Flashcards in Chemistry 2 Deck (100):
What is a compound?
A substance that's formed when two or more elements chemically combine.
Structure of ionic compounds.
Giant structures made of ions. Held in a lattice. Strong forces of electrostatic attraction between the ions which acts in all directions.
What are simple molecules?
Molecules made up of a few atoms.
Structure of metals.
Giant structure. Atoms are arranged in a regular pattern.
What are giant structures?
Structures which have a lot of atoms. An example is metals.
What is the bonding in metals?
Electrons on the outer shell are delocalised. They are free to move about the whole structure. There are strong forces of electrostatic attraction between positive metal ions and negative electrons, it is this force that helps to keep the structure together.
What are delocalised electrons?
Aren't associated with a particular atom or bond.
Do ionic compounds have a low or high melting and boiling point?
High, as a result of the strong forces of electrostatic attraction between the ions. It requires a lot of energy to overcome these forces. When ionic compounds melt the ions can move freely and carry a current.
Do ionic dissolve in water?
Yes, the ions separate and are free to move so they can carry a current.
What are the properties of simple molecules?
Low melting and boiling points.
Mostly gases or liquids at room temperature.
Don't conduct electricity as there are no free ions or electrons.
What is the bonding in simple molecular substances?
Atoms form very strong covalent bonds but the intermolecular forces between these molecules are weak.
Give three examples of giant covalent structures/ macromolecules.
What are giant covalent structures?
All atoms are bonded to each other by strong covalent bonds. A lot of energy is required to overcome these bonds so therefore the have a high melting and boiling point.
What is the difference between giant covalent structures and giant ionic structures?
Giant covalent structures don't have charged ions.
Each carbon atom forms four covalent bonds in a rigid structure.
Each carbon atom forms three covalent bonds. This creates layers which are free to move over each other as there are no covalent bonds between them. Due to this graphite is soft and slippery.
Layers in graphite.
The layers are held by weak intermolecular forces. These are easily overcome so they can slide over each other. There are also delocalised electrons which are free to move throughout the structure. This make graphite a good conductor of heat and electricity.
What are the properties of metals?
They are malleable as atoms can slide over each other.
They can conduct heat and electricity due to the delocalised electrons.
Why are alloys harder than pure metals?
1) Different elements have different sizes atoms.
2) When a metal is mixed with a pure metal, the layers of atoms will be distorted.
3) This means the layers will find it difficult to slide over each other.
4) This makes alloys harder than pure metals.
What are shape memory alloys?
A type of smart material which can change their shape. But when heated they turn back into their original shape.
What are smart materials?
Behave differently depending on the conditions.
How big are nanoparticles?
1-100 nanometers across. They contain a few hundred atoms.
What are fullerenes?
Type of nanoparticle. They are carbon atoms which are arranged in hexagonal rings.
What are the uses of fullerenes?
Medicine- they are absorbed easily by the body so they could be used to deliver medicine to the cells of the body where it is needed.
Can be joined together to make nanotubes.
What are polymers?
Large molecules formed when small molecules/ monomers join together. Strong covalent bonds hold the atoms together.
What are thermosoftening polymers?
Made of tangled chains of polymers.
What are thermosetting polymers?
Have cross-links between polymer chains. This means that it doesn't melt and instead it burns.
In thermosoftening polymers, what are the chains held together by?
What effects the properties of polymers?
What is low density polyethene?
Made by heating ethene to 200 degrees under a high pressure. It is flexible and used for bags.
What is high density polyethene?
Made at a lower temperature and pressure. It's rigid and used for drainpipes.
What is the atomic number?
Number of protons.
What is the mass number?
Number of protons and neutrons.
What is an isotope?
Different forms of the same element which have the same number of protons and a different number of neutrons.
What is the relative atomic mass?
The mass number.
What does the relative atomic mass tell you?
How heavy the atoms of an element are compared to the atoms of carbon 12.
How do you calculate the Mr of a compound?
Add the relative atomic masses together.
How do you calculate the number of moles?
How do you work out the percentage mass?
Ar x Number of atoms/ Mr
How do you work out the empirical formula?
Write percentages given in the question.
Then write Ar.
Divide by smallest answer given above.
How do you calculate the mass of a product?
Write out balanced equation.
Divide and then multiply.
What is the percentage yield?
Amount of product you get from a reaction.
