c4 - Chemical Changes

Question 1

What is the pH scale?

Answer 1

A measure of how acidic or alkaline solution is 1-14

Question 2

Examples of acids and alkalis

Answer 2

Acids-Acid, rain, vinegar, lemon juice, stomach acid
Alkali-Bleach drain cleaner soap

Question 3

What is an indicator? And a wide range one?

Answer 3

A dye that changes colour depending on whether it’s above or below a certain pH some contain mixture of dyes which gradually change colour wide range indicators useful for estimating pH of solution, e.g. universal indicator

Question 4

What is an acid?

Answer 4

A substance that forms aqueous solutions within less than a pH of, seven

Question 5

What is a base?

Answer 5

A substance, with a pH greater than seven

Question 6

What is an alkali?

Answer 6

A base that dissolves in water to form solution with a pH greater than seven

Question 7

What ions do acid form and what Ions do alkalis form in water?

Answer 7

Acids-H+
Alkali-OH-

Question 8

What do acids and bases do to each other and what is the equation for this?

Answer 8

Acids and bases neutralise each other
Acid+base—-> salt+water

Question 9

What is a pH meter and probe?

Answer 9

A pH probe attaches to a pH meter measures the pH electronically probe Goes into the solution and digitally displays the pH as a numerical value, making it more accurate than indicator

Question 10

What is the titration used for?

Answer 10

Is a method of analysing what the concentration of solution is . find out exactly how much of an acid is needed to neutralise a quantity of alkali vice versa

Question 11

State the steps of titration

Answer 11

1-Finding the concentration of alkali use a pipette and perfect filter, add a set volume of alkali to a conical flask, then add 2 to 3 drops of indicator
2. Use a funnel to fill the burette with acid of a known concentration do this below eyelevel in case acid falls. You don’t want to be looking up, so wear goggles record the initial volume of acid in the Burette
3. Add the acid from the burette into the alkali, a little bit at a time swirl the conical flask goes slower when endpoint ( colour change) is about to be reached indicator, changes colour when alkalis neutralised
4. Record the final volume of acid in the burette use it with initial reading to calculate the volume of acid used to neutralise the alkali

Question 12

How to increase the accuracy of titration

Answer 12

Spot any anomalous results
Several consistent readings
1st one should be a rough titration to get an approximate idea of where and point is
Repeat a few times, get pretty much the same answer each time within 0.1 cm³
Calculate the mean ignore any anomalous results

Question 13

Why should you use single indicators for titration?

Answer 13

Universal indicator, if you text me the pH of a solution and then the variety of colours
In titration we want to see a sudden colour change at the end. So we must use a single indicator like litmus or methyl

Question 14

What do acids do in aqueous solutions?

Answer 14

Ionise
produce H+, don’t produce H+ until meet water so hydrogen chloride gas is not acidic

Question 15

What is the difference between strong acids and weak acids in terms of ionisation?

Answer 15

Strong acids, such as sulphuric hydrochloric, nitric ionise completely and water all acid particles dissociate to release H+ ions
Weak acids Such as citric Carbonic economic, do not fully ionise in solutions, small proportion of acid particles to force you to release it, plus ions

Question 16

What are ionisation of weak acids able to do?

Answer 16

It’s a reversible reaction

Question 17

Why would strong acids be more reactive than weak acids of the same concentration?

Answer 17

If concentration of H+ ions is higher rate of reaction faster, so strong acid will be more reactive

Question 18

What is pH a measure of?

Answer 18

A measure of concentration of H+ ions in a solution

Question 19

For every decrease on the pH scale factor is the decrease

Answer 19

For every decrease of one of the pH scale, the concentration of H plus ions increases by factor of 10 PH4 has 10 times the concentration of H plus ions of ph 5 factor H plus ion concentration changes by 10 to the power of minus X X is difference in ph if it falls from 7 to 4 difference is -3 for 10 to the power of minus -3 equals 10 to the power of three

Question 20

What does the acid strength tell you?

Answer 20

What proportion of the acid molecules ionise in water

Question 21

What does the concentration of an acid tell you?

Answer 21

Concentration is different. How much acid is there for certain volume of water, how watered down acid is PH will decrease with increasing acid concentration, regardless if it is weak or strong 

Question 22

What is the connection between die dude strong acid concentrated weak acid

Answer 22

It can be delivered strong acid or a concentrated, but weak acid

Question 23

What is the name given to some of the metal oxides and metal hydroxides that dissolve in water?

Answer 23

These soluble compounds are called alkalis that react with acids to neutralise reactions

Question 24

What are the equations for alkalis reacting with acids?

Answer 24

Acid+ Metal oxide——-> salt + water
Acid+Metal hydroxide ——> salt + water

Question 25

How do we name the salt created?

Answer 25

First name is name of metal and surname is acid name hcl plus copper oxide is copper chloride 

Question 26

What is the equation for when metal carbonate react with acids?

Answer 26

Metal carbonate that also bases acid plus metal carbonate—->salt + water+ carbon dioxide

Question 27

Say the steps of crystallisation

Answer 27

1. Pick a suitable acid and insoluble base 2. Gently warm dilute acid, using Bunsen burner, then turn it off 3. Add into your base to acid a bit of time until normal reacts. You know when acid is neutralised because even after stirring excess solid new sink to the bottom 4. Then filter out excess solid to get salt solution 5. For pure solid crystals of salt, gently heat solution, using water, bath or heater to evaporate some water to make it more concentrated stop heating leave it to cool crystals of salt and form. These can be filtered out of the solution then dried

Question 28

What is the reactivity series and what decided reactivity of metal

Answer 28

An ordered list of metals based on reactivity towards other substances. how easily they lose electrons to form positive ions higher of the reactivity series more easier. The form positive ions metals react with water acid did lose electrons to form plus ions higher metal on reactivity series, more easily reacts with water acid. 

