Chemical Changes

Question 1

Trends of metals in the periodic table

Answer 1

Reactivity of metals increase from top of a group to the bottom and from left to right (prominent in groupn1 and 2)

All form posiitve ions in reactions.

Question 2

Metal reaction equation with acid and water

Answer 2

Metal + Acid-> Salt + Hydrogen

Metal + water -> Metal hydroxide + Hydrogen

Question 3

Elemenst in reactivity series

Most reactive -> least reactive

Answer 3

Pottasium K
Sodium N
Lithium Li
Calcium Ca
Magnesium Mg
Carbon C
Zinc Zn
Iron Fe
Hydrogen H
Copper Cu

Question 4

What to metals appear as in the Earths surface (use equation)

Answer 4

As metal oxides (metal + Oxygen -> Metal Oxide)

Question 5

How are pure metals extracted

Answer 5

They are reduced (loses oxygen atoms / gains electrons) done by using electrolysis or reacted sith carbon

Elements more reactive then carbon go through electrolysis whereas those less reactive or reduced by a reaction with carbon

Question 6

Benefits of using reducing with carbon

Answer 6

Less expensive

Question 7

What do gold and platinum form as

Answer 7

They form as their own pure elemental form (unreactive)

Question 8

What is a redox reaction:

What is a reduction:

What is oxidisation:

Answer 8

Transfer of electrons between reactants

Reduction- Gain of electrons by an atom or ion (reduced charge) and a loss of oxygen

Oxidation- The loss of electrons by an atom or ion (increases charge) and gains oxygen atoms

Question 9

2Na + Cl2 -> 2NaCl find if this equation is a redox reaction

Answer 9

Sodium loses an electron to become complete
Chlorine gains an electron to be complete

Both elements changed oxidation state- redox reaction

Question 10

What do acids and bases form in aqeous solution

Answer 10

Acids form hydrogen (H+) ions in aqueous solution

Bases form hydroxide (OH-) ions in aqueous solutions

Question 11

What are alkali

Answer 11

Bases that are soluble. When a soluble base dissolved the resulting solution is alkaline

The more H+ ions produced in a solution =more acidic

More OH- ions produced in a solution = more alkaline it is

Question 12

What is the Ph scale

What does 0-6, 7 and 8-14 signify

Answer 12

Measures the acidity of a substance (concentration of H+ ions)-lower the value the higher the concentration

0 most acidic to least 6

7 neutral

8 least alkaline to most 14

Question 13

What can the Ph of a substance be measured by

Answer 13

Using a universal indicator- chemical mixtures that react with substances across a whole Ph range. Colour produced corresponding Ph level

Question 14

What happens to strong and weak acids in aqueous solutions

Answer 14

Strong acids are completely dissociate in an aqueous solution. Concentration of H+ ions will be high , low PH

Weak acids are only partially dissociated. Only a small proportion of molecule in the solution will dissociate into solution.

Question 15

How much does the PH decrease by every factor of 10 in the concentrationof H+ ions

Answer 15

As the concentration of H+ ions increases and strength of the acid, the PH will decrease

PH decreases by 1 for every increase of 10 in concentration of H+ ions

Question 16

Neutralisation reaction formula

Answer 16

Acid + Base –> Salt + water

Question 17

Why are weak acids reaction reversible

Answer 17

Ionisation of weak acids = reversible reaction, which sets up an equilibrium between the undissociated and dissociated acid.

Few acids release H+ ioms, equilibrium lies to the left

Question 18

Why are there confusion with strong acids and its concentration

Answer 18

The larger the amount of acid there is in a volume, the more concentrated it is.

You can have dilute (not concentrated) strong acid or concentrated but weak acid

Question 19

What do metals and metal hydroxides do

What are their formulas

Answer 19

They dissolve in water. These soluble compounds are alkalis .

Acid + Metal Oxide –> Salt + water

Acid + Metal Hydroxide –> Salt + Water

Question 20

What do metal carbonates do

What is the equation

Answer 20

They are also bases. They react with acid to produce salt,water and carbon dioixde

Acid + metal carbonate –> salt + water + carbon dioxide

Question 21

Required practical: Making soluble salts with insoluble bases

Answer 21

1) Pick the right acids and insoluble bases (insoluble metal oxide, hydroxide or carbonate)

2) Warm the dilute acid using a bunsen burner and turn it off

3) Add the insoluble bases to the acid a bit at a time until the reaction stops. Excess solid sinks when stirred

4) Filter out excess solid to get salt solution

5) Heat solution using a water bath to evaporate some of the water and stop to leave for cooling. Crystals of salt form which can be filtered and dried.

