On which four factors does the rate of a reaction depend?
- Surface area of any solids
- Concentration (or pressure for gases)
What is the formula for measuring rate of reaction?
Rate of reaction = amount of reactant used OR amount of product formed ÷ time taken
Outline three methods by which the rate of a reaction can be measured.
- By observing a reaction of which the product is a precipitate and timing how long it takes to go cloudy
- By measuring the decrease in mass within a reaction that releases gas
- By measuring the amount of gas given off by a reaction
When the product of a reaction is a precipitate how can rate of reaction be measured?
By observing a mark beneath the transparent beaker where the reaction takes place, and taking note of the time it takes for the mark to totally disappear as the solution becomes increasingly cloudy.
Measuring the speed of a reaction that produces a ……. can be carried out on a mass ……… The quicker the reading on the ….. ….. drops, the faster the rate of reaction.
The volume of gas given off by a reaction can be measured by using a …….. ………, the more gas given off during a certain ……… interval, the faster the rate of reaction.
Measuring the speed of a reaction that produces a gas can be carried out on a mass balance The quicker the reading on the mass balance drops, the faster the rate of reaction.
The volume of gas given off by a reaction can be measured by using a gas syringe, the more gas given off during a certain time interval, the faster the rate of reaction.
Give one advantage and one disadvantage of using either a mass balance or gas syringe method to measure rate of reaction?
A - Most accurate equipment
D - gas is released straight into the room
A - Accurate to the nearest millilitre
D - if the reaction is too vigorous, the plunger can pop out of the syringe.
What is the reaction of hydrochloric acid and marble chips often used to demonstrate?
The effect of surface area on rate of reaction - the reaction wil be faster with smaller pieces of marble chips (or powdered chalk).
This can be demonstrated by using a gas syringe to measure the volume of Carbon Dioxide that is given off.
What is the reaction of magnesium metal with hydrochloric acid used to demonstrate?
How concentration affects rate of reaction. The greater the concentration of acid, the faster the reaction will be.
Sodium thiosulphate and hydrochloric acid are two chemicals, which are both ……. ……. that react together to form a ……… …………
A ……… ……… can be used to change the temperature at which this reaction takes place.
Sodium thiosulphate and hydrochloric acid are two chemicals, which are both clear solutions that react together to form a yellow precipitate (sulfur).
A water bath can be used to change the temperature at which this reaction takes place.
Which catalyst can be used in the decomposition of hydrogen peroxide? And which gas is given off by this reaction?
manganese (IV) oxide
Oxygen is given off, provifing an ideal way to measure the rate of reaction using the gas syringe method.
Which four factors increase the number of collisions in a reaction, and therefore increase the rate of reaction?
- Higher concentration
- Higher temperature
- Larger surface area
- More energy (eg. higher temperature)
Define the term ‘catalyst’
A catalyst is a substance that increases the rate of a reaction, without being changed or used up in said reaction.
List 3 disadvantages of using a catalyst in industry
- They can be expensive
- Most catalysts are very specialist and can therefore only be used for one specific reaction.
- Catalysts can be ‘poisoned’ by impurities and therefore stop working eg. sulfur impurities can poison the iron catalyst in the Haber process
What are the four main advantages of using a catalyst in industry?
- Increases the rate of reaction, product made faster
- Allows the reaction to work at a lower temperature, reduces the energy needed
- Reduces energy needed and therefore cost also
- They don’t get used up easily so can be used over and over again
What is an exothermic reaction?
An exothermic reaction is one which gives out energy to the surroundings, usually in a form of heat and shown by a rise in temperature.
List the 3 main examples of an exothermic reaction
- Burning fuels
- Neutralisation reactions
- Oxidation reactions
What is an endothermic reaction? Give one well known example
An endothermic reaction is one which takes in energy from the surroundings, usually in the form of heat and is indicated by a fall in temperature.
Thermal decomposition is an example of an endothermic reaction
How can reversible reactions be both endothermic and exothermic?
