Chemical Reactions

Question 1

4 types of chemical reactions

Answer 1

1. Combination
2. Decomposition
3. Single displacement
4. Double displacement

Question 2

Combination Reaction

Answer 2

2 or more elements/compounds combine to form one product’

A + X -> AX

Question 3

3 combination reaction examples

Answer 3

1. Magnesium + Oxygen -> magnesium oxide
   - 2Mg + O2 -> 2Mgo
   magnesium combines with oxygen to form magnesium oxide
2. Hydrogen + oxygen -> water
   - 2H2 + O2 -> 2H2O
   hydrogen gas and oxygen gas combine to form water
3. Iron + sulfur -> iron (III) sulfide
   - Fe + S -> FeS
   metal iron combines with sulphur power to form iron (III) sulfide

Question 4

Decomposition Reaction

Answer 4

One substance split to form 2 or more substances

AX -> A + X

Question 5

Magnesium Combustion Experiment method

Answer 5

1. measure mass of crucible without lid
2. clean strip of magnesium with sandpaper until shiny
3. coil magnesium strip and place into crucible
4. measure the mass of magnesium strip and crucible without its lid
5. heat crucible in tripod with bunsen burner on blue flames for 5 minutes
6. let the crucible cool down and measure its mass again without lid

Question 6

Magnesium combustion reaction: Why was the mass of the product different to the mass of the reactant (magnesium strip)?

Answer 6

• the mass of the product magnesium oxide was greater since it combined the mass of the magnesium and oxygen used in the reaction
• total mass of all reactants and products remained the same, but the mass of oxygen used in the reaction was not recorded
• law of conservation of mass: total mass of reactants in a chemical reaction will equal the total mass of the products after the reaction

Question 7

Magnesium combustion reaction: Were there any other sings that a chemical reaction took place during this experiment?

Answer 7

• change in mass
• glowing white light
• magnesium strip changed color
  shiny magnesium strip became a white powder

Question 8

4 Decomposition reaction examples
- copper carbonate
- electrolytic decomposition
- thermal decomposition
- photolytic decomposition

Answer 8

1. Copper carbonate -> copper oxide + carbon dioxide
   CuCO3 -> CuO + CO2
   Copper carbonate on heating decomposes into solid copper oxide and carbon dioxide gas

Electrolytic decomposition
2. Water -> hydrogen + oxygen
2H20 -> 2H2 + O2
Liquid water on passing electric current decomposes into hydrogen gas and oxygen gas

Thermal decomposition
3. Sodium Bicarbonate -> sodium carbonate + water + carbon dioxide
NaHCO -> Na2CO3 + H2O + CO2
Baking soda decomposes with heat

Photolytic decomposition
4. Hydrogen peroxide -> water + oxygen
H2O2 -> H2O + O2
Hydrogen peroxide breaks down when exposed to UV light

Question 9

Single displacement Reaction

Answer 9

An element (like metal) react with a compound and replaces another element from its compound

A + BX -> AX + B
solid/pure element + aqueous -> aqueous + solid

Question 10

4 Single Displace reaction examples
- metal displacement zinc + copper sulfate
- metal displacement copper+ silver nitrate
- hydrogen displacement magnesium + hydrochloric acid
- hydrogen displacement zinc + hydrochloric acid

Answer 10

1. Zinc + copper sulfate -> Copper + Zinc sulfate

when zinc strip is placed in copper sulfate solution, copper solid and solution of zinc sulfate are formed

2. Copper + Silver nitrate -> silver + copper nitrate

when copper wire is placed in dissolved silver nitrate solution, crystals of silver and solution of copper nitrate are formed

3. Magnesium + Hydrochloric acid -> Hydrogen + Magnesium chloride

when magnesium metal is placed in hydrochloric acid, hydrogen gas and magnesium chloride solution

4. Zinc + Hydrochloric acid -> Hydrogen + Zinc Chloride

when zinc metal is placed in hydrochloric acid, hydrogen gas and zinc chloride solution

Question 11

Reactivity series

Answer 11

Reactivity is the arrangement of metals in the descending order of their reactivities

Question 12

Reactivity of metals depends on what?

Answer 12

It depends on how easily they give up their outer shell electrons

Question 13

Acronym for reacitivity series

Answer 13

Please stop calling me a careless zebra, instead try learning how copper saves gold

Question 14

Single Displacement reaction: method

Answer 14

Different metal pieces added to test tube of different nitrate solutions

Question 15

Single Displacement reaction: All the solutions used in these reactions were nitrates. Why did this make the experiment fair?

