2.1 - Atoms and reactions

Question 1

Define isotope

Answer 1

atoms of same element with the same no. protons + electrons but different no. of neutrons, different masses and different physical properties

Question 2

Define relative isotopic mass

Answer 2

mass of an atom of an isotope compared with 1/12th mass of a carbon-12 atom

Question 3

Define relative atomic mass

Answer 3

weighted mean mass of an atom compared with 1/12th mass of a carbon-12 atom

Question 4

Define amount of substance

Answer 4

quantity of a substance present in a sample

Question 5

Give the formulas of the following ions: nitrate, carbonate, sulfate, hydroxide, ammonium, zinc, silver

Answer 5

NO3-
CO3 2-
SO4 2-
OH-
NH4+
Zn2+
Ag+

Question 6

Define mole

Answer 6

unit for amount of substance

Question 7

Define Avogadro constant

Answer 7

no. of particles in a mole

Question 8

Define molar mass

Answer 8

mass per mole of a substance

Question 9

Define molar gas volume

Answer 9

volume of 1 mole of gas

Question 10

Define empirical formula

Answer 10

simplest whole number ratio of atoms of each element present in a compound

Question 11

Define molecular formula

Answer 11

number and type of atoms of each element in a molecule

Question 12

Define water of crystallisation

Answer 12

water molecules that form part of a crystalline structure of a compound

Question 13

State the ideal gas equation and the units for each part

Answer 13

pV=nRT
p in Pa
V in m3
T in K

Question 14

Describe the sustainable benefits of chemical processes with a high atom economy

Answer 14

• reduced costs
• less waste

Question 15

Explain what makes an acid strong or weak

Answer 15

• strong: fully dissociates in solution
• weak: partially dissociates in solution

Question 16

Describe the techniques and procedures when preparing a standard solution

Answer 16

• weigh mass of crystals using a balance with 2 or more decimal places
• dissolve in distilled water and stir with glass rod
• transfer to 250cm3 volumetric flask using funnel
• rinse beaker, glass rod and funnel using distilled water and transfer washings to flask
• make up to mark with more water using a dropping pipette so that bottom of meniscus is on mark
• add stopper and invert several times to mix

Question 17

Describe the techniques and procedures when carrying out an acid-base titration

Answer 17

• use graduated pipette and pipette filler to transfer 25cm3 standard solution to a 250cm3 conical flask
• add two drops of indicator (methyl orange or phenolphthalein)
• fill burette with acid e.g HCl and record initial reading
• open tap and add to conical flask until end point is reached (colour change), drop wise at end
• record final burette reading and calculate titre
• repeat until concordant results obtained and calculate mean using only concordant titres

Question 18

Define alkali

Answer 18

releases OH- ions in aqueous solution

Question 19

Define acid

Answer 19

releases H+ ions in aqueous solution

Question 20

Define standard solution

Answer 20

solution of known concentration

Question 21

Define base

Answer 21

substance which readily accepts H+ ions

Question 22

What are concordant results?

Answer 22

titres within 0.1cm3 of each other

Question 23

Give the colour changes for methyl orange and phenolphthalein

Answer 23

Methyl orange: yellow (alkali), orange (acid)
Phenolphthalein: pink (alkali), colourless (acid)

Question 24

Define oxidation

Answer 24

loss of electrons

Question 25

Define reduction

Answer 25

gain of electrons

Question 26

Define disproportionation

Answer 26

redox reaction when same element is oxidised and reduced

Question 27

Why may theoretical yield not be obtained?

Answer 27

• reaction not completed
• side reactions may take place
• purification may lead to loss of product

Question 28

Suggest two modifications to a method that can reduce % uncertainty

Answer 28

• use a larger mass
• use balance which weighs to more decimal places

Question 29

How to obtain a sample of ionic compound after reaction with acid?

Answer 29

• filter using funnel and filter paper to obtain solid
• dry