P1 - Chemical Change

Question 1

What is the range of the pH scale ?

Answer 1

0-14, the lower the pH of a solution the more acidic it is and the higher the pH the more alkaline it is. With neutral substances having a pH of 7.

Question 2

What colour should acids change a universal indicator ?

Answer 2

Yellow to orange to red (red being strongest acidity).

Question 3

What colour should alkalis change a universal indicator ?

Answer 3

Blue to purple (purple being strongest alkalinity)

Question 4

How can you measure the pH of a solution ?

Answer 4

Using an indicator which changes colour depending on whether its’ above or below a certain pH, Universal indicator (wide range indicator) to estimate the pH of a solution or a pH probe attached to pH meter to measure the pH of solutions electronically showing pH as a number.

Question 5

What ions do acids form in water ?

Answer 5

H+ ions.

Question 6

What ions do alkalis form in water ?

Answer 6

OH- ions.

Question 7

What are alkalis ?

Answer 7

Bases that dissolve in water to form a solution.

Question 8

What products are formed when you react together an acid and a base ?

Answer 8

A neutralisation reaction forms a salt and water (acid + base –> salt + water).

Question 9

What is formed in the neutralisation reaction between acids and alkalis ?

Answer 9

H+(aq) + OH-(aq) –> H20.

Question 10

What is a titration ?

Answer 10

Method of analysing concentrations of solutions, you can use it to find what volume of acid you need to neutralise a measured volume of alkali, and then using this work out their concentrations.

Question 11

How can you do titration ?

Answer 11

Use a pipette and set a volume of the alkali in a conical flask and add two-three drops of indicator, use a funnel to fill a burette with some acid of a known concentration and record this initial volume. Use the burette to add the acid to to the alkali a bit at a time giving the conical flask regular stirs, the phenolphthalein indicator should go from pink (in alkaline conditions) to colourless (in acidic conditions). Record the final volume of acid in the burette and calculate the volume of acid used to neutralise the alkali.

Question 12

Why would you repeat titrations ?

Answer 12

To find a mean volume, the first titration should be a rough one to get an approximate idea of where the solution changes colour. you then need to repeat it to get the same approximate answer each time (within 0.10 cm^3). Calculate the mean of the results excluding anomalous ones.

Question 13

What are some common single indicators ?

Answer 13

Phenolphthalein, litmus and methyl orange.

Question 14

What colours can a phenolphthalein indicator go ?

Answer 14

It’s colourless in acids and pink in alkalis.

Question 15

What colours can a litmus indicator go ?

Answer 15

It’s red in acids and blue in alkalis.

Question 16

What colours can a methyl orange indicator go ?

Answer 16

It’s red in acids and yellow in alkalis.

Question 17

What do acids do in an aqueous solution ?

Answer 17

They ionise in aqueous solution, producing protons (H+ ion is just a proton) .

Question 18

What do strong acids do in water ?

Answer 18

They ionise completely, all the acid particles dissociating to release H+ ions (HCl –> H+ + Cl-

Question 19

What do weak acids do in water ?

Answer 19

They don’t fully ionise in solution, only a small proportion of acid particles dissociate to release H+ ions. The ionisation of a weak acid is a reversible reaction, which sets up an equilibrium between the undissociated and dissociated acid, and since only a few acids particles release H+ ions the equilibrium lies to the left. (CH3COOH H+ + CH3COO-)

Question 20

What does the pH actually measure ?

Answer 20

The concentration of H+ ions in the solution, for every decrease in 1 on the pH scale the concentration of pH ions has increased by a factor of 10.

Question 21

What is the formula for the factor change of H+ ions ?

Answer 21

Factor H+ ion concentration changes by = 10^-x (x = difference in pH)

Question 22

What are bases ?

Answer 22

Soluble compounds, metal oxides and hydroxides and metal carbonates, that react with acids in neutralisation reactions.

Question 23

What is formed in a reaction between an acid and a metal carbonate ?

Answer 23

Salt, water and carbon dioxide.

Question 24

What is formed in a reaction between an acid and a metal oxide or metal hydroxide ?

Answer 24

Salt and water.

Question 25

How can you make a soluble salt using an insoluble base ?

Answer 25

Pick the right acid and insoluble base to make the salt you want, gently warm dilute acid and add the insoluble base until no more reacts - you’ll know when this happens because the excess base will just sink. Filter out this excess solid to get salt solution, gently heat solution to evaporate some water and then let it cool. Crystals of salt should form, which can be filtered out and dried - cystalisation reaction.

Question 26

What is the reactivity series ?

Answer 26

List of metals in order of their reactivity towards other substances.

Question 27

What determines a metals reactivity ?

Answer 27

How easily they lose electrons and form positive ions, the higher up the reactivity series a metal is the more easily it forms positive ions.

Question 28

What is in the reactivity series in order of most to least reactive ?

Answer 28

Potassium(K), sodium(Na), lithium(Li), calcium(Ca), magnesium(Mg), carbon(C), zinc(Zn), iron(Fe), hydrogen(H) and copper(Cu)

Question 29

Why is carbon included in the reactivity series ?

Answer 29

Gives information about how metals will react with it, metals less reactive than carbon can be extracted from their ores by reduction with carbon, but metals more reactive cannot be extracted this way.

Question 30

Why is hydrogen included in the reactivity series ?

Answer 30

Gives information about how metals will react with it, metals more reactive than hydrogen will react with acids, but metals less reactive will not react with acids.

Question 31

What does a reaction between a metal and acid produce ?

Answer 31

A salt and hydrogen.

Question 32

What determines the speed of the reaction between a metal and acid ?

Answer 32

The reactivity of the metal, the more reactive the faster, metals like copper won’t react with cold dilute acids. You can measure the speed of the reaction by looking at the rate at which bubbles of hydrogen are given off.

Question 33

What does a reaction between a metal and water produce ?

Answer 33

A metal hydroxide and hydrogen.

Question 34

What metals react with water ?

Answer 34

Metals high on the reactivity series; potassium, sodium, lithium and calcium, but not ones lower down such as zinc, iron or copper.

Question 35

What is oxidation ?

Answer 35

The gain of oxygen, and how metal ores are formed. It can also be the loss of electrons.

Question 36

What is reduction ?

Answer 36

The loss of oxygen, and how metals are extracted from their ores. It can also be the gain of electrons

Question 37

How can some metals be extracted from their ores ?

Answer 37

Chemically by reduction using carbon, where the ore is reduced as oxygen is removed and carbon gains oxygen so is oxidised. This only works if the metal is lower than carbon on the reactivity series.

Question 38

How can metals higher than carbon on the reactivity series be extracted from their ores ?

Answer 38

Using electrolysis - which is expensive.

Question 39

P

Answer 39

98