Topic 4- Chemical Changes Flashcards

Question

What is an ion?

Answer 1

Ions are electrically charged particles formed when atoms lose or gain electrons.

Answer 2

All acids IONISE in aqueous solutions (they form H+ ions).

Answer 3

Strong refers to the degree to which an acid will ionise (form H+ ions). A strong acid is completely ionised in aqueous solution. strong acids are hydrochloric, nitric and sulfuric acids.

Answer 4

A weak acid is only partially ionised in aqueous solution. Examples of weak acids are ethanoic, citric and carbonic acids.

Answer 5

Weak acids only PARTIALLY ionise in water-if you put a sample of a weak acid in water, only some of the acid molecules will ionise and release H+ ions.

Answer 6

The ionisation of a WEAK acid is a REVERSIBLE REACTION, which sets up an EQUILIBRIUM between the UNDISSOCIATED and DISSOCIATED ACID. Since only a few of the acid particles release H+ ions, the position of EQUILIBRIUM lies well to the LEFT.

Answer 7

Concentrated in chemistry refers to the amount (number of moles) in a particular volume of liquid; a concentrated acid means there are a lot of acid molecules crammed into a small volume of liquid.

Answer 8

Dilute acids can be considered to be watered down versions of the real stuff-i.e. lots of water and hardly any acid.

Answer 9

Reactions of acids involve the H+ ions reacting with other substances. If the concentration of H+ ions is HIGHER, the RATE OF REACTION will be faster, so STRONG ACIDS will be MORE REACTIVE than WEAK ACIDS of the same concentration.

Answer 10

The pH of an acid or alkali is a measure of the CONCENTRATION of H+ ions in the solution.

Answer 11

Remember acid strength (i.e. strong or weak) tells you what PROPORTION of the acid molecules IONISE in water. The lower the pH, the higher the concentration of H+ ions and so the more acidic the solution is. The pH of a strong acid will be lower than a weak acid if both acids are at the same concentration. This is because strong acids dissociate more than weak acids resulting in a larger concentration of H+ ions.

Answer 12

You can calculate the change in H+ ion concentration with the equation: Factor H+ ion concentration changes by = 10-x (N.b this is 10 to the power - x. x is the difference in pH. So if pH falls from 7 to 4 the difference is -3, and the factor the H+ ion concentration has increased by is 10-(-3)= 10 to the power 3). As the pH decreases by one unit, the hydrogen ion concentration of the solution increases by a factor of 10. When the concentration of hydrogen ions is expressed using powers of 10, the pH is equal to the negative of the power number. Example: In a solution of pH 2, what is the concentration of H+(aq)? pH of solution = 2 [H+(aq)] = 10-2 mol l-1

Answer 13

- Acids don't produce hydrogen ions until they meet water. So, for example hydrogen chloride gas isn't acidic. - An H+ ion is just a proton.

Answer 14

1) Acid STRENGTH (i.e. strong or weak) tells you WHAT PROPORTION of the acid molecules IONISE in water. 2) The CONCENTRATION of an acid is different. Concentration measures HOW MUCH ACID there is in a certain volume of water. Concentration is basically how WATERED DOWN your acid is. 3) The larger the amount of acid there is in a certain volume of liquid, the MORE CONCENTRATED the acid is. 4) So you have a DILUTE (not very concentrated) but STRONG acid, or a CONCENTRATED BUT WEAK acid. 5) pH will DECREASE with INCREASING acid concentration REGARDLESS of whether it's a strong or weak acid.

Answer 15

A salt is an ionic compound made from any metal and any non-metal.

Answer 16

Soluble salts dissolve in water and can be made by reacting an appropriate acid with either: 1) An ALKALI (metal hydroxide-soluble in water e.g. NaOH). 2) A BASE (insoluble metal hydroxide or metal oxide-not soluble in water e.g. MGO). 3) A METAL CARBONATE e.g. CaCO3. 4) A suitably reactive metal e.g. Na or Zn.

