3 Elements and compounds

Question 1

Define an element

Answer 1

A substance containing only one type of atom

Question 2

Define a compound

Answer 2

A substance containing two or more different types of atoms chemically bonded together

Question 3

Write the chemical equation for the decomposition of H₂O₂

Answer 3

2H₂O₂ –> 2H₂O + O₂

Question 4

What is a molecule?

Answer 4

When two or more atoms are chemically bonded together

Question 5

What is the word equation for the decomposition of hydrogen peroxide

Answer 5

hydrogen peroxide –> water + oxygen

Question 6

How can you prepare oxygen in the lab?

Answer 6

• Add hydrogen peroxide (H₂O₂) to a conical flask.
• Connect a bung with tubing to the top of the conical flask.
• Fill a trough with water
• Submerge two or three test tube in the water removing all the air from them
• Arrange each of them upside down filled with water- ready to bubble oxygen into them
• Remove the bung and add a small spatula of manganese dioxide (catalyst) and quickly replace the bung.
• Allow a small amount of bubbles to escape before you start collecting the pure oxygen by down ward displacement.

Question 7

What type of reaction is this?

2H₂O₂ –> 2H₂O + O₂

Answer 7

decomposition

A –> B + C

Question 8

What would you observe during the decomposition of hydrogen peroxide using the catalyst manganese dioxide?

Answer 8

Fizzing

manganese dioxide is not used up

Question 9

What is the name of the method used to collect oxygen druring the decomposition of hydrogen peroxide?

Answer 9

Downward displacement of water

Question 10

What is the test for oxygen?

Answer 10

glowing splint

relights

Question 11

How can you make carbon dioxide in a lab?

Answer 11

• Add a sample of CuCO₃ in a test tube.
• Add a bung and delivery tube to the end of the test tube
• Collect the carbon dioxide by upward displacement of air by placing the delivery tube into an upright test tube.

NOTE: CO₂ is more dense than air and will fill the test tube- pushing the air out.

Question 12

What is the test for carbon dioxide?

Answer 12

bubble through limewater

limewater turns cloudy

Question 13

Write the word equation for the reaction thermal decomposition of copper (II) carbonate

Answer 13

copper (II) carbonate –> copper oxide + carbon dioxide

Question 14

Write the word equation for the combustion of magnesium.

Answer 14

combustion means reaction with oxygen

magnesium + oxygen –> magnesium oxide

Question 15

What is the chemical equation for the thermal decomposition of copper (II) carbonate?

Answer 15

CuCO₃ –> CuO + CO₂

Question 16

What type of reaction is this?

2Ba + O₂ –> 2BaO

Answer 16

reaction with oxygen so it is called combustion or oxidation

Question 17

Why can’t we collect carbon dioxide by downward displacement of water?

Answer 17

Carbon dioxide is soluble in water- some of it will dissolve in the water

Question 18

What would you observe when you burn magnesium in oxygen?

Answer 18

grey solid turns to a white powder

very bright light

Question 19

How can we collect the gas carbon dioxide?

Answer 19

Upward displacement of air

CO2 is more dense than air and will fill an upright test tube- pushing (displacing) the air up and out.

Question 20

Is this reaction endothermic or exothermic?

Magnsium + oxygen –> magnesium oxide

Answer 20

exothermic - both heat and light are given off

Question 21

Write the word equation for the combustion of sulfur

Answer 21

sulphur + oxygen –> sulfur dioxide

Question 22

What would you observe if you plunge a metal oxide into water with a few drops of universal indicator?

Answer 22

The indicator will turn blue as metal oxides are alkaline

Question 23

Write the chemical equation for the combusiton of sulfur

Answer 23

S + O₂ –> SO₂

Question 24

What would you observe if a non-metal oxide were added to water with a few drops of universal indicator?

Answer 24

It would turn red

non-metal oxide in water forms an acid

H⁺ ions are present

Question 25

When sulfur burns in oxygen, what is the colour of the flame?

Answer 25

blue

Question 26

What are the three oxides which form in a car engine?

