C2.1-Atoms and Reactions

Question 1

C2.1.1-What is an Isotope?

Answer 1

An isotope is an atom of an element with the same amount of protons but a different amount of neutrons.

Question 2

C2.1.1-What is the atomic structure and their charges?

Answer 2

The atom consists of a nucleus made up of protons and neutrons with electrons around the nucleus in shells.
Proton: +1 charge, 1 mass, Neutron: 0 charge, 1 mass, Electron: -1 charge, 1/1836th mass of proton

Question 3

C2.1.1-What are chemical and physical differences in isotopes?

Answer 3

Different isotopes of the same element have the same number of electrons and therefore react in the same way as neutrons don’t have an effect on the reaction. There may be different physical properties as higher mass isotopes will have a higher melting point, boiling point and density.

Question 4

C2.1.1-What is relative isotopic mass?

Answer 4

Relative isotopic mass is the mass of an isotope relative to 1/12th the mass of a carbon-12 atom.

Question 5

C2.1.1-What is Relative atomic mass?

Answer 5

Relative atomic mass is the weighted mean mass of an atom of an element relative to 1/12th the mass of a carbon-12 atom.

Question 6

C2.1.1-How does a mass spectrometer work?

Answer 6

A sample is placed in the mass spectrometer and it is vaporised and then ionised to from positive ions.
The ions are accelerated, heavier ions move more slowly and are more difficult to deflect than lighter ones so ions of each isotope are separated.
The ions are detected on a mass spectrum as a mass to charge ratio.

Question 7

C2.1.2-What are some of the polyatomic ions?

Answer 7

Polyatomic: NO3-, CO3(2-), SO4(2-), OH-, NH4+,
Others: Zn2+, Ag+

Question 8

C2.1.2-What are diatomic molecules?

Answer 8

Two atoms bonded together.
H2, N2, O2, F2, Cl2, Br2, I2.

Question 9

C2.1.3-What is amount of substance?

Answer 9

Quantity used to count the number of particles in a substance measured in a unit called mole.

Question 10

C2.1.3-What is a mole and the Avogadros constant?

Answer 10

One mole is the amount of substance that contains 6.02x10^23 particles. The Avogadros constant is 6.02x10^23 mol^-1 which is the number of particles in each carbon-12 mole.

Question 11

C2.1.3-What is molar mass and molar gas volume?

Answer 11

Molar mass(g/mol^-1) is the mass per mole of a substance. Molar gas volume(Vm) is the volume per mole of gas molecules at a stated temp and pressure.

Question 12

C2.1.3-What is hydrous?

Answer 12

A substance that contains water, either in its structure or as water of crystallisation.

Eg: Hydrated Copper(II) Sulfate(CuSO4 - 5H2O is blue because it has water of crystallisation

Question 13

C2.1.3-What is anhydrous?

Answer 13

A substance that doesn’t contain water or water of crystallisation.
Eg: Anhydrous Copper(II) Sulfate(CuSO4) is white because it lacks water molecules.

Question 14

C2.1.3-What is Water of Crystallisation?

Answer 14

Water molecules that are chemically bonded within the crystalline structure of a compound.

Eg: CuSO4 - 5H2O, the 5H2O molecules are water of crystallisation.

Question 15

C2.1.3-How can a salt go from hydrous to anhydrous?

Answer 15

When blue crystals of hydrated copper(II) sulfate are heated, bonds holding the water within the crystal are broken off which drives the water off.

Question 16

C2.1.3-How to carry out experiment that determines water of crystallisation in hydrated crystals?

Answer 16

Weigh an empty crucible. Add the hydrated salt into the weighed crucible and weigh the crucible and hydrated salt. Use a pipe clay triangle to support the crucible containing hydrated salt on the tripod. Heat crucible and contents gently for 1 min, then heat strongly for 3 mins. Leave crucible to cool and then weigh the crucible and anhydrous salt.

Question 17

C2.1.3-What calculations are needed for Water of Crystallisation experiment?

Answer 17

Use mass values to find the mass of anhydrous salt and then find the moles with moles = mass(g)/mr. Then use mass values to find mass of water and find moles of water. Find smallest whole umber ratio and write formula down. (CuSO4 - 5H2O)

Question 18

C2.1.3-What assumptions are made about the Water of Crystallisation experiment?

Answer 18

If hydrated and anhydrous salt have different colours, you can be sure when all water is removed. However if a similar colour, heat the crystals until mass of residue no longer changes suggesting water is removed. Many salts decompose further when heated such as copper(II) Sulfate decomposing to form black copper(II) oxide.

