C7 Exothermic Reactions

Question 1

Complete word equation for reaction

Answer 1

Copper sulfate + water

Question 2

One observation during step 4 which shows copper carbonate is in excess

Answer 2

Residue of copper carbonate at the bottom of beaker

Question 3

Give 1 reason for filtering mixture in step 5

Answer 3

To remove excess copper

Question 4

Name equipment that can be used to warm filtrate gently in step 6

Answer 4

Bunsen burner

Question 5

Calculate mass of salt actually produced

Answer 5

92.8 = mass/12.5 x 100

0.928 x 12.5 = 11.6

Question 6

Give one reason why copper and metal is no used for sulfuric acid reactants

Answer 6

Copper - low reactivity, takes long to react

Sodium - high reactivity so reacts aggressively with sulfuric acid which is a hazard

Question 7

Give 1 similarity and one difference between electronic structures of sodium and potassium

Answer 7

Similarity - both have 1 electron in outer shell

Difference - sodium has 2 full shells, potassium has 3 full shells

Question 8

2 observations made when potassium reacts with water

Answer 8

Lilac flame

Potassium floats in water

Question 9

What colour is universal indicator when added to potassium hydroxide solution

Answer 9

Blue/purple

Potassium hydroxide has OH- so is alkali

Question 10

Estimate density of krypton

Answer 10

3.5-3.9

Question 11

Which combination of solutions produces a reaction when mixed

Answer 11

Chlorine and potassium bromide

Question 12

Which describes trend going down group 7

Answer 12

Molecular mass increases and boiling point increases

Question 13

Name models of atoms shown in figure 2

Answer 13

Plum pudding model

Nuclear model

Question 14

Compare plum pudding with atom today

Answer 14

Plum pudding has positive charge sphere - atom today as positive nucleus

Atom today has shells surround electrons

Atom today has neutrons, haven’t been discovered yet

Question 15

Isotopes

Answer 15

Same number of protons and electrons but different number of neutrons

Question 16

Explain results shown in figure 3

Answer 16

At 0g it is 21°C coz room temperature

Between 0g and 0.8g it increases as more zinc reacting

0.8g and 1g had same temp showing highest temp reached between these points

After 1g highest temp decreased as zinc in excess and solution gaining greater mass

Question 17

Why using polystyrene cup gives more accurate results than glass beaker

Answer 17

Polystyrene cup holds heat better causing heat output reaction to be more accurate

Question 18

Complete ionic equation between zinc and copper sulfate solution

Answer 18

Zn2+(aq) + Cu(s)

Question 19

1 reason for random errors in this experiment

Answer 19

Copper sulfate initial temp may be different

Question 20

Describe what happens to calcium atoms and chlorine atoms when ionic compound calcium chloride is formed

Answer 20

Calcium loses 2 electrons to form Ca2+

Chlorine gains 1 electron to form Cl-

These electrostatically attract to form calcium chloride

Question 21

Solid calcium chloride cannot be electrolysed

Give 1 reason why

Answer 21

Ions cannot flow and carry charge in a solid

Question 22

Name product formed at negative electrode calcium chloride electrolysed

Answer 22

Hydrogen

Question 23

What is half equation for reaction at positive electrode when calcium chloride solution electrolysed

Answer 23

2Cl- ————> Cl2 + 2e-

Question 24

Copper chromate solution contains the ions Cu2+ and CrO4 2-

Explain results shown

Answer 24

Copper is blue, chromate is yellow

Copper is positive ion so attracted to negative electrode

Chromate is negative ion so attracted to positive electrode

Question 25

Symbols the 5 metals in table 3 order of reactivity

Copper
Magnesium
Nickel
Silver
Zinc

Answer 25

Mg, Zn, Ni, Cu, Ag

Question 26

How hydrogen fuel cells produces a potential difference

Answer 26

Hydrogen lose electrons at anode

which flow through a circuit

Oxygen gains electrons at cathode forming water

Question 27

How iron conducts thermal electricity

Answer 27

Iron is transition metal metal so it’s delocalised electrons can carry thermal energy through metal

Question 28

Explain why mixing iron with other metals makes alloys harder than pure iron

Answer 28

Iron and other metals have different sized atoms meaning other metals distort irons layers which makes it harder for layers to slide over each other

Question 29

Correct equation for reaction iron reacts with chlorine

Answer 29

2Fe + 3Cl3 ————> 2FeCl3

Question 30

Ratio of numbers of ions in Fe3O4

Answer 30

1Fe2+ : 2Fe3+ : 4O2-

Question 31

Why propene has low boiling point

Answer 31

Has simple molecular structure meaning it has weak intermolecular forces that are easy to overcome

Question 32

Which is the correct reaction profile and labels for reaction between oxygen

Answer 32

B

Question 33

What is meant by weak acid

Answer 33

Acid that partially ionises in solution

Question 34

What happens to pH of an acid as acid is diluted with water

Answer 34

Concentration on H+ ions dcreases therefore neutralising acid

Question 35

Give 3 more steps the student must do before adding acid to alkali from burette

Answer 35

Use volumetric pipette to measure volume of alkali

Place alkali into conical flask

Add indicator

Question 36

Calculate volume of hydrochloric acid in cm3 needed in titration

Answer 36

0.0045 ➗ 0.15 = 0.3dm

0.03 x 1000 = 30cm

Question 37

Why calcium reacts more vigorously than magnesium with hydrochloric acid of same concentration

Answer 37

Calcium is more reactive than magnesium

Calcium’s outer electrons are further from nucleus, so attraction between nucleus and electron is weaker

This makes it easier for calcium to lose electrons and react

Question 38

Calculate mean temperature reached

Include an uncertainty in your answer

Answer 38

37.5 +- 3