Answer 15

the presence of nitrate anions in each aqueous solution acts as the controlled variable.

the nitrate anions are kept constant in each solution so that the results are fair and accurate as the independent variable is the type of metal rod placed in each solution.

to ensure there is no other variable that will impact the result of what we are investigating

Question 16

Single Displacement reaction: Why did this make the experiment fair?

Answer 16

The aim of the experiment was met and the reactivity of each metal could be determined into a reactivity series

Question 17

Double displacement reaction
- what must reactants be?
- what switches?

Answer 17

when ions of 2 compounds exchange places with each other

AB + CD -> AC + CB
aq + aq -> s? + aq

• reactants are 2 IONIC compounds, products are 2 NEW compounds
• swapping cations or anions

Question 18

Precipitation reaction

Answer 18

Specific type of double displacement reaction where 2 aqueous solutions reaction to form one solid precipitate and an aqueous solution

Question 19

What can be used to predict precipitation reactions?

Answer 19

Solubility rules/tables to decide whether a precipitate will form

low solubility = form a precipitate

Question 20

What do more reactive elements do?

Answer 20

More reactive elements will replace less reactive elements in a compound

Question 21

chemical reaction meaning

Answer 21

rearranging atoms to create new substances

Question 22

acid base reactions meaning

Answer 22

type of chemical reaction where an acid and base react to create water and salt

acid + base -> water + salt

Question 23

Acid

Answer 23

• aqueous solution
• pH lower than 7 (0-6 pH)
• blue litmus paper turns red
• corrosive
• sour taste

e.g. hydrochloric acid HCI, sulphuric acid H2SO4, nitric acid HNO3

Question 24

What do acids produce?

Answer 24

acids produce hydrogen ions (H+) in solution

the more hydrogen ions produced, the more acidic it is and the lower the pH

Question 25

Base

Answer 25

- aqueous solution - pH higher than 7 (8-14pH) - red litmus paper turns blue - caustic - bitter taste e.g. sodium hydroxide NaOH, potassium hydroxide KOH, lithium hydroxide LiOH

Question 26

What do bases produce?

Answer 26

bases produce hydroxide ions OH- in solution the more hydroxide ions produced, the more basic it is, and the higher the pH

Question 27

Water

Answer 27

water is neutral, it is not acidic or basic, it has a pH of 7

Question 28

Acid- base reactions are called what?

Answer 28

neutralisation reactions (double displacement) since water is made e.g. H+ + O- = H2O

Question 29

Conservation of Mass

Answer 29

Mass cannot be created or destroyed in a chemical reaction, only transformed. the total mass of the reactants before a chemical reaction equals the total mass of the products after the reaction

Question 30

hydrochloric acid + sodium hydroxide -> ? explain!

Answer 30

sodium chloride + water HCL + NaOH -> H2O + NaCL the hydrogen ion from acid, and hydroxide ion from the base combine to create water!

Question 31

hydrochloric acid + lithium hydroxide ->

Answer 31

water + lithium chloride

Question 32

nitric acid + potassium hydroxide

Answer 32

potassium nitrate + water

Question 33

Precipitation demo practical: identify what the expected results for lead nitrate and potassium iodide

Answer 33

lead nitrate and potassium iodide reacts to form potassium nitrate and lead iodide the lead iodide will form a precipitate and the potassium nitrate will remain aqueous according to the law of conservation of mass, the total mass of the reactants should be the same as the total mass of products

Question 34

Acid-metal reactions are what type of reaction?

Answer 34

single displacement reaction!

Question 35

hydrochloric acid + sodium ->

Answer 35

hydrogen + sodium chloride when reactive metals are put into acid, bubbles are formed!

Question 36

Acid-metal reaction

Answer 36

an acid and reactive metal react to create hydrogen gas and salt e.g. hydrochloric acid + sodium -> hydrogen + sodium chloride - metals more reactive than hydrogen will displace it from the solution (acid) to form a new solution (salt). hydrogen gas is then formed

Question 37

Acid carbonate reactions

Answer 37

an acid and carbonate react to create water, salt and carbon dioxide gas

Question 38

Hydrochloric acid + calcium carbonate ->

Answer 38

calcium chloride + carbon dioxide + water

Question 38

Why is cleaning up acid spills with carbonates safer than using a base (neutralization reaction) or metal (acid-metal reaction)

Answer 38

strong, caustic BASE neutralization reaction would be required to clean up a strong acid highly flammable hydrogen gas would be produced if a metal (acid metal reaction) was used to clean up an acid A carbonate reacts with acid which is gentler and safer. No harmful base and no flammable gas.