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Chemistry > C4.2 - identifying the products of chemical reactions > Flashcards

C4.2 - identifying the products of chemical reactions Flashcards

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1
Q

How do you detect carbon dioxide gas?

A

You test for carbon dioxide by using limewater.

Limewater is a calcium hydroxide solution

It turns cloudy when carbon dioxide is bubbled through it

This change is caused by the calcium hydroxide reacting with the carbon dioxide to form water and a white precipitate of calcium carbonate.

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2
Q

What is the balanced equation for the reaction between calcium hydroxide (limewater) and carbon dioxide ?

A

Ca(OH)2 (aq) + CO2(g) → CaCO3(s) + H2O (l)

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3
Q

What is limewater .

A

It is a calcium hydroxide solution

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4
Q

Is blue litmus paper used to test for acids or alkalis ?

A

Acids

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5
Q

Is red litmus usually used to test for acids or alkalis

A

Alkalis

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6
Q

How do you detect chlorine gas?

A
  1. Use a drop of water to dampen a piece of blue litmus paper
  2. Hold the paper near to a container that holds the substance
  3. If chlorine is present the litmus paper turns red then white
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7
Q

Why does damp blue litmus paper turn red and then white when chlorine is present?

A

Chlorine gas reacts with water to produce an acidic solution which is also an effective bleach.

The acidic solution formed on the damp blue litmus paper turns it red

The bleach then causes the colour to change from red to white

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8
Q

How do you carefully smell substances in the lab?

A
  1. With the container away from your nose breath in enough ear to almost fill your lungs.
  2. Hold the container a few cm away from your nose and waft the smell towards you. Take a cautious sniff.

(Holding the container away from your nose makes sure you don’t breath in a lot of the substance. )

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9
Q

Why do you hold the container away from your nose when smelling a substance?

A

Holding the container away from your nose makes sure you don’t breath in a lot of the substance.

This also ensures that should any of these substances escape, it will not go up your nose

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10
Q

How do you detect hydrogen gas?

A
  • place a lighted splint near the mouth of the container of gas
  • if hydrogen is present, it should ignite with a squeaky pop
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11
Q

How do you detect oxygen gas?

A

Place a glowing splint near the mouth of the container of gas

If oxygen is present the splint should relight

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12
Q

Write a word equation for the catalytic decomposition of hydrogen peroxide, H2O2.

A

Water + oxygen —> hydrogen peroxide

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13
Q

Write a balanced symbol equation for the catalytic decomposition of hydrogen peroxide, H2O2.

A

2H2O —> O2 + 2H2O

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14
Q

Write a word equation and a balanced symbol equation for the combustion of hydrogen.

A

Hydrogen + oxygen —> water

2H2 + O2 —> 2H2O

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15
Q

Explain why hydrogen pops with a lighted splint.

A

Hydrogen is highly flammable so when hydrogen reacts with oxygen in the air it creates a small explosion which results in the pop sound.

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16
Q

Write a word equation for the reaction between zinc and hydrochloric acid.

A

Zinc + hydrochloric acid —> zinc chloride + hydrogen

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17
Q

Write a balanced symbol equation for the reaction between zinc and hydrochloric acid.

A

Zn+ 2HCl —> ZnCl2 + H2

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18
Q

Write a word equation and a balanced symbol equation for the reaction between calcium carbonate and hydrochloric acid.

A

Calcium carbonate + hydrochloric acid —> calcium chloride + water + carbon dioxide

CaCO3 (s) + 2HCl(aq) —> CaCl2 (aq) + H2O (l) + CO2 (g)

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19
Q

What is a flame test?

A

It is a test that helps to identify metal ions in compounds from the colour that they produce in a flame

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20
Q

What happens when metal ions are heated in terms of energy transfer

A

When metal ions are heated energy is transferred to their electrons.
This makes their electrons move into higher electron shells.

When they move back to their normal electron shells, energy is transferred to the surroundings as radiation, which you see as light.

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21
Q

What is the flame test colour for lithium?

A

Red

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22
Q

What is the flame test colour for sodium

A

Yellow

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23
Q

What is the flame test colour for potassium

A

Lilac

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24
Q

What is the flame test colour for calcium

A

Orange red

25
Q

What is the flame test colour for copper

A

Green-blue

26
Q

What are the steps for doing a flame test?

A
  1. Dip the clean loop into the test powder or solution
  2. Use the handle to hold the loop in the edge of a roaring blue flame
  3. Record the flame colour
27
Q

Why do you clean the wire loop between each flame test?

