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GCSE > Chemistry 3b > Flashcards

Chemistry 3b Flashcards

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1
Q

What is a mole?

A

The name given to a certain number

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2
Q

How can the concentration of a solution be measured?

A

In moled per dm3 (i.e. moles per litre)

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3
Q

What is the statement about concentration?

A

The more solute you dissolve in a given volume, the more crowded the solute molecules are and the more concentrated the solution

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4
Q

What are titrations used to find out?

A

Concentrations and exactly how much acid is needed to neutralise a quantity of alkali (or the other way around)

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5
Q

What is the first step of titration?

A

Put alkali in a flask along with some indicator, either phenolphthalein or methyl orange

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6
Q

Why don’t you use universal indicator?

A

Because it changes colour gradually and you want a definite colour change

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7
Q

What is the second step of titration?

A

Add the acid, a bit at a time, to the alkali using a burette giving the flask a regular swirl, go slowly when you think its almost neutralised (one drop at a time)

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8
Q

What is the third step of titration?

A

The indicator changes colour when all the alkali has been neutralised-phenolphtalein is pink in alkalis but colourless in acids, methyl orange is yellow in alkalis but red in acids

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9
Q

What is the fourth step of titration?

A

Record the amount of acid used to neutralise the alkali, its best to repeat this process a few times, making sure you get roughly the same result each time. You can then work out the mean of your results

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10
Q

What is the triangle for titration calculations?

A

N (number of moles) on top, then c x v on the bottom (concentration times volume)

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11
Q

What does concentration =?

A

Moles ÷ volume

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12
Q

How do you work out the concentration of an acid in moles per dm3?

A

Work out how many moles of the known substance you have by multiplying the concentration and volume. Then write down the balanced equation of the re`action and work out how many moles of the unknown stuff you must have had. Lastly work out the concentration of the unknown stuff

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13
Q

How do you work out the concentration in grams per dm3?

A

Work out the relative formula mass for the acid and then convert the concentration in moles into grams

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14
Q

What is the triangles for titration calculations in grams?

A

M (mass in grams) on top and then n x m underneath (number of moles x relative formula mass)

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15
Q

How can you measure the amount of energy released by a chemical reaction?

A

By taking the temperature of the reagents, mixing them in a polystyrene cup and measuring the temperature of the solution at the end of the reaction

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16
Q

What is the biggest problem with energy measurements?

A

The amount of energy lost to the surroundings

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17
Q

How can you reduce the amount of energy lost to the surroundings?

A

By putting the polystyrene cup into a beaker of cotton wool to give more insulation and by putting a lid on the cup to rescue energy lost by evaporation

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18
Q

What sort of method does this reaction work for?

A

Reactions of solids with water e.g. dissolving ammonium nitrate in water, as well as for neutralisation reactions

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19
Q

What is an example of an experiment?

A

Place 25 cm 3 of dilute hydrochloric acid in polystyrene cup and record its temperature. Put 25 cm3 of dilute sodium hydroxide in a measuring cylinder and record its temperature. As long as they’re at the same temperature, add the alkali to the acid and stir. Take the temperature of the mixture every 30 seconds and record the highest temperature it reaches

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20
Q

What is an exothermic reaction?

A

One which gives out energy to the surroundings, usually in the form of hear and usually shown by a rise in temperature e.g. fuels burning or neutralisation reactions

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21
Q

What is an endothermic reaction?

A

One which takes in energy from the surroundings, usually in the form of heat and usually shown by a fall in temperature e.g. photosynthesis

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22
Q

What happens to bonds during a chemical reaction?

A

Old bonds are broken and new bonds are formed. Energy must be supplied to break existing bonds-endothermic process. Energy is released when new bonds are formed-exothermic process

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23
Q

What happens during an endothermic reaction?

A

The energy required to break old bonds is greater than the energy released when new bonds are formed

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24
Q

What happens during an exothermic reaction?

A

The energy released in bond formation is greater than the energy used in breaking old bonds

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25
Q

How is fuel energy calculated?

A

Using calorimetry. You can burn the fuel and use the flame to heat up some water, calorimetry uses a glass or metal container usually made of copper as it conducts heat well

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26
Q

What is the method of calorimetry?