Question 29

State the order of the reactivity series

Answer 29

Potassium, K. Sodium, NA Lithium, LI Calcium Ca Magnesium Mg Carbon C Zinc Zn Iron Fe Hydrogen H Copper Cu Potassium-calcium=very reactive Magnesium-iron=fairly reactive Hydrogen-copper=not very reactive

Question 30

What is the equation for when acid and metal react How do we see the root of this reaction?

Answer 30

Acid + metal ——-> salt +hydrogen gas Speed reaction indicated burrito much because of hydrogen gas given off More reactive than metal faster the reaction Copper won’t react with dilute acids Magnesium react vigorously w them

Question 31

What is another way of checking the reactivity of the metal?

Answer 31

Measure Temperature change of reaction, if you use a mess and surface area of metal each time than more reactive, the metal grater a temperature change

Question 32

State the equation, metal and water

Answer 32

Metal + water ——> metal hydroxide +hydrogen Potassium, sodium, lithium, calcium, react with water Zinc, iron copper won’t react with water

Question 33

What is a metal ore

Answer 33

Created one common metals, such as iron reacts with oxygen to form oxides (oxidation) . need to be extracted. Reaction that separates metal from its oxide is called reduction

Question 34

Define oil rig

Answer 34

Oxidation is a loss of electrons or gain of oxygen. Reduction is the gain of electrons or loss of oxygen

Question 35

When can a metal be extracted using reduction using carbon?

Answer 35

Who is reduced as oxygen is removed carbon gains oxygen so it’s oxidised metal is higher than Corbin are extracted using electrolysis which is expensive metal be low carbon extracted by reduction using carbon. Iron oxide is reduced in the blast furnace

Question 36

State the metals that are found in the Earth by themselves (elemental form)

Answer 36

Gold silver platinum bronze, these are so reactive

Question 37

What is a redox reaction?

Answer 37

When reduction and oxygen take place at the same time

Question 38

What is a displacement reaction?

Answer 38

When a more reactive metal will displace a less reactive metal from its compound eg iron displaces copper

Question 39

Write a half equations and explain what is going on in the definition of reaction between copper sulphate and iron

Answer 39

fe——> fe2+ + 2 e-s iron looses 2 electrons to become a 2+ ion Oxidised Cu2+ + 2 e-s ——-> cu Copper iron gangsta electrons to become copper atom reduced

Question 40

What happens to metal ions and metal atoms in terms of oxidisation and reduction?

Answer 40

Metal ion gains electrons and is reduced to metal at the movies loses electrons and is oxidised

Question 41

What is special about Ionic equations

Answer 41

Only particles that react and products they form are shown Spectator ions don’t change, so no need to include them only right to substances that reduce oxidised

Question 42

How does electrolysis work?

Answer 42

Uses electrical current to cause a reaction. This current is passed through the electrolyte ( molten or dissolved compound) . The ions move towards the electrodes, where they react and the compound decomposes.

Question 43

Define panic

Answer 43

Positive ions move towards the cathode (negative electrode) And gain electrons (reduced) Negative ions move towards the anode (positive electrode) And lose electrons (Oxidised) They become discharged

Question 44

Explain why molten ionic compounds can be electrolysed but ionic solids can’t

Answer 44

Ionic solid, can’t be electrolysed since ions and fix positions and can’t move Molten ionic compounds can be electrolysed ions can move freely and conduct electricity

Question 45

What are the problems with using electrolysis to extract metals?

Answer 45

Very expensive, lots of energy required to melt ore and produce required current

Question 46

What will happen to positive aluminium ions and negative oxygen ion and electrolysis

Answer 46

Aluminium positive ions attracted to negative electrode pick up 2 electrons each neutral atoms sink to bottom Negative oxygen ions attracted to positive electrode loses two electrons, each neutral atom, combine to form O2 molecule

Question 47

What are the anode made of?

Answer 47

Carbon , so they need to be replaced regularly sincere react with O2 to produce CO2

Question 48

What is different about Aqueous solutions to do with ions?

Answer 48

As well as ions there will also be hydrogen ions (H+) And hydroxide ions (OH-) From the water

Question 49

What happened at the catfood if H plus ions and metal ions are present

Answer 49

If the elemental metal is more reactive than hydrogen and hydrogen gas is produced if less reactive element of metal produced a solid layer of pure metal produced instead

Question 50

What happened at the anode it OH minus ions and halide ions are present

Answer 50

If both present molecules of chlorine, bromine or iodine will be formed if no halide, ions, present oH minus ions discharge, and oxygen will be formed

Question 51

How would we work out what gas has been produced?

Answer 51

Test, gaseous products Chlorine bleach is a damp,litmus paper, turning it white. Hydrogen makes a squeaky pop with a lighted splint. Oxygen will relight a glowing splint

Question 52

What should you draw when during electrolysis reaction?

Answer 52

Power supply lamp label everything

Question 53

What should be the same for you? Trafficway Asian give examples of half equations.

Answer 53

Number of electrons needs to be seen for half equation Negative electrode:2H+ +2e- ——> H2 Positive electrode: 2cl- ——> cl2 + 2 e- Ionic equation:2H+ +2Cl- ——> H2 + Cl2