Topic 4- Chemical Changes.

Question 1

what is the pH scale from?

Answer 1

0-14

Question 2

what does the pH scale measure?

Answer 2

it measures how acidic or alkaline a solution is.

Question 3

the pH scale?

Answer 3

the lower the pH of a solution, the more acidic it is. the higher the pH of a solution, the more alkaline it is. a neutral substance (pure water) has pH 7.

Question 4

how to measure the pH of a solution?

Answer 4

dye that changes colour (whether its above or below a certain pH). it is useful for estimating the pH of a solution. it has a wide range substances.

Question 5

what is an example to measure the pH of a solution?

Answer 5

• universal indicator is a wide range indicator. it gives the colours.
• a pH probe attached to a pH meter- electronically. the probe is put in the solution and the pH is shown as a number. this means it’s more accurate than an indicator.

Question 6

what neutralises each other?

Answer 6

acids and bases. bases are greater than 7.

Question 7

what happens when acids dissolve in water?

Answer 7

they form solutions with a pH of less than 7. acids form H+ ions in water.

Question 8

what are alkalis?

Answer 8

they are bases that dissolve in water to form solutions with a pH greater than 7- form OH- ions. its a soluble metal hydroxides.

Question 9

what is neutralisation?

Answer 9

reaction between acids and bases. shown using H+ and OH- ions. products with a pH of 7 is neutral.

Question 10

what can you do to neutralising?

Answer 10

• you can add an indicator to the acid or alkali. then gradually add the other substance. the indicator will change colour when the neutralisation reaction is over.
• if you use universal indicator, add the substance until the universal indicator is green, this is when the pH of the solution is neutral.

Question 11

what metals react with each other?

Answer 11

metal oxides and metal hydroxide react with each other in neutralisation reactions to form a salt and water. the salt forms depends upon the acid and the metal ion in the oxide or hydroxide.

Question 12

reactions…

Answer 12

• HCI reacts to form chlorides,
• H2SO4 reacts to form sulfates.
• HNO3 reacts to form nitrates.

Question 13

what does acids and metal carbonates produce?

Answer 13

it produces carbon dioxide. metal carbonates are bases, they react with acids to produce a salt, water and carbon dioxide.

Question 14

what happens when you react acid with an insoluble base or a metal?

Answer 14

you make a soluble salt.

Question 15

what is a reactivity series?

Answer 15

it is a list of metals in order of how reactive they are.

Question 16

what does metal form when they react?

Answer 16

they form positive ions.

Question 17

what does reactivity depend on?

Answer 17

on how easily they lose electrons and form positive ions. the higher it is on the series the easier they form positive ions.

Question 18

what other non-metals are often on the list?

Answer 18

• carbon.

- hydrogen.

Question 19

what do metals react to form?

Answer 19

they react with oxygen to form oxide.

-example of oxidation- often the ores that the metals are removed from.

Question 20

what is reduction reaction?

Answer 20

it is a reaction that separates a metal from its oxide. copper oxide is reduced to copper.

Question 21

what is oxidation?

Answer 21

it is a gain of oxygen. magnesium is oxidised to make magnesium oxide.

Question 22

what can some metals be extracted from?

Answer 22

from their ores using a reaction with carbon. this reaction, the ore is reduced as oxygen is removed from it. carbon gains oxygen so it is oxidated.
-for example: iron (III) oxide + carbon —> iron + carbon dioxide. 2Fe 2O3 + 3C —> 4Fe _3CO2.

Question 23

what can the reactivity series tell you?

Answer 23

if a metal can be extracted with carbon. metals above carbon are extracted using electrolysis (used to extract metals that react with carbon). this is expensive as it takes lots of energy to melt the ore and produce electricity. metals below carbon can be extracted by reduction using carbon. iron oxide is reduced in a blast furnace to make iron. this is because carbon can only take the oxygen away from metals which are less reactive than carbon itself.