If a reaction is endothermic in one direction, it will be exothermic in the other direction. The energy absorbed in the endothermic direction will be equal to the energy given out in the exothermic direction.
What is the range of the pH scale?
0 to 14
Which pH indicates that a substance is:
a) an acid
c) an alkali
a) From 0 -6
c) From 8 - 14
What is a ‘base’? What is an ‘alkali’?
Base = A substance with a pH of greater than 7
Alkali - A base that dissolves in water
What do acids and alkalis form in water?
Acids create H+ ions in water
Alkalis form OH- ions in water
What is the reaction between acids and bases called? Give the word equation and also the equation in terms of H+ and OH- ions
acid + base ⇒ salt + water
H+(aq) + OH-(aq) ⇒ H2O(l)
When metals react with acids, what will be created?
acid + metal ⇒ a salt + hydrogen
Which metal does not react with dilute acids and why?
Copper does not react with dilute acids because it’s less reactive than hydrogen.
How can the presence of hydrogen be tested?
The burning splint/’squeaky pop’ test
What kind of salts do a) hydrochloric and b) sulfuric acid make when reacted with metals?
a) hydrochloric acid always makes chloride salts
b) sulfuric acid always produces sulfate salts
Nitric acid reacts with …… to produce …… but when reacted with metals it can produce …….. …….. instead.
Nitric acid reacts with alkalis to produce nitrates, but when reacted with metals it can produce nitrogen oxides instead.
Fill in the gaps:
Metal oxides and metal ……… are ………… Even bases that won’t ………. in water will react with acids, so all metal oxides and metal ………… react with ………. to form a ………. and water.
Metal oxides and metal hydroxides are bases. Even bases that won’t dissolve in water will react with acids, so all meta oxides and metal hydroxides react with acids to form a salt and water.
Finish these word equations:
hydrochloric acid + copper oxide ⇒ ……….. and …………
sulfuric acid + zinc hydroxide ⇒ ………. and ………..
nitric acid + magnesium oxide ⇒ ……….. and …….
hydrochloric acid + copper oxide ⇒ copper chloride and water
sulfuric acid + zinc hydroxide ⇒ zinc sulfate and water
nitric acid + magnesium oxide ⇒ magneisum nitrate and water
Fill in the gaps:
Ammonia dissolves in …… to make an ……. solution. When it reacts with nitric acid, you get a ……… salt - ……… ……….. There is no water produced.
Ammonia + Nitric acid ⇒ ……… ………
NH3(aq) + …… ⇒ NH4NO3(aq)
Ammonia dissolves in water to make an alkaline solution. When it reacts with nitric acid, you get a neutral salt - ammonium nitrate. There is no water produced.
ammonia + nitric acid ⇒ ammonium nitrate
NH3(aq) + HNO3(aq) ⇒ NH4NO3(aq)
Why is ammonium nitrate good fertiliser?
Plants need nitrogen to make proteins. Ammonium nitrate contains nitrogen from two sources - both the ammonia and nitric acid.
Most sulfates, nitrates and chlorides are soluble in water - what are the 3 main exceptions?
lead chloride, lead sulfate and silver chloride
How do you make a soluble salt using an alkali? (3 main steps)
- Exactly the right amount of alkali must be used to neutralise the acid, this can only be tested by using an indicator to show when the reaction has finished.
- Then it must be repeated with the same volumes of alkali/acid so that the salt isn’t contaminated with indicator.
- The water can be evaporated away to crystallise the salt.
If the salt you want to make is insoluble, what kind of reaction can you use?
Describe the process of making insoluble salts using a precipitation reaction
- You need to pick the two solutions that contain the ions you need eg. to make lead chloride tou need a solution with lead and chloride ions (lead nitrate, sodium chloride)
- Once the salt has precipitated out (and is lying at the bottom of the flask), you have to filter it from the soultion, wash it and dry it.
Give 3 ways precipitation reactions can be used to benefit us
- To remove poisionous ions from drinking water (eg. lead)
- To remove calcium and magnesium ions from water (to make it soft)
- To treat effluent (sewage), unwanted ions can be removed
What is the liquid used in electrolysis known as?