Question 19

C2.1.3-List measurement conversions

Answer 19

cm^3 to m^3 — X 10^-6
dm^3 to m^3 — X 10^-3
C to K — +273
kPa to Pa — X 10^3

Question 20

C2.1.3-How to find relative molecular mass

Answer 20

Add a sample of the volatile liquid to a small syringe via needle and weigh small syringe. Inject sample into a gas syringe through self sealing rubber cap. Reweigh the small syringe to find the mass of the volatile liquid added to the gas syringe. Place the gas syringe in a boiling water bath at 100 degrees. The liquid vaporises producing a gas and pressure is recorded. Then use pV=nRT to find moles and then mr.

Question 21

C2.1.3-What are balanced equations used for?

Answer 21

They’re used to find the quantities of reactants required to prepare a required quantity of a product and the quantities of products that should be formed from certain quantities of reactants.

Question 22

C2.1.3-How could you use an experiment to identify a metal?

Answer 22

Set up apparatus with gas syringe going into conical flash. Weigh sample of metal and add to flask. Use a measuring cylinder to add 25cm^3 of HCL to flask and quickly replace bung. Measure max volume of gas in syringe. Assume RTP and find moles, then make equation with HCL, X, Cl2 and H2.

Question 23

C2.1.3-What is the limiting reagent?

Answer 23

It is the reactant not in excess which will be used up first and stop the reaction. You can find it out by calculating moles and comparing with equation.

Question 24

C2.1.3-What are the benefits of a high atom economy reaction?

Answer 24

It produces a large proportion of desired products and few unwanted waste products. It it’s important for sustainability as they make the best use of natural resources. They make processes more efficient and preserve raw materials.

Question 25

C2.1.4-What are strong and weak acids?

Answer 25

A strong acid releases all of its hydrogen atoms into solution as H+ ions and completely dissociates in aqueous solution. A weak acid only releases a small amount of its hydrogen atoms into solution as H+ ions and only partially dissociates in aqueous solution.

Question 26

C2.1.4-What are the neutralisation reaction equations?

Answer 26

Acid + Base/alkali-> Salt + Water Acid + Metal Hydroxide -> Salt + Water Acid + Metal Oxide -> Salt + Water Acid + Metal Carbonate -> Salt + Water + Hydrogen

Question 27

C2.1.4-How do you prepare a standard solution for a titration?

Answer 27

The solid is weighed accurately and then dissolved in a beaker using less distilled water than needed to fill volumetric flask to the mark. This solution is transferred to a volumetric flask and last traces are rinsed into flask with distilled water. The flask is carefully filled to the graduation line by adding distilled water a drop at a time until the bottom of the meniscus lines up with the mark. Too much water can dilute solution. Finally, the volumetric flask is inverted several times to mix solution.

Question 28

C2.1.4-How do you carry out an acid-base titration procedure?

Answer 28

Add a measured volume of one solution to a conical flask using a pipette. Add the other solution to a burette and record the initial burette reading to the nearest 0.5cm^3. Add a few drops of indicator to the solution in the conical flask. Run the solution in the burette into the solution in the conical flask, swirling to ensure mixing. Eventually the indicator changes colour at the end point of the titration and the endpoint is used to indicate the volume of one solution that exactly reacts with the volume of the second solution. Record final burette reading and subtract initial from final to get titre(volume of solution added from burette). A quick trial titration is carried out to find approx titre. The titration is then repeated accurately, adding solution drop wise until endpoint is reached. Further titrations are carried out until results are concordant(within 0.1cm^3).

Question 29

C2.1.4-What are uncertainty values?

Answer 29

10cm^3 pipette : +/- 0.04cm^3 25cm^3 pipette : +/- 0.06cm^3 50cm^3 pipette : +/- 0.1cm^3 100cm^3 volumetric flask : +/- 0.2cm^3 250cm^3 volumetric flask : +/- 0.3cm^3

Question 30

C2.1.4-How can you use titration to identity an unknown carbonate?

Answer 30

Prepare a solution of unknown carbonate in a volumetric flask. Using a pipette, measure 25cm^3 of your prepared solution into a conical flask. Using a burette, titrate this solution using 0.1mol dm^-3 hydrochloric acid. Analyse results to identify carbonate(mean titre).

Question 31

C2.1.5-What is an oxidation number?

Answer 31

The number of electrons involved in bonding to a different element. Each atom in a compound has an oxidation number and the sum of the oxidation numbers equate to total charge.

Question 32

C2.1.5-What is oxidation and reduction?

Answer 32

Oxidation is the addition of oxygen and loss of electrons. It is also an increase in oxidation number. Reduction is the removal of oxygen and increase in electrons. It is also a decrease in oxidation number.