Answer 17

Substances that can react with acids and neutralise them to make a salt and water are called bases. All metal oxides and hydroxides are bases. These soluble compounds are ALKALIS. For example, copper oxide and sodium hydroxide are bases. Soluble metal hydroxides are alkalis because they dissolve in water to form OH- ions. The products of these neutralisations are a salt and water.

Answer 18

acid + base = salt + water These are neutralisation reactions. The H+ ions of the acid react with the 02- of the alkali.

Answer 19

The name of the salt produced depends on the metal ion in the oxide or hydroxide and the acid that is used. The first part of the name of the salt is the metal ion in the ion/hydroxide and the second part of the name comes from the acid that is used.

Answer 20

acid + alkali ͢ salt + water

Answer 21

These are all neutralisation reactions. The H+ ions of the acid reacts with the OH- of the alkali.

Answer 22

acid + metal carbonate ͢ salt + water + carbon dioxide

Answer 23

Soluble salts can be made from ACIDS by reacting them with SOLID INSOLUBLE SUBSTANCES, such as metals, metal oxides, hydroxides or carbonates. The solid is added to the acid until no more reacts and the excess solid is filtered off to produce a solution of the salt. Salt solutions can be crystallised to produce solid salts.

Answer 24

If you are making a soluble salt by adding an insoluble reagent to an acid, you can add it in excess and separate it out at the end of the reaction using filter paper. Many metal oxides handsome metal carbonates are insoluble, so this is the method you'd use if you're using any of those. E.g. if you want to make copper chloride, you could mix hydrochloric acid and copper oxide. 1. Gently WARM the dilute acid using a BUNSEN BURNER, then turn off the Bunsen burner. 2. Add the INSOLUBLE REACTANT/BASE to the ACID a bit at whilst stirring it- it will form a soluble product in the acid as it reacts. 3. Keep adding the insoluble reactant until it is in excess. (until no more reacts). You'll know when this is because even after stirring, the excess solid won't react, it will just SINK to the bottom of the flask. This shows that all the acid has been neutralised and the reaction has finished. 4. Then FILTER out the EXCESS solid to get the salt solution. This is done using FILTER PAPER and a FUNNEL. 5. You'll be left with a salt solution at the end of the filtration. You can convert this into pure, solid crystals of salt using crystallisation. To do this you first need to heat the solution using a WATER BATH or an ELECTRIC HEATER to evaporate some of the water and make the solution more concentrated. Then, stop heating it and leave the solution to cool. CRYSTALS of the salt should form, which can be FILTERED out of the solution and then dried..

Answer 25

When metals react with other substances the metal atoms loses an electron to the nn-metal to form a full outer shell and to form positive ions. The reactivity of a metal is related to its tendency to form POSITIVE IONS.. A positive ion can also be called a CATION. So a metal that is more able to lose electrons to become a positive ion is much more reactive than a metal that is happy to hold onto its electrons.

Answer 26

You can see how reactive metals are by monitoring the rate of hydrogen production when they react with an acid. The more reactive the metal, the faster the reaction will go.

Answer 27

The speed of the reaction is indicated by the rate at which bubbles of hydrogen are given off- a speedy reaction is shown by bubbles being produced rapidly.

Answer 28

- Very reactive metals like Potassium, Lithium, and Calcium react EXPLOSIVELY. - Less reactive metals such as Magnesium, Zinc and Iron react LESS VIOLENTLY. - Copper won't react with cold, dilute acids.

Answer 29

The production of hydrogen can be detected using the burning splint test. This involves putting a lit splint at the mouth of the tube containing the metal and the acid. If hydrogen is there, you'll hear a 'squeaky pop'. The more reactive a metal, the ore hydrogen is produced in a certain amount of time and the louder the 'squeaky pop'.

Answer 30

Metals can be arranged in order of their reactivity in a reactivity series. The metals potassium, sodium, lithium, calcium, magnesium, zinc, iron and copper can be put in order of their reactivity from their reactions with water and dilute acids.