A

Put 50g of water in the copper can and record its temperature. Weigh the spirit burner and life. Put the spirit burner underneath the can and light the wick. Heat the water, stirring constantly until the temperature reaches about 50ºC. Put out the flame using the burner lid, and measure the final temperature of the water. Weigh the spirit burner and lid again

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27
Q

How to work out the energy per gram of methylated spirit (meths)?

A

Mass of burner+lid before heating=68.75g. Mass of burner+lid after heating=67.85g. Mass of meths burnt=0.9g. Then temperature of water in copper can before heating=21.5ºC, then after heating=52.5ºC, temperature change in 50g of water due to heating=31ºC. So 0.9 g of fuel releases enough energy to heat up 50g of water by 31ºC. It takes 4.2 joules of energy to heat up 1g go water by 1ºC (specific heat capacity of water). Energy released in experiment =50 x 4.2 x 31=6510 joules. So 0.9g of meths releases 6510 joules of energy meaning 1g of meths releases 6510/0.9=7233j or 7.233 kj

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28
Q

Why would the answer often be much lower than the actual energy content?

A

Energys wasted heating the can, air etc

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29
Q

What is the formula to work out the energy per gram of methylated spirits?

A

Energy transferred=mass of water x specific heat capacity of water x temperature change

30
Q

What are the consequences of fuels providing energy?

A

We use the fuel e.g. to generate electricity and to power cars, but it has various effects on the environment. Burning fossil fuels releases CO2 causing global warming and other types of climate change. It’ll be expensive to slow this down and put it right and developing alternative energy sources costs money. Crude oil is running out we use a lot of fuels made from crude oil e.g. petrol and diesel, and as it runs out it will get more expensive. Meaning everything thats transported by lorry, train or plane gets more expensive too, so the price of crude oil has a big economic effect

31
Q

What do energy level diagrams show?

A

Whether is exo or endothermic

32
Q

What are graphs of endothermic reactions like?

A

Energy change is negative. The products are at a lower energy than the reactants. The difference in height represents the energy given out in the reaction (per mole). The initial rise in the line represents the energy needs to break the old bonds this is the activation energy

33
Q

What are the graphs of exothermic reactions like?

A

Energy change is positive. The products are at a higher energy than the reactants so energy change is positive . The difference in height represents the energy energy taken in during the reaction (per mole)

34
Q

What is activation energy lowered by?

A

Catalysts

35
Q

What does the activation energy represent?

A

The minimum energy needed by renting particles to break their bonds

36
Q

What does a catalyst provide?

A

A different pathway for a reaction that has a lower activation energy so the reaction happens more easily and more quickly. This is represented by the lower curve on the diagram showing a lower activation energy. The overall energy change for the reaction, energy change remains the same though

37
Q

How do you work out bond energy, example-the formation of HCL?

A

Breaking one mole H-H and one mole of Cl-Cl bonds requires 436+242=678 kj. Forming two moles of H-Cl bonds releases 2 x 431=862kj. Overall more energy is released than is used to form the products: 862-678=184kj/mol released. Since this is energy released, if we wanted to show energy change, we’d need to put a negative sign in front of it to indicate that its an exothermic reaction (energy change=-184kj/mol

38
Q

What do hydrogen and oxygen react to produce?

A

Water, which isn’t a pollutant

39
Q

What sort of reaction is the reaction between hydrogen and oxygen?

A

Exothermic, it releases energy. You can get energy by reacting hydrogen and oxygen either in a combustion engine or in a fuel cell

40
Q

What can be hydrogen gas used for?

A

It can be burnt in oxygen as a fuel in the combustion engines of vehicles

41
Q

What are pros of this?

A

Hydrogen combines with oxygen in the air to form just water so its very clean

42
Q

What are the cons of this?

A

You need a special expensive engine. Although hydrogen can be made from water, which theres plenty of, you still need to use energy from another source to make it. Also hydrogens hard to store safely as its very explosive

43
Q

What is a fuel cell?

A

A fuel cell is an electrical cell thats supplied with a fuel and oxygen and uses energy from the reaction between them to generate electricity. Hydrogen can be used n a hydrogen-oxygen fuel cell

44
Q

When were fuel cells developed?

A

In the 1960s as part of the space programme, to provide electrical power on spacecraft-they were more practical than solar cells and safer than nuclear power

45
Q

What is the good thing about fuel cells?

