IAS Edx Chemistry - Unit 1 - Topic 1: Formula, Equations & Amounts

Vocabulary practice flashcards covering chemical formulae, equation types, stoichiometry, mole calculations, gas laws, and empirical/molecular formula determinations.

Valency Method for Writing Formulae

A three-step method to write a chemical formula: 1. Write down the symbols of elements forming the compound. 2. Write the valency of each element below its symbol. 3. Cross the valencies.

Polyatomic Ion

An ion composed of two or more covalently bonded atoms carrying an overall charge (for example, ammonium $NH_4^+$, hydroxide $OH^-$, nitrate $NO_3^-$, hydrogencarbonate $HCO_3^-$, carbonate $CO_3^{2-}$, sulfate $SO_4^{2-}$, and phosphate $PO_4^{3-}$).

Spectator Ions

Ions that are present on both the reactant and product sides of a chemical equation without taking part in the reaction, which are omitted when writing a net ionic equation.

Net Ionic Equation

A chemical equation that includes only those species directly participating in the chemical reaction, written by replacing aqueous ionic compounds with separate aqueous ions and deleting identical spectator ions from both sides.

Metal ion—> positive

Non metal ion—→ negative

Displacement Reaction

A chemical reaction in which a more reactive element displaces a less reactive element from its compound.

Thermite Method

A highly exothermic solid-state displacement reaction between aluminium and iron(III) oxide ($2 Al_{(s)} + Fe_2O_{3(s)} \rightarrow Al_2O_{3(s)} + 2 Fe_{(s)}$) initiated by a burning magnesium fuse, producing molten iron used to weld metals.

Precipitation Reaction

A chemical reaction where two solutions containing soluble substances are mixed together to form an insoluble solid known as a precipitate.

Neutralization Reaction

A reaction between an acid and a base (or alkali, metal carbonate, or hydrogen carbonate) forming water and a salt; it is not a redox reaction because no oxidation numbers change.

Relative Atomic Mass ($A_r$)

The weighted average mass of atoms of an element compared to $1/12$ of the mass of an atom of Carbon-12.

Relative Molecular Mass ($M_r$)

The sum of the relative atomic masses ($A_r$) of all the atoms present in the formula of a covalent molecule.

Relative Formula Mass

The sum of the relative atomic masses ($A_r$) of all atoms shown in the chemical formula, applied specifically to ionic compounds.

Molar Mass ($M$)

The mass of one mole of a substance expressed in grams per mole

Mole ($n$)

The SI unit for the amount of substance; defined as the amount of substance that contains the same number of particles as the number of carbon atoms in $12\,g$ of Carbon-12.

Avogadro's Constant ($L$)

The number of particles (atoms, ions, or molecules) present in one mole of any substance, equal to $6.02 \times 10^{23}$.

Mass-Mole Relationship

The stoichiometric formula relating mass ($m$ in $g$), molar mass ($M$ in $g\,mol^{-1}$), and amount of substance ($n$ in $mol$), given by

$n = \frac{m}{M}$.

Theoretical Yield

The maximum possible mass of a product that can be formed in a chemical reaction, calculated from the balanced equation assuming complete reaction of the limiting reactant.

Actual Yield

The actual mass of product obtained experimentally by weighing the product collected after carrying out the reaction.

Percentage Yield

A measure of the practical efficiency of a reaction, given by

$\frac{\text{Actual yield}}{\text{Theoretical yield}} \times 100$ .

Reasons why the actual mass is lower than theoretical mass

-incomplete reaction →where not all the Reactions reacted

-loss of products during transfer →where some products are left in the apparatus

-Side reactions occurred →where some reactants form unwanted products instead

-Loss During filtration →Where some product passes through

-reversible reaction →where the reaction does not go completely to the right

-Impure reactants

Atom Economy

The percentage of atoms from the starting materials that end up in the desired product, calculated as

$\frac{\text{molar mass of desired product}}{\text{sum of molar masses of all products}} \times 100$.