Answer 31

The REACTIVITY SERIES is a list of metals that are arranged in order of how reactive they are. The most reactive metals are at the top and the least reactive metals are at the bottom. 1. Potassium K 2. Sodium Na 3. Lithium Li 4. Calcium Ca 5. Magnesium Mg 6. CARBON C 7. Zinc Zn 8. Iron Fe 9. Copper Cu

Answer 32

Even though CARBON and HYDROGEN are non-metals, they are often included in the series so you can compare where metals are in relation to them.

Answer 33

It was found by comparing the relative reactivity of different metals with either an ACID or WATER, and then putting them in order from the most reactive to the least reactive, the order you get is the reactivity series. The higher a metal is in the reactivity series, the more easily it reacted with the water or acid.

Answer 34

You can investigate the reactivity of metals by measuring the TEMPERATURE CHANGE of the reaction with an acid or water over a set time period. If you use the same mass and surface area of metal each time, then the more reactive the metal, the greater the temperature change should be.

Answer 35

By knowing the order of reactivity than cientists could begin to predict exactly what new substances would be formed and use this knowledge to develop a wide range of different materials and processes. *A more reactive metal can displace a less reactive metal from a compound.

Answer 36

-Dilute acids react with some metals to produce salt and hydrogen. Metal + Acid ͢ Salt + Hydrogen This reaction can be remembered as MASH. Metals more reactive than HYDROGEN react with dilute acids.

Answer 37

The first part of name comes from the METAL and the second part comes from the ACID that is used. The way to remember which acid produces which salt is in the name. HydroCHLORIC acid produces CHLORIDE salts and SULFURIC acid produces SULFATE salts.

Answer 38

- Potassium and Sodium react EXPLOSIVELY. - Calcium reacts VIOLENTLY to give hydrogen gas. - Magnesium reacts RAPIDLY to give hydrogen gas. - Zinc reacts MODERATELY FAST to give hydrogen gas. - Iron reacts SLOWLY to give hydrogen gas. - Copper NO reaction occurs.

Answer 39

Most metals do not react with cold water. However, those above magnesium will react, to form a metal hydroxide (an alkaline) and hydrogen gas: Metal + Wate ͢ Metal hydroxide + Hydrogen

Answer 40

- Potassium reacts VERY VIOLENTLY. The HYDROGEN gas burns with a LILAC FLAME. - Sodium reacts reacts VIOLENTLY. The HYDROGEN gas burns with a YELLOW FLAME - Calcium reacts STEADILY. - Magnesium reacts VERY SLOWLY. - Zinc, Iron and Copper do NOT react.

Answer 41

Metals react with oxygen to produce metal oxides. Metal + Oxygen ͢ metal oxide

Answer 42

The reaction are oxidation reactions because the metals gain oxygen.

Answer 43

Oxidation can be defined as the gain of oxygen by an element or compound.

Answer 44

Reduction can be defined as the loss of oxygen from a compound.

Answer 45

Displacement reactions involve one METAL REPLACING another one out of a COMPOUND. A more reactive metal will displace a less reactive metal from its compound.

Answer 46

Unreactive metals such as gold are found in the Earth as the metal itself.

Answer 47

Most metals are found as COMPOUNDS that require chemical reactions to extract the metal.

Answer 48

The rest of the metals we get by extracting them from METAL ORES, which are mined from the ground.Most metals require chemical reactions to extract the metal.

Answer 49

A reaction that separates a metal from its oxide is called REDUCTION. *Reduction involves the loss of oxygen from an element or compound.

Answer 50

A metal below carbon can be extracted from it ore by reducing it in a reaction with carbon. In this reaction, the ore is reduced as oxygen is removed from it and carbon gains oxygen so it is oxidised.

Answer 51

Metals BELOW CARBON in the reactivity series can be extracted by REDUCTION using CARBON. This is because carbon can only take the oxygen away from metals which are less reactive than carbon itself.

Answer 52

Metals higher than carbon in the reactivity series, or that react in different ways with carbon, have to be extracted using ELECTROLYSIS, which is expensive.