Question 22

Trends in reactivity series

Answer 22

The higher up in the reactivity series , the eaiser the metals forms positive ions

The higher up in the reactivity series, the more easily it reacts with water or acid

Question 23

How to investigate the reactivity of metals

How does magneisum,zinc and iron react with dilute acid

Answer 23

Speed of reaction indicated by the rate of hydrogen bubbles given off-measure the temp change of reaction over a period of time

Magnesium reacts vigorously with cold dilute acid.

Zinc react slowly

Iron reacts the slowest

Question 24

What are displacement reactions

Answer 24

Involves a metal kicking another metal out of a compound.

Reactive metal put inside a solution of a dissolved metal xompound , the reactive metasl will displace the less reactive metal in the compound

Question 25

What is an example of a displacement reaction

Answer 25

Iron + copper sulfate –> iron sulfate + copper

Fe(s) + CuSO4(aq) -> FeSO4(aq) +Cu(s)

Iron loses 2 electrons (2+ oxidised)

Copper gains 2 eledteons (-2 reduced)

1) metal ions reduced whereas the metal atom is oxidised

Question 26

What happens during electrolysis

Answer 26

An electric current is passed through an electrolyte (molten/dissolved ionic compound). The ions move towards the electrodes, where they react , the compounds dissolve

The positive ions in the electrolyte moves towards the cathode and gains electrons (reduced)

The negative ions in the electrolyte moves towards the anode and loses electrodes (oxidised)

This creates a flow of charge through the electrolyte as ions travel to electrodes. Ions form an uncharged element and are discharged from the electrolyte

Question 27

What is an electrolyte and electrode

Answer 27

Electrolyte: liquid or solution that conducts electricity

Electrode:A solid that conducts electricity when submerged in the electrolyte

Question 28

What happens to molten ionic compound during electrolysis

Answer 28

1)An ionic solid can’t be electrolysed because the ions are in fixed positions

2)Molten ionic compounds can be electrolysed because the ions can move freely and comduct electricity

3)Molten ionic liquids (lead/bromine) are always broken into their elements

Positive metal ions reduced to the element as a cathode(lead)

Negative non-metal ions oxidised to the element as an anode (bromine)

Question 29

Explain the process of electrolysis when extracting metals from their ores

Answer 29

Electrolysis used when metals more reactive then carbon= this method is expensive

Ores contains metals oxides such as aluminium oxide which has a very high melting point so is mixed with cryolite to lower the melting point

The molten mixture contaisn free ions- conducts electricity

Positive Al3+ ions attracted to the negative electrode where they each pick 3 electrons and turn neutral (aluminium atoms). These then sink at the bottom of the tank. Carbon reacts with oxygen in electrodes as carbon dioixde, carbon lost from the positive electrodes and must be replaced.

Negative O2- ions attracted to the posiitve electrode where it each loses two electrons. Neutral oxygen atons combine to form o2 molecules

Question 30

Electrolysis using an aqueous solution

Answer 30

1) In aqueous solutions there will be hdyrogen ions (H+) a d hydroxide ions (OH-) from the water.

2) At the cathode H+ ions and metal ions are present, hydrogen gas produced if the metal ions form an elemental metal more reactive then hydrogen.

If metal ions form elemental metal less reactive then hydrogen a solid layer of pure metal is produced

3) At the anode if OH- ions and halide ions (Cl-, Br-, I-) are present, molecules of halides formed.

If no halide ions are present, then the OH- ions are discharged and oxygen willl be formed.

4) This happens in aq solutions as water molecules break down molecules producing hydrogen ions and hydroxide ions that are discharged

Question 31

Req prac: Identifying products of electrolysis

1-3) what products are formed

4) How to set up equipment

Answer 31

1) when you electrolyse an aq solution, the products depend on the reactivity of the ions in the solution compared to H+ and OH- ions

2) At the cathode either a pure metal coating the electrode or bubbles of hydrogen gas produced

3) At the anode bubbles of oxygen gas produced unless halide ions are present

4) choose an electrolyte,

pour sample of electeolyte in a large beaker

immerse two inert electrodes into the solution and place inverted test tube over each

Connect electrodes to a power supply to electrolyse electrodes

Continue applying power until no more gas is produced in the test tubes

Question 32

How to test for different kind of gases

Chlorine

Oxygen

Carbon dixoide

Hydrogen

Answer 32

Chlorine: bleaches damp litmus paper turning it white

Oxygen: If you put a glowing splint inside, the oxygen will relight the splint

Carbon dixoide: Bubbling carbon dioxide through an aqueous solution of calcium hydroxude causes it to turn cloudy

Hydrogen: Hold a lit splint at the open end of the test tube containing hydrogen, squeaky pop.

Question 33

How can reactions of electrodes be represented by half equations

Answer 33

2H+ + 2e- —–> H2 (negative electrode)

4OH- —> O2 + 2H2O + 4e- ( )
or (Positive electrode)
4OH- - 4e- —> O2 + 2H2O. ( )