Vocab - cScience

Question 1

What shape are bucky balls?

Answer 1

Spherical.

Question 2

Give one use of bucky balls.

Answer 2

Delivering drugs.

Question 3

Molecular formula of propanone.

Answer 3

C₃H₆O

Question 4

Why does propanone have a low boiling point?

Answer 4

Weak intermolecular forces.

Question 5

Explain why graphite is:

• A good electrical conductor.
• Soft and slippery.

Answer 5

Each carbon atom is covalently bonded to three others, leaving each atom with a free electron. This forms a sea of delocalised electrons, which are free to move and carry charge.
Graphite is soft and slippery because there aren’t any strong covalent bonds between the layers - the layers are instead held together by weak intermolecular forces, meaning they can easily slide over eachother.

Question 6

Isotope definition.

Answer 6

An isotope is a different form of an element with the same number of protons but a different number of neutrons.

Question 7

Calculate the Mr of gallium.

Answer 7

69.8

Question 8

Number of electrons and number of neutrons in gallium isotope.

Answer 8

31, 38

Question 9

What is the most likely formula of a gallium ion?

Answer 9

3+

Question 10

Give two reasons why the discovery of gallium helped Mendeleev’s periodic table to become accepted.

Answer 10

1) He predicted gallium’s properties before it was discovered.
2) He left a gap for it in the periodic table.

Question 11

Relative atomic mass of R.

Answer 11

96

Question 12

Atom economy equation.

Answer 12

(Mass of useful / mass of total reactants) x 100.

Question 13

Calculate the percentage atom economy for extracting tin in this reaction.

Answer 13

73%

Question 14

Evaluate possible methods for extracting tungsten from tungsten oxide.

Answer 14

You can’t use carbon to extract tungsten, because rather than displacing it from tungsten oxide, it reacts with tungsten to form tungsten carbide.
Hydrogen and iron both extract tungsten from it’s compound, but iron is cheaper than hydrogen, therefore iron should probably be used, as it produces tungsten solid and is cheap.

Question 15

Give two observations you could make when a small piece of potassium is added to water.

Answer 15

1) The metal floats and melts.

2) The metal lights on fire.

Question 16

Complete and balance the equation for the reaction of potassium with water.

Answer 16

2K + 2H₂O -> 2KOH + H₂

Question 17

Explain why the reactivity of elements changes going down group 1.

Answer 17

As you go down group 1, there are more electron shells. This means the electron on the outermost shell gets further and further away from the nucleus, which means there are weaker electrostatic forces of attraction between the nucleus and electron as you go down the group. This means that the electron is lost more easily, which shows it’s more reactive.

Question 18

Dot and cross diagram to show what happens when atoms of sodium and oxygen react to produce sodium oxide.

Answer 18

Na - one shell, one electron
Na - one shell, one electron
\+
O - one shell, six electrons
->
[Na - one shell, zero electrons] +
\+
[O - one shell, 6 crosses, 2 dots]

Question 19

Why is oxygen described as being reduced in the reaction between sodium and oxygen?

Answer 19

Because it gains one electron from each sodium atom (two in total).

Question 20

Explain why sodium oxide has a high melting point.

Answer 20

There’s strong electrostatic forces of attraction between the oppositely charged ions, which require a lot of thermal energy to overcome.

Question 21

Give one reason for:

• Step 2
• Step 5
• Step 6

Answer 21

2 - to speed up the reaction
5 - to ensure all of the substances have fully reacted
6 - to remove insoluble substances from the mixture

Question 22

How should filtrate be evaporated gently in step 7?

Answer 22

Heat the filtrate in an evaporating dish until crystals start forming.

Question 23

Calculate the volume of chlorine needed to react with 14g of iron.

Answer 23

9dm3

Question 24

Which substance could be a metal?

Answer 24

C

Question 25

Explain why alloys are harder than pure metals.

Answer 25

Because alloys are formed of many different metals, which makes the structure irregular - this makes it harder for the layers to slide over eachother. This means its stronger and harder than pure metals, which can slide over eachother.

Question 26

Describe a method the student could use to compare the reactivity of metal Q with that of zinc.

Answer 26

React metal Q with the silver nitrate solution and measure the temperature change of the reaction over a set period of time. Repeat with zinc and silver nitrate. By using the same mass and surface area each time, the more reactive the metal, the greater the temperature change.

Question 27

Explain the difference between the processes in electrolysis and in a chemical cell.

Answer 27

Chemical cells convert chemical energy into electricity, but electrolysis converts electricity into chemical energy.

Question 28

Bromine half equation.

Answer 28

2Br⁻ -> Br₂ + 2e⁻

Question 29

1) Copper nitrate - product at positive electrode.

2) Potassium iodide - product at positive and negative electrode.

Answer 29

1) Oxygen.

2) + : Iodine, - : Potassium

Question 30

Suggest why the blue colour of the copper nitrate solution fades during the electrolysis.

Answer 30

Because the copper concentration decreases.

Question 31

Number of atoms, moles, avogadro’s constant equation.

Answer 31

Number of atoms = moles x avo

Question 32

Determine the number of atoms of copper produced when copper nitrate solution is electrolysed for 20 minutes at a current of 0.6A (0.24g).

Answer 32

2.28 (3sf)

Question 33

Volume of oxygen required to react with 50cm3 of hydrogen sulfide.

Answer 33

75

Question 34

Bond energy of X.

Answer 34

532

Question 35

Suggest two improvements to the method that would increase the accuracy of the result.

Answer 35

1) Placing a white tile under the conical flask to see exactly when the colour changes.
2) Add the acid extremely slowly at the end and swirl after each addition to ensure the substances fully react.

Question 36

Calculate mass of ethanoic acid.

Answer 36

1.08g

Question 37

Conc of sodium hydroxide solution.

Answer 37

0.0576 mol/dm3