Answer 53

- Oxidation is the LOSS of electrons. | - Reduction is the GAIN of electrons.

Answer 54

To remember the electron definition of oxidation and reduction we use OILRIG. O oxidation I is L loss R reduction I is G gain -REDuction and Oxidation happens at the SAME TIME- hence the term REDOX.

Answer 55

During a displacement reaction oxidation and reduction occurs.

Answer 56

- Fe has been oxidised as it has gained oxygen and lost electrons. - Cu has been reduced because it has gained electrons to become stable and have a full outer shell. It has also lost oxygen.

Answer 57

-Ionic equations for displacement reactions only concentrate on the substances which are oxidised or reduced, so you don't Oxidation half equation (loss of electrons): Fe ͢ Fe2+ + 2e- Reduction half equation (gain of electrons): Cu2+ + 2e- ͢ Cu Overall ionic equation: Fe + Cu2+ ͢ Fe2+ + Cu Remember- if anything is repeated (e.g. in this case 2e-) cross it out!!!

Answer 58

When an ionic compound is melted or dissolved in water, the ions are free to move about within the liquid or solution. These liquids and solutions are able to conduct electricity and are called electrolytes.

Answer 59

Electrolysis is the process by which ionic (metal and non-metal) substances are decomposed (broken down) into simpler substances when an electric current is passed through them.

Answer 60

1) During electrolysis, an electric current is passed through an electrolyte (a MOLTEN or DISSOLVED ionic compound). The ions move towards the electrodes, where they react, and the compound DECOMPOSES. 2) The POSITIVE IONS in the electrolyte will move towards the cathode (negatively charged electrode) and GAIN electrons (they are REDUCED). 3) The NEGATIVE IONS in the electrolyte will move towards the ANODE (positively charged electrode) and LOSE electrons (they are OXIDISED). 4) This creates a FLOW OF CHARGE through the ELECTROLYTE as ions travel to the electrodes. 5) As ions gain or lose electrons, they form the uncharged element (they become atoms or molecules) and are RELEASED from the electrolyte. These atoms or molecules are the products of electrolysis.

Answer 61

-Electrolysis requires a liquid to conduct electricity, called the ELECTROLYTE . -An IONIC SOLID CAN'T be electrolysed because the ions are in fixed positions and can't move to carry current. Whereas... -Electrolytes contain free ions-they're usually a molten or dissolved ionic substance. The ions can MOVE FREELY and conduct electricity. It's the FREE IONS which conducts the electricity and allow the whole process to work.

Answer 62

Electrolysis always involves an OXIDATION and a REDUCTION reaction.

Answer 63

- Reduction is happening at the negative electrode as the positive ions are gaining electrons. - Oxidation is happening at the positive electrode as the negative ions are losing electrons.

Answer 64

Molten ionic liquids, e.g. lead bromide, are always broken up into their ELEMENTS. - Positive METAL ions are REDUCED to the element at the CATHODE, e.g. Pb2+ + 2e- ͢ Pb - Negative NON-METAL ions are OXIDISED to the element at the ANODE, e.g. 2Br- ͢ Br2 + 2e-

Answer 65

An electrolyte is just a liquid or solution that can conduct electricity.

Answer 66

An electrode is a solid that conducts electricity and is submerged in a electrolyte.

Answer 67

Electrons should be made out of an inert material, such as graphite or platinum, so they don't react.

Answer 68

Binary compounds are ionic compounds containing two elements which are ions- a positive metal ion and a negative non-metal ion.

Answer 69

Electrolysis of the molten binary compounds gives the neutral metal and non-metal elements. During the electrolysis of these substances, the metal ions move to the cathode and gain electrons to become neutral, while the non-metal ions move to the anode and lose electrons to become neutral.

Answer 70

When a simple ionic compound (eg lead bromide) is electrolysed in the molten state using inert electrodes, the metal (lead) is produced at the cathode and the non-metal (bromine) is produced at the anode.