A

Unlike batteries, a fuel cell doesn’t run down or need recharging from the mains, it’ll produce energy in the form of electricity and heat as long as fuel is supplied

46
Q

What is the car industry developing?

A

Fuel cells to replace conventional petrol/diesel engines

47
Q

Why would fuel cells be useful for cars?

A

They don’t produce any conventional pollutants, no greenhouse gases, no nitrogen oxides, no sulfur dioxide, no carbon monoxide. The only by products are water and heat which would be a major advantage in cities where air pollution from traffic is a big problem.

48
Q

How else would fuel cells be useful?

A

They could eventually help countries to become less dependent on crude oil

49
Q

Why are they not likely to mean the end of either conventional power stations or our dependence on fossil fuels?

A

Hydrogen is a gas so it takes up loads more space to store than liquid fuels like petrol. Its very explosive so its difficult to store safely. Also hydrogen fuel is often made either from hydrocarbons from fossil fuels or by electrolysis of water which uses electricity which has to be generated usually by burning fossil fuels

50
Q

What do metals always form?

A

Positive ions

51
Q

How can you test for various metal ions?

A

By putting your substance in a false and seeing what cooly the flame goes

52
Q

What colour flame is lithium Li+?

A

(L-ithium L-ipstick, red) crimson

53
Q

What colour flame is sodium Na+?

A

(S-odium S-treetlight yellow) Yellow

54
Q

What colour flame is Potassium K+?

A

(P-otassium P-urple) Lilac

55
Q

What colour flame is calcium Ca2+?

A

(C-alcium Bri-CK red) red

56
Q

What colour flame is barium Ba2+?

A

Green

57
Q

How do you flame test a compound in the lab?

A

Dip a clean wire loop into a sample of the compound, and put the wire loop in the clear blue part of then bunsen flame as thats the hottest bit. First make sure the wire loop is really clean by dipping it into HCL and rinsing it with distilled water

58
Q

What is another way to get for metal ions?

A

Many metal hydroxides are insoluble and precipitate out of solution when formed, some have a characteristic colour. So you add a few drops of sodium hydroxide to a solution of your compound, if you get a coloured insoluble hydroxide (precipitate) you can tell which metal was in the compound

59
Q

What colour is the precipitate for calcium Ca2+?

A

(Calcium is good for teeth and bones which are white) White

60
Q

What colour is the precipitate for Copper (II) Cu2+?

A

(Cop=police=blue uniform) Blue

61
Q

What colour is the precipitate for Iron (II), Fe2+?

A

(Iron 2, but not its) Green

62
Q

What colour is the precipitate for Iron (III) Fe3+?

A

(Iron 3, but not its) Brown

63
Q

What colour is the precipitate for aluminium Al3+?

A

White then redissolves in excess NaOH to form a colourless solution

64
Q

What colour is the precipitate for magnesium MG2+?

A

White

65
Q

What are two examples of ionic reactions to show the pattern?

A

Ca2+(aq) + 2OH-(aq)=Ca(OH)2(s) and Fe3+(aq)+3OH-(aq)=Fe(OH)3(s)

66
Q

How do you test for negative ions, carbohydrates?

A

Test for carbon dioxide by bubbling it through limewater, it its carbon dioxide the limewater goes cloudy. You can use this to test for carbonate ions (CO3 2-) since carbonates react with dilute acids to form carbon dioxide

67
Q

What is the formula for this?

A

Acid+Carbonate=salt+water+carbon dioxide

68
Q

How do you test for halide ions (chloride, bromide or iodide)?

A

Add dilute nitric acid followed by silver nitrate

69
Q

What happens to chloride?

A

It give a white precipitate of silver chloride (Ag+(aq)+Cl-(aq)=AgCl(s))

70
Q

What happens to bromide?

A

It gives a cream precipitate of silver bromide (Ag+(aq)+Br-(aq)=AgBr(s))

71
Q

What happens to iodide?

A

It gives a yellow precipitate of silver bromide (Ag+(aq)+I-(aq)=AgI(s))

72
Q

How do you test for sulphate ions?

A

Add dilute HCL followed by barium chloride solution. A white precipitate of barium sulphate means the original compound was a sulphate (Ba2+(aq)+SO4 2-(aq)=BaSO4(s))

GCSE (26 decks)

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