What is a cathode?
What is an anode?
A cathode is a negatively charged electrode
An anode is a positively charged electrode
Describe how electrolysis works (3 main steps):
- If you pass an electrical current through an ionic substance (that’s molten or in a solution), the elements that the substance is made of will break away from each other.
- Positive ions in the substance will be attracted to the cathode, here they will gain electrons. Negative ions are attracted to the anode, here they will lose electrons.
- When these ions gain/lose electrons they become atoms/molecules and are released.
What is oxidation? What is reduction?
Oxidation is the gain of oxygen, and loss of electrons
Reduction is the loss of oxygen and gain of electrons.
Oxidation Is Loss (of electrons)
Reduction Is Gain (of electrons)
In the electrolysis of lead bromide, which products are formed and at which electrodes?
At the cathode, one lead ion accepts two electrons to become one lead atom.
At the anode, two bromise ions lose one electron each to become one bromine molecule.
How does reactivity affect the products formed by electrolysis?
Sometimes there are more than two free ions in the electrolyte (eg. if salt is dissolved in water there will be H+ and OH- ions)
At the cathode, if metal ions and H+ ions are present, the metal ions will stay in solutionif the metal is more reactive than hydrogen because the more reactive an element is, the more likely it is to stay in ionic form.
So, hydrogen will be produced unless the metal is less reactive than hydrogen. Similarly, at the anode is OH- and halide ions are present then molecules or chlorine/bromine/iodine will be formed. If no halide is present then oxygen will be released.
When sodium chloride is dissolved in water and electrolysed, what three products are produced?
hydrogen, chlorine and sodium hydroxide
Draw a labelled diagram for the electrolysis of molten/dissolved sodium chloride
What happens at the cathode and anode in the electrolysis of sodium chloride?
At the cathode: two hydrogen ions accept two electrons to become a hydrogen molecule
At the anode: two chloride ions lose their electrons and become one chlorine molecule
What happens to the sodium during the electrolysis of sodium chloride?
The sodium ions stay in the solution because they’re more reactive than hydrogen. Hydroxide ions from the water are also left behind, meaning sodium hydroxide is formed in the solution.
Give the half equations for the electrolysis of sodium chloride
At the cathode: 2H+ + 2e ⇒ H2
At the anode: 2Cl- - 2e ⇒ Cl2
How are the products of the electrolysis of sodium chloride useful?
Chlorine has many uses eg. in the production of bleach and plastics
Sodium Hydroxide is a strong alkali and is used widely in the chemical industry eg. to make soap
What is the main ore of aluminium?
After mining and purifying bauxite, a white powder is left, what is this substance?
Pure almunium oxide Al2O3
Describe how electrolysis separates aluminium from alumnium oxide
- Aluminium oxide is dissolved in molten cryolite.
- Electrodes made of carbon (graphite) are used to electrolyse the substance.
- Aluminium forms at the cathode and oxygen at the anode.
- The oxygen then reacts with the carbon to produce carbon dioxide, meaning the positive electrodes gradually erode away.
Why is molten cryolite used in the electrolysis of aluminium oxide?
Al2O3 has a very high melting point, at 2000°C. Dissolving it in molten cryolite brings the melting point down to about 900°C, meaning less energy is used and it’s cheaper.
Give the half equations for the electrolysis of aluminium oxide
Cathode: Al3+ + 3e- ⇒ Al
Anode: 2O2- ⇒ O2 + 4e-
Outline the process of electroplating by electrolysis
- The negative electrode is the metal object you want to plate, and the positive electrode is the pure metal you want it to be plated with.
- The elctrolyte must contain ions of the plating metal.
- The ions that plate the metal object come from the solution, whilst the positive electrode maintains the ions in the solution.
What are the two main uses of electroplating?
Decoration: It’s cheaper to plate an object with a precious metal than to make it of that metal solidly.
Conduction: eg. copper conducts well, often used to plate metals for electronic circuits.