Answer 71

Metals can be extracted from molten compounds using electrolysis.

Answer 72

Electrolysis is used if the metal is too reactive to be extracted by reduction with carbon or if the metal reacts with carbon.

Answer 73

Large amounts of energy are used in the extraction process to melt the compounds and to produce the electrical current.

Answer 74

*Aluminium is manufactured/extracted by the electrolysis of a MOLTEN MIXTURE of aluminium OXIDE (called bauxite ore) and CRYOLITE using CARBON as the positive electrode (ANODE).

Answer 75

Aluminium oxide has a VERY HIGH melting temperature so it's mixed with CRYOLITE to lower the melting point.

Answer 76

1. The main ore of aluminium is BAUXITE, which can be mined and purified to give ALUMINIUM OXIDE. Aluminium is then extracted by ELECTROLYSIS. 2. Aluminium has a VERY HIGH melting temperature of 2070℃ so melting it would be very EXPENSIVE. Instead, the aluminium oxide is DISSOLVED in molten cryolite (a less common ore of aluminium). This brings the melting point DOWN to about 900℃, which SAVES ENERGY, making the process CHEAPER and EASIER. 3. The electrodes are made of CARBON (graphite), a good conductor of electricity. And the MOLTEN MIXTURE contains FREE IONS-so it'll CONDUCT ELECTRICITY. 4. The POSITIVE Al3+ IONS are attracted to the NEGATIVE ELECTRODE where they EACH PICK UP THREE ELECTRONS and turn into neutral ALUMINIUM ATOMS. These then SINK to the bottom of the electrolysis tank. 5. The NEGATIVE O2- IONS are attracted to the POSITIVE ELECTRODE where they EACH LOSE TWO ELECTRONS. The neutral oxygen atoms will then combine to form O2 molecules. 6. Because of the heat, the oxygen produced at the anode reacts with the graphite (carbon) anode causing it to react (corrode) and produce carbon dioxide: C (s) + O2 (g) ͢ CO2 (g)

Answer 77

Because of the heat, the oxygen produced at the anode reacts with the graphite (carbon) anode causing it to react (corrode) and produce carbon dioxide: C (s) + O2 (g) ͢ CO2 (g) Therefore, the graphite anodes need replacing on a frequent basis.

Answer 78

The half equation for the reaction taking place at the electrodes when aluminium oxide is electrolysed are: Negative electrode: Al3+ + 3e- ͢ Al Positive electrode: 2O2- ͢ O2 + 4e-

Answer 79

Sometimes there are more than two types of free ions in the electrolyte. For example, if a salt is dissolved in water there will be some H+ and OH- ions as well as the ions from the salt in the solution. In this situation, the products of electrolysis depend on how REACTIVE the ELEMENTS involved are.

Answer 80

(Remember-in AQUEOUS SOLUTIONS, as well as the IONS from the ionic compound there will be HYDROGEN IONS from the ionic compound, there will be HYDROGEN IONS H+ and HYDROXIDE IONS OH- from the water.) At the cathode, if H+ INS AND METAL IONS are present, HYDROGEN GAS will be produced if the metal is MORE REACTIVE than hydrogen (e.g. sodium ions). If the metal ions are from an element LESS REACTIVE than hydrogen (e.g. copper ions), a solid layer of the PURE METAL will be produced instead.

Answer 81

This is because IT IS HIGH IN THE REACTIVITY SERIES, and, as covered previously, the most REACTIVE METALS ARE THE ONES BEST ABLE TO RID THEMSELVES OF ELECTRONS. As a result H+ ions present in small amounts in the water are forced to accept electrons at the cathode.

Answer 82

If OH- and HALIDE IONS (F-, Cl-, Br-, etc) are present, the corresponding HALOGEN (F2, Cl2, Br2, etc) is produced. But, if NITRATE, NO3-, or SULPHATE, are present, OYGEN gas is produced instead. If NO halide is present, then OH- ions are discharged and OXYGEN and WATER will be formed.