Chapter 2 & 3 Atoms, Ions, Moles Flashcards by Heer Arora

What are isotopes

Atoms of the same element with different numbers of neutrons and different masses

How well did you know this?

Not at all

Perfectly

what is relative isotopic mass

the mass of an atom of an isotope compared to 1/12 of the mass of a 12C atom.

How well did you know this?

Not at all

Perfectly

what is relative atomic mass

the weighted mean mass of 1 mole of an element compared to the mass of 1 mole of 12C

How well did you know this?

Not at all

Perfectly

atomic number =

amount of protons

How well did you know this?

Not at all

Perfectly

A represents the […] number

Mass

How well did you know this?

Not at all

Perfectly

Z represents the […]

Proton number

How well did you know this?

Not at all

Perfectly

How come isotopes still react in the same way

The number of neutrons has no effect on the reactions of an element

How well did you know this?

Not at all

Perfectly

Cations are

Positive ions (atoms w fewer electrons than protons)

How well did you know this?

Not at all

Perfectly

Anions are

Negative ions (atoms with more electrons than protons)

How well did you know this?

Not at all

Perfectly

Ions and atoms of an element have the same number of […] but a different number of […]

Protons, electons

How well did you know this?

Not at all

Perfectly

mass to charge ratio =

relative mass of ion / relative charge on ion

How well did you know this?

Not at all

Perfectly

In a mass spectrometer, heavier ions move […] than lighter ones and are more difficult to […]

Slower, deflect

How well did you know this?

Not at all

Perfectly

What happens after a sample is placed in the mass spectrometer

The sample is vaporised and then ionised to form postive ions
-> then the ions are accelerated and move

How well did you know this?

Not at all

Perfectly

relative isotopic mass =

( the abundance x the mass number ) / 100

How well did you know this?

Not at all

Perfectly

Relative molecular mass is used for

Simple molecules

How well did you know this?

Not at all

Perfectly

For compounds with giant structures, we use

Relative formula mass

How well did you know this?

Not at all

Perfectly

What is a binary compound

Compound that only contains 2 elements

When constructing a balanced equation what do you do

first get the ions and charges right and come up with the formulae

e.g Aluminium oxide will be Al2O3 due to Al being 3+ and O being 2-

then get the atoms equal on boths sides so its

4Al (s) + 3O2 (g) -> 2Al2O3

What is amount of substance

The number of particles in a substance, measured in moles (mol)

What is the avogadro constant

6.02 x 10^23 mol^-1

-> the number of particles in each mole of carbon 12

What is the molar mass

Mass per mole of a substance

Amount of substance (n) =

Mass (m) / molar mass (M)

what is the molar gas volume (the volume occupied by any 1 mole of any has at rt and rtp)

24 dm^3 mol^-1

What is empirical formula

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

What is molecular formula

The number and type of atoms of each element in a molecule

Empirical formula from mass worked example

1.203g of calcium combines with 2.13g of chlorine to form a compound n(Ca) = 1.203/40.1 = 0.03 mol n(Cl) = 2.13/35.5 = 0.06 mol n(Ca):n(Cl) = 0.03/0.03 : 0.06/0.03 = 1:2 therefore it’s CaCl2

Molecular formula worked example

Chemical analysis of a compound gave the percentage composition by mass C: 40.00%; H: 6.67%: O: 53.33% [Ar: C, 12.0; H, 1.0; 0, 16.0] The relative molecular mass of the compound is 180.0. Step 1: Convert % by mass into moles of atoms using n=m/M: C = 40.00/12 = 3.33 mol H = 6.67 / 1 = 6.67 mol O = 53.33 / 16 = 3.33 mol Step 2: Find smallest whole-number ratio and empirical formula. 3.33/3.33 = 1 and 6.67/3.33 = 2 Ratio of C:H:O= 1:2:1 = CH2O -> Write the relative mass of the empirical formula CH2O: 12.0 + 1.0 x 2 + 16.0 = 30.0 -> Find number of CH2O units in one molecule: 180 / 30= 6 ->Write the molecular formula: CH2O x 6 = C6H12O6

Atom economy =

Sum of desired products / sum of all products

Benefits of high atom economy

- more efficient - reduces waste - preserves raw materials

Percentage yield =

(Actual yield / theoretical yield) x 100

why is it hard to achieve theoretical yield

- reaction may not go to completion - side reactions may have taken place - purification of produce may result in some loss of it

What is the limiting reagent

The reactant that is used up first

2H2 (g) + O2 (g) -> 2H2O (l) Why is hydrogen the limiting reagent

2 mol of H are needed for every mol of O -> if an equal amount of both were used, the H would get all used up ans only half of the O

1cm ^3 = ? Ml

1 ml

1 dm ^ 3 = ? cm ^3 and ? ml

1000 for both

amount [n] (mol) =

concentration [c] (mol dm^-3) x volume [V] dm^3

Worked example converting between solution volumes and moles (mol from solution)

Calculate the amount of NaCI, in mol, in 30.0 cm^3 of a 2.00 mol dm-3 solution. n (NaCl) = c x V (cm^3) / 1000 = 2.00 x 30/1000 = 0.06 mol

Worked example converting between solution volumes and moles (solution volume from mol)

Calculate the volume of a 0.160 mol dm-3 solution that contains 3.25 x 10^-3 mol of NaCI. n = c x V(cm^3) / 1000 so V = 1000 x n / c = 1000 x 3.25 x 10^-3 / 0.16 = 20.3 cm^3

What’s a standard solution

A solution of known concentration

How are standard solutions prepared

By dissolving an exact mass of the solute in a solvent and then making the solution an exact volume

Worked Example: Calculate the mass of Na2CO3 required to prepare 100cm^3 of a 0.250 mol dm^3 standard solution

1. Work out the amout in moles required n (Na2CO3) = c x [V (in cm^3)/1000] = 0.250 x 100/1000 = 0.0250 mol 2. Work out the molar mass of Na2CO3 -> its 106 g 3. Work out the mass using n = m/M m = n x M = 0.0250 x 106 = 2.65g