Gradually add sodium hydroxide to the conical beaker using the tap on the burette and swirl
- Once there is a permanent colour change, stop adding sodium hydroxide
- record the final volume of the sodium hydroxide in the burette and do final volume - initial volume to calculate the volume that was added
- Repeat the experiment, discount any anomalies and calculate a mean volume to improve the reliability of the results
What is the reactivity series?
Potassium
Sodium
Calcium
Magnesium
Carbon
Zinc
Iron
tin
lead
Hydrogen
Copper
Silver
Gold
Describe the reactions of the following metals with water
a)potassium
b)sodium
c)lithium
potassium ~ ignites instantly (sparks a lilac flame), the metal melts and floats, the metal moves very quickly on the surface of the water
sodium ~ sparks orange flame, travels speedily across the surface of the water, bubbles vigorously
lithium ~ turns pink in colour, bubbles and moves across the surface of the water
What does the reaction between a metal and water produce?
metal hydroxide + hydrogen
Describe the reactions of the following with acid
a) calcium
b)magnesium
c)zinc
d)iron
e)copper
• calcium has a violent reaction with rapid bubbling, hydrogen produced
• magnesium has bubbling, hydrogen produced
• zinc has slow bubbling, hydrogen produced
• iron has very slow bubbling
• copper has no reaction
What is a reduction reaction?
A reaction where oxygen is lost
A reaction where electrons are gained
What is an oxidation reaction?
A reaction where oxygen is gained
A reaction where electrons are lost
What does OIL RIG stand for?
Oxidation
Is
Loss(of electrons)
Reduction
Is
Gain(of electrons)
How are most metals found in the Earth?
As compounds- metal oxides
Why aren’t metals such as gold found as metal oxides?
They are very unreactive
How can metals less reactive than carbon be extracted?
a reduction reaction with carbon
Why is carbon used?
It’s cheap and abundant
What is used to extract metals that are more reactive than carbon?
Electrolysis
What is a redox reaction?
A reaction where reduction and oxidation occurs at the same time
What is a displacement reaction?
When a more reactive metal displaces (takes the place of) a less reactive metal
= a redox reaction
How do you write an ionic equation for Ca + FeSO4 → CaSO4 + Fe ?
- only show the particles that react and the products they form
- SO42- are spectator ions
- Ca + Fe2 + → Ca2 + Fe
What is electrolysis?
the breakdown of an ionic substance using electricity
What state must ionic compounds be in for electrolysis to be carried out?
molten or dissolved so electricity can be carried through
What is an electrolyte?
the liquid required to conduct electricity= molten or dissolved ionic substance
What is the name of the positive electrode and what does it attract?
Anode: attracts anions
What is the name of the negative electrode and what does it attract?
Cathode: attracts cations
During the electrolysis of molten ionic compounds, what happens at the cathode?
- the positively charged metal ion is attracted to the cathode
- the ion is then reduced- gains electrons to become an atom
- a thin layer of the metal is produced at the cathode
During the electrolysis of molten ionic compounds, what happens at the anode?
- negatively charged non-metal ions are attracted to the anode
- they are oxidised - lose electrons to become an atom
- typically a gas is produced e.g. chlorine- pair up because they are diatomic and bubbles of Cl2 are produced
Why would electrolysis be used?
When a metal is more reactive than carbon so it cannot be extracted by reaction with carbon
What are disadvantages of electrolysis?
- very expensive
- requires high amounts of energy
What ions are present in an aqueous solution of an ionic compound?
H+, OH-, metal +, non-metal -
What ion goes to the anode during the electrolysis of an aqueous solution?
- if a halide ion is present (group 7 ions), the halide ions go to the anode and halogen molecules are formed(diatomic and gas)
- if no halide ions are present, the OH- ions go to the anode and are discharged to form oxygen and water (4OH- → 2H2O + O2 + 4e-)
What ion goes to the cathode during the electrolysis of an aqueous solution?
- the least reactive element
- if metal is more reactive than hydrogen, H+ ions go to the cathode and are discharged to form hydrogen gas (2H+ + 2e- → H2)
- If less reactive, the metal ions go to the cathode and are discharged to form metal atoms(solid layer of metal)