How do you calculate the percentage yield?
Actual yield/ Predicted yield x 100.
Why are percentage yields never 100%?
Reaction is reversible- The reactants will never be completely converted to products as the reaction goes both ways.
Unexpected reactions may have taken place- This means there may not be enough reactant to make the product.
Product is lost when its separated from the reactants- Some product may be lost when its separated from from the reaction mixture.
How can industrial methods be sustainable?
Use reactions with high percentage yields, otherwise you waste a lot of chemicals and use up a lot of resources.
Use reactions that don't need much energy.
Use materials which have come fro, renewable resources.
What are the stages of paper chromatography?
Put food in cup and add solvant.
Put a spot of the solution on a pencil baseline.
Put the filter paper in some solvent but the baseline must be above the solvent.
What is the study of nanoparticles known as?
Why should you use a pencil for a baseline?
A pen could dissolve and confuse the experiment.
What is a chromatogram?
The piece of paper you get at the end which has the separated spots on.
What does three spots mean?
At least three dyes.
What are the three advantages of instrumental methods?
How does gas chromatography work?
A gas is used to transport a mixture of substances through a column which is packed with solid material.
As the substances travel at different speeds, they separate.
The time taken to reach the detector is known as the retention time which can help identify the substance.
The recorder draws a gas chromatogram.
What does the number of peaks on a gas chromatogram show?
Number of substances.
Why would a mass spectrometer be used?
It can detect small quantities. And it tells you the relative molecular mass of each substance.
What are the four factors that effect the rate of a reaction?
Temperature, concentration, surface area, catalysts.
How can you increase the rate of a reaction?
Increase the energy of collisions between particles so more successful collisions take place.
Increase the number of collisions which occur so that the probability of the successful collisions increases.
Define activation energy.
The minimum amount of energy required by particles to react.
What are the advantages of catalysts?
Save money as the reaction can work at a lower temperature.
Never get used up so they can be reused many times.
What are the disadvantages of catalysts?
Stop working with impurities.
High initial cost.
Different reactions require different catalysts so you have to buy more than one which can cost a lot.
How do you calculate the rate of reaction?
Amount of reactant used or product formed/ Time.
What is a precipitate?
A solid formed in a solution during a chemical reaction.
What experiment is best for a see-through solution?
Precipitation. You time how long it takes for a mark to disappear as a precipitate forms, which causes the solution to go cloudy.
What is the best way to accurately measure the rate of reaction?
Change in mass. You can easily measure the gas released using a balance.
What is the best way to measure the rate of reaction if the gas given off is poisonous?
Volume of gas given off. Uses a gas syringe which measures the gas given off.
Hydrochloric acid and marble chip experiment.
Marble is a form of calcium carbonate which will react with dilute hydrochloric acid. As the reaction produces carbon dioxide gas, you can find out the rate of reaction by measuring the volume of gas produced. This can be used to find out the effect of surface area so you can repeat the experiment however using smaller pieces of marble each time.
Magnesium metal and hydrochloric acid experiment.
The reaction gives off hydrogen gas, so you can measure the rate of reaction by measuring the loss in mass using a balance. This can be used to see how concentration effects the rate of reaction as the acid can be used with different concentrations.
Sodium thiosulfate and hydrochloric acid experiment.
They are both clear solutions so the experiment involves watching a mark dissonance through cloudy sulphur. This reaction can be repeated for solutions at different temperatures and therefore it can be used to see the effect of temperature on the rate of reaction.
Decomposition of hydrogen peroxide.
Shows the effect of a catalyst on the rate of reaction. This reaction tends to be slow so manganese oxide catalyst is used to speed the reaction up and potato peel can also be used. As one of the products is oxygen gas, the rate of reaction can be measured by the syringe method.
What happens to energy during a chemical reaction?
It is transferred to and from the surroundings.
Give an example of a exothermic reaction.
Neutralisation and oxidation reactions.
Give an example of an endothermic reaction.
Give a use of exothermic reactions.
Hand warmers use the exothermic oxidation of iron in air to generate heat.
Give a use of endothermic reactions.
Injury pack which is used in sport. They take in heat and the pack becomes cold.
True or false.
All reversible reactions are exothermic in one way and endothermic in the other.
How can you test the pH?
Use an indicator such as universal indicator.
What ions do acids form when dissolve in water?