Mass of element in a compound

Molar Gas Volume ($V_m$)

The volume occupied by one mole of any gas at room temperature and pressure (r.t.p.), equal to $24\,dm^3\,mol^{-1}$ (or $24\,000\,cm^3\,mol^{-1}$).

Ideal Gas Equation

The state equation $pV = nRT$ applied to gases and volatile liquids above their boiling temperatures, where pressure $p$ is in $Pa$, volume $V$ is in $m^3$, temperature $T$ is in $K$, and $R = 8.31\,J\,mol^{-1}\,K^{-1}$.

Molar Concentration

The amount of a solute in moles dissolved per unit volume of solution, calculated as

$c = \frac{n}{V}$ and expressed in $mol\,dm^{-3}$.

Mass Concentration

The mass of solute in grams dissolved per unit volume of solution in cubic decimetres, calculated as

$\text{mass concentration} = \frac{m}{V}$ and expressed in $g\,dm^{-3}$.

Concentration in Parts Per Million (ppm)

A unit of concentration representing the number of parts of one substance per million parts of another, given by

$\frac{\text{mass of solute}}{\text{mass of solvent}} \times 10^6$ for solutions or $\frac{\text{volume of gas}}{\text{volume of air}} \times 10^6$ for gases.

Empirical Formula

The chemical formula showing the simplest whole-number ratio of atoms of each element present in a compound.

Molecular Formula

The chemical formula showing the actual number of atoms of each element present in a single molecule of a compound, calculated as

$\text{Empirical Formula} \times \frac{M_r\text{ of compound}}{M_r\text{ of empirical formula}}$.

Working out equations from reacting masses

1) write down molar mass of each substance

2) calculate no. Of moles of each substance

3) divide by the smallest no. To get a whole digit ratio

Combustion Analysis of Magnesium Oxide

A laboratory procedure in which magnesium ribbon is burned inside a crucible with the lid occasionally lifted to admit oxygen, allowing determination of the oxide's empirical formula from the mass gain.

Reduction Analysis of Copper Oxide

A laboratory procedure in which dry hydrogen gas is passed over heated copper oxide in a reduction tube, removing oxygen to form water and copper solid, allowing calculation of the empirical formula from mass loss.

What is the formula and charge for-

Ammonium

NH4 charge +1

Formula and charge for

Hydroxide

OH Charge -1

Formula and charge of

Hydrogen carbonate

HCO3 charge -1

Formula and charge of

Carbonate

CO3 charge -2

Formula and charge of

Sulfate

SO4 charge -2

Formula and charge of

Nitrate

NO3 charge -1

Formula and charge of phosphate

PO4 charge -3

Calculating the limiting/ excess reactant

1-find the no of moles

2-divide the moles by its coefficient in the balanced equation

3-the smaller value= limiting reactant

Acid+metal —→

Salt +hydrogen

Acid + metal oxide/hydroxide ———>

Salt+water

Acid+ metal carbonate ——>

Salt +water +carbon dioxide

Acid + alkali——>

Salt +water

Acid +hydrogen carbonate——>

Salt +water +carbon dioxide

Acid + ammonia —→

Ammonium salt

Metal + oxygen—→

Metal oxide

Metal + water—- >

Metal hydroxide +hydrogen

Metal + steam——>

Metal oxide +hydrogen

More reactive metal+salt solution——>

New salt +less reactive metal

Metal oxide +water ——>

Metal hydroxide

Non Metal oxide + acid —→

Salt +water

Non metal oxide +water ——>

Acid

Hydrocarbon +excess oxygen——→

Carbon dioxide +water

Hydrocarbon +limited oxygen——>

Carbon monoxide +water

Acid

Usually starts with a H

Alkali

Usually contains a metal bonded to OH and dissolves in water

Bases that aren’t Alkalis

Metal oxides or hydroxides that are insoluble in water

All nitrates

Soluble

All sulfates are

Soluble except calcium barium and lead

All halides are

Soluble except silver and lead

All carbonates

Are insoluble except group 1 and ammonium

All oxides and hydroxides are

Insoluble except group 1, calcium and ammonium