A

It ensures it is not contaminated with pervious substances so you will not confuse flame colours or mix the substances

28
Q

How do you clean a wire loop?

A

By dipping it several times in hydrochloric acid and then rinsing it with distilled water

If you hold it in a Bunsen burner flame there will be no change in the colour of the flame

29
Q

What group are soluble in water

A

Group 1 metal hydroxides

30
Q

What is the balanced equation for the reaction between copper (II) sulfate and sodium hydroxide

A

CuSO4 (aq) + 2NaOh (aq) —> Cu(OH)2 (S) —> Na2SO4 (aq)

31
Q

What colour hydroxide precipitate is does iron (II) form

A

Green

32
Q

What colour hydroxide precipitate does iron (III) form

A

Orange brown

33
Q

What colour hydroxide precipitate does copper (II) form

A

Blue

34
Q

What colour hydroxide precipitate does calcium form?

A

White

35
Q

What colour hydroxide precipitate does zinc form

A

White

36
Q

How can you tell if the ion present is calcium is zinc from a precipitate test?

A

If you add an excess sodium hydroxide solution zinc hydroxide dissolves to form a colourless solution but calcium hydroxide does not dissolve

37
Q

What happens during a sulfate test?

A

Barium ions react with sulfate ions to produce white, insoluble barium sulfate

38
Q

What is the ionic equation for a sulfate test?

A

Ba2+ (aq) + SO42- (aq) —> BaSO4 (s)

39
Q

What is the method for a sulfate test?

A
  1. Add a few drops of dilute hydrochloric acid
  2. Then add a few drops of barium chloride solution BaCl2 (aq)
  3. If sulfate ions are present you will get a white precipitate
40
Q

How do you detect carbonate ions?

A

Hydrogen ions from dilute acids react with carbonate ions to produce carbon dioxide and water

41
Q

What is the ionic equation for a carbonate test?

A

2H+ (aq) + CO32- (aq) —> CO2 (g) + H2O(l) a

42
Q

What is the method for a carbonate test

A
  1. Add a few drops of dilute hydrochloric acid
  2. If carbonate ions are present bubbles of gas will be produced. You can confirm this is carbon dioxide by bubbling it through limewater
43
Q

How do you detect halide ions? (Include method)

A

Silver fluoride is soluble in water but the other silver halides are insoluble.

  1. Add a few drops of dilute nitric acid
  2. Add a few drops of silver nitrate solution (AgNO3)
  3. Observe colour of precipitate formed
    If one of these ions is present you get a precipitate
44
Q

What is the colour of the silver halide precipitate formed by chloride

A

White

45
Q

What is the colour of the silver halide precipitate formed by bromide?

A

Cream

46
Q

What is the colour of the silver halide precipitate formed by iodide?

A

Yellow

47
Q

What is an instrumental method of analysis?

A

A technique for analysing a substance that depends upon a machine

48
Q

What are the advantages of an instrumental method of analysis?

A

Sensitivity

Accuracy

Speed

49
Q

Why is sensitivity advantageous?

A

This means it can analyse small amounts of substances.

This is useful if the substance is expensive or difficult to obtain

50
Q

What is accuracy advantageous?

A

the instruments are very accurate.

This means they can be calibrated using internationally accepted standards

51
Q

Why is speed advantageous

A

Because the instruments can carry out analyses quickly and they can run all the time

52
Q

What is a gas chromatogram?

A

A gas chromatogram is a chart that represents the different substances in a mixture,

53
Q

How do you interpret gas chromatograms?

A

Each peak represents a substance present in the mixture

The areas under each peak show the relative amounts of each substance in the mixture

The retention time is different for different substances

54
Q

What is the retention time?

A

It is the time taken for a substance to travel through the chromatography column

55
Q

What is a mass spectrometer?

A

A machine that can measure masses of atoms and molecules

56
Q

What is a mass spectrometer used for?

A

To analyse the relative amounts of isotopes of an element and the structure of molecules

57
Q

How does a mass spectrometer analyse molecules?

A

The sample molecules are ionised by the machine to form molecular ions.

These may break up to form fragments, which the machine can separate and detect

58
Q

How do you interpret mass spectra?

A

In a mass spectrum:

Each peak represents a fragment of the molecule

The peak on the far right represents the molecular ion

The mass to charge ratio of the molecular ion peak is equal to the Mr of the molecule

Chemistry (15 decks)

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