Answer 26

sulfur in fuel form sulfur dioxide nitrogen in air forms nitrous oxide carbon in fuel form carbon dioxide These all cause the rain to be acidic -acid rain

Question 27

What is the most abundance substance in air after nitrogen and oxygen?

Answer 27

argon

Question 28

List two gases which contribute to the greenhouse effect

Answer 28

carbon dioxide is a green house gas so is methane!!

Question 29

What is the percentage of nitrogen in air?

Answer 29

78%

Question 30

What is the percentage of oxygen in air?

Answer 30

21%

Question 31

When finding the percentage of oxygen in air copper turning are used. Why must the copper be in excess? (You have much more copper than needed for the reaction)

Answer 31

You are measuring the percentage of oxygen in air by reacting it with a metal. To get all the oxygen to react you need excess copper. When heated in air copper will turn from orange/pink to black as copper oxide is formed Eventually all the oxygen will be used up, allowing you to measure the remaining gases in air.

Question 32

Below are the results from the percentage of oxygen in air experiment using copper turnings * Starting volume 100 cm³ * End volume 79 cm³ Find the percentage of oxygen in air

Answer 32

(100 - 79) / 100 = 21%

Question 33

What is the valency of the hydroxide ion?

Answer 33

OH ^1-

Question 34

Describe the set-up for measuring the percentage of oxygen in air with copper turnings.

Answer 34

* Two syringes with glass tubing between. * Excess copper turnings placed in the middle of the tube. * Start with exactly 100 cm3 of air by reading the syringe volume at eye level. * Heat the glass tube under the copper turnings using a roaring flame. * Push the air from one syringe to another repeatedly until the volume no longer changes- all the oxygen has been used up. * Allow the gas to cool before reading the new volume of gas. * ((Starting volume - final volume) /starting volume) x 100= percentage oxygen in air

Question 35

What are the atoms in group 7 called?

Answer 35

Halogens

Question 36

What is the colour change of the copper turnings in the percentage of oxygen in air experiment?

Answer 36

orange/pink to black

Question 37

What is the valency of the sulfate ion?

Answer 37

SO4 ^2-

Question 38

Why do we need the gas to cool before taking the final volume reading in the percentage of oxygen in air experiment?

Answer 38

gas expands when heated. Fair test.

Question 39

What is the valency of the ammonium ion?

Answer 39

NH₄ ⁺

Question 40

Percentage of oxygen in air can be measured using the reaction of copper with oxygen or the reaction of iron wool and oxygen. What is the main difference with these two experiments?

Answer 40

Percentage of oxygen in air can be done **more quickly** using copper turnings. Copper is heated using a roaring flame. Percentage of oxygen in air is **much slower** (1-2 weeks) when using iron wool. Rusting is a very slow reaction.

Question 41

What are the elements in group 1 called?

Answer 41

Alkaline metals

Question 42

What is the valency of the carbonate ion?

Answer 42

CO3 ^2-

Question 43

What are the metals in group 2 called?

Answer 43

Alkaline Earth metals

Question 44

Name the only two elements which are liquid at room temperature

Answer 44

bromine and mercury

Question 45

What are the elements in group 0 called?

Answer 45

Noble gases

Question 46

What is special about the transistion metals?

Answer 46

They form colourful compounds They have more than one valency Fe²⁺ Fe³⁺

Question 47

Complete the reaction of iron with sulfur iron + sulfur --\>

Answer 47

iron + sulfur --\> iron sulphide

Question 48

Name the diatomic elements

Answer 48

Hydrogen Nitrogen Fluorine Oxygen Iodine Chlorine Bromine

Question 49

Name the compound NH₄OH

Answer 49

ammonium hydroxide

Question 50

Name the compound Na₂CO₃

Answer 50

sodium carbonate

Question 51

Name the compound MgSO₄

Answer 51

Magnesium sulfate

Question 52

Name the compound Ca(NO₃)₂

Answer 52

calcium nitrate

Question 53

Name the compound FeS

Answer 53

Iron sulfide

Question 54

A metal oxide which can dissolve in water will turn universal indicator __________________ because it is \_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_

Answer 54

A metal oxide which can dissolve in water will turn universal indicator **blue** because it is **alkaline**

Question 55

What does accurate mean?