What ions do alkalis form when dissolved in water?
What is a neutralisation reaction?
When an acid reacts with a base to form a salt and water.
What is the general equation for a neutralisation reaction?
Acid + Base (goes to) Salt + Water.
What is the word equation for reacting metals with an acid?
Acid + Metal (goes to) Salt + Hydrogen.
Can all metals be used to make salts?
No, some are too reactive such as sodium. Also, some are not reactive enough such as copper.
Making salts from metal oxides and hydroxides, what is the word equation?
Acid + Metal oxide or metal hydroxide (goes to) Salt + Water.
Making salts from ammonia, what is the word equation?
Ammonia + Nitric acid (goes to) Ammonium nitrate.
This can be used as a fertiliser as they supply nitrogen which is essential for plants to make proteins.
Making soluble salts from metals or insoluble bases.
1) Put chosen acid in a beaker.
2) Add insoluble reactant and stir, as it reacts it will dissolve in the acid.
3) Continue adding he insoluble reactant until it is in excess.
4) Filter out excess insoluble reactant to get the salt solution.
Making soluble salts from alkalis.
In order to get a pure salt, you need to add the exact amount of alkali to naturalise the acid. To do this you use an indicator. Then repeat the experiment with the same volumes of alkali and acid to make sure that the salt isn't contaminated with the indicator.
When making a salt from a insoluble reactant or an alkali you are left with a solution. To make this a pure, solid crystal of salt, crystallisation occurs. To do this you heat the salt to evaporate most of the water which makes the solution more concentrated. Then you leave it to slowly evaporate at room temperature.
Making insoluble salts.
Use a precipitation reaction. You need to pick two aqueous solutions that contain ions which are needed and then you mix them together. Once it has been precipitated, you filter it, wash it and dry it on filter paper.
What is a use of precipitation reactions?
Can remove particular ions form solutions.
To do this you make an insoluble salt precipitate that contains the ion.
After separating the precipitate from the solution you can get rid of it which leaves a solution which doesn't contain the ions.
What are electrolytes?
A liquid to conduct electricity.
What is oxidation?
Loss of electrons.
What is reduction?
Gain of electrons.
What do half equations show?
The reactions at the electrodes.
Predicting the products of electrolysis.
At the negative electrode-
If metal ions and H+ ions are present, it will stay in the solution if it is more reactive than hydrogen.
At the positive electrode-
If OH- and halide ions are present then molecules of bromine, iodine and chlorine will be formed. If no halide is present, oxygen will form instead.
Sodium chloride electrolysis.
It produces hydrogen, chlorine and sodium hydroxide.
At the negative electrode-
Positive hydrogen ions get attracted as they are opposite. They gain an electron and combine to form hydrogen molecules. This is reduction. It causes hydrogen to be released at the negative electrode.
Half equation= 2H+ + 2e- (goes to) H2
At the positive electrode-
Negative chlorine ions get attracted as they are opposite. They lose an electron and combine to form chlorine molecules. This is oxidation. It causes chlorine to be released at the positive electrode.
Half equation= 2Cl- -2e- (goes to) Cl2
Sodium ions remain as they are more reactive than hydrogen.
Hydroxide ions from the water remain.
This leaves sodium hydroxide.
Extracting aluminium by electrolysis.
Aluminium oxide has a high melting point of over 2000 degrees and melting it would cost a lot. Therefore, it is dissolved in molten cryolite which brings the melting temperature to around 900 degrees. This make the process cheaper and therefore saves a lot of money.
The electrodes are made of carbon which is a good conductor of electricity. At the negative electrode aluminium forms and at the positive electrode oxygen forms. The oxygen then reacts with the carbon to produce carbon dioxide. This means that over time the electrodes get eaten away and as a result they will need to be replaced.
Negative= Al3+ + 3e- (goes to) Al
Positive= 2O2- (goes to) O2 + 4e-
What is electroplating?
Uses electrolysis to coat the surface of one metal with another metal.
The negative electrode is the object you want to plate.
The positive electrode is the pure metal in which you want it plated with.
There needs to be an electrolyte which contains the ions of the plating metal. This is because they will cover the metal you want to plate. The ions are replaced by the positive ions from the positive electrode.
What are the uses of electroplating?
How can you make soluble salts?
Reacting metals with acids.
Reacting bases with acids.
Metal hydroxides and oxides.