Answer 55

close to the true value

Question 56

A non-metal oxide added to water will turn universal indicator ______________ because it is an \_\_\_\_\_\_\_\_\_\_\_\_

Answer 56

A non-metal oxide added to water will turn universal indicator **red** because it is an **acid** ## Footnote **SO₂ in water form H₂SO₄**

Question 57

What is an anamolous result?

Answer 57

A result which does not fit the pattern

Question 58

What should you do with an anamolous result?

Answer 58

record it but cross it out and carry out another reading- d**o not include it in an average**

Question 59

How should you measure the volume of a liquid in a measuring cylinder accurately?

Answer 59

* Place the measuring cylinder on a flat and level surface * Read the volume at eye level and the bottom of the meniscus

Question 60

Describe what a precise instrument is

Answer 60

An intrument that gives readings with more decimal places or an instrument with smaller increments (resolution) Some measuring cylinders read to +- 1 cm³ Some measuring cylinders read to +- 0.2 cm³

Question 61

What would the colour change be for the rusting of iron in the percentage of oxygen experiment?

Answer 61

grey to red/brown

Question 62

How do you know when reading are reliable?

Answer 62

When the readings are all very similar or clustered closely

Question 63

Name gases which contribute to the greenhouse effect

Answer 63

carbon dioxide and methane

Question 64

A dometic boiler is used to heat homes. It burns methane in oxygen. It has the following sign near the opening to the boiler. What does this sign mean in terms of combustion?

Answer 64

A **yellow flame** indicates that the flame is **not getting enough oxygen.** This means **incomplete combustion** is occuring which produces **carbon monoxide** Carbon monoxide is **toxic**

Question 65

Which letter/s show a pure element?

Answer 65

E, F and H Element contains only one type of atom.

Question 66

Which letter/s show a mixture of compounds

Answer 66

G Each substance contains two or more different atoms which are chemically bonded.

Question 67

Which letter/s show a mixture of elements?

Answer 67

B A mixuture contains two or more different substances which are not chemically bonded.

Question 68

Which letter/s show a pure compound?

Answer 68

A, D and I Compound is a substance containing two or more different atoms chemically bonded together.

Question 69

Which method would be suitable to collect carbon dioxide?

Answer 69

1st method- upward displacment of air Carbon dioxide is more dense than air. It will displace the air upward

Question 70

What gas is being produced in the following method? oxygen hydrogen carbon dioxide

Answer 70

carbon dioxide It is more dense than air and will displace air upward- or fall into the test tube.

Question 71

Which method would be suitable to collect hydrogen?

Answer 71

2nd method- downward displacement of air Hydrogen is less dense than air. It will rise into the container and displace the air downward

Question 72

Which method would be suitable to collect carbon dioxide?

Answer 72

1st method- upward displacment of air Carbon dioxide is more dense than air. It will displace the air upward

Question 73

Which method would be suitable to collect oxygen?

Answer 73

3rd method- downward displacement of water It has a similar density to air so method 1 or 2 will not work. Oxygen is less dense than water. It will bubble up into the tube displacing the water downward.

Question 74

**white phosphorus** can be used to measure the percentage of oxygen in air. - top is open, phosphorus is **touched with a hot metal rod**, top is closed - phosphorus burns in oxygen and water level rises. **What is the chemical equation for phosphorus burning in oxygen?**

Answer 74

4P _(s) + 5O_{2 (g)} ⇒ 2P₂O_{5 (s)}

Question 75

Wet iron wool can be used to find the percentage of oxygen in air - place wet iron filings in end of burette - turn upside down in water trough - close stopper - leave for several days **How do you know when all the oxygen has been used up?**

Answer 75

The water level no longer changes ## Footnote **This reaction is very slow so several days is needed plus excess iron**

Question 76

metal oxides are basic If they can dissolve in water, what will they form?

Answer 76

alkaline solution

Question 77

Non-metal oxides usually dissolve in water. What sort of solution do they form?

Answer 77

acidic solutions e.g. SO₂ in water forms sulfurous